node/deps/libev/ev.pod


								=head1 NAME


								libev - a high performance full-featured event loop written in C


								=head1 SYNOPSIS


								   #include <ev.h>


								=head2 EXAMPLE PROGRAM


								   // a single header file is required

								   #include <ev.h>


								   #include <stdio.h> // for puts


								   // every watcher type has its own typedef'd struct

								   // with the name ev_TYPE

								   ev_io stdin_watcher;

								   ev_timer timeout_watcher;


								   // all watcher callbacks have a similar signature

								   // this callback is called when data is readable on stdin

								   static void

								   stdin_cb (EV_P_ ev_io *w, int revents)

								   {

								     puts ("stdin ready");

								     // for one-shot events, one must manually stop the watcher

								     // with its corresponding stop function.

								     ev_io_stop (EV_A_ w);


								     // this causes all nested ev_run's to stop iterating

								     ev_break (EV_A_ EVBREAK_ALL);

								   }


								   // another callback, this time for a time-out

								   static void

								   timeout_cb (EV_P_ ev_timer *w, int revents)

								   {

								     puts ("timeout");

								     // this causes the innermost ev_run to stop iterating

								     ev_break (EV_A_ EVBREAK_ONE);

								   }


								   int

								   main (void)

								   {

								     // use the default event loop unless you have special needs

								     struct ev_loop *loop = EV_DEFAULT;


								     // initialise an io watcher, then start it

								     // this one will watch for stdin to become readable

								     ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);

								     ev_io_start (loop, &stdin_watcher);


								     // initialise a timer watcher, then start it

								     // simple non-repeating 5.5 second timeout

								     ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);

								     ev_timer_start (loop, &timeout_watcher);


								     // now wait for events to arrive

								     ev_run (loop, 0);


								     // break was called, so exit

								     return 0;

								   }


								=head1 ABOUT THIS DOCUMENT


								This document documents the libev software package.


								The newest version of this document is also available as an html-formatted

								web page you might find easier to navigate when reading it for the first

								time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.


								While this document tries to be as complete as possible in documenting

								libev, its usage and the rationale behind its design, it is not a tutorial

								on event-based programming, nor will it introduce event-based programming

								with libev.


								Familiarity with event based programming techniques in general is assumed

								throughout this document.


								=head1 WHAT TO READ WHEN IN A HURRY


								This manual tries to be very detailed, but unfortunately, this also makes

								it very long. If you just want to know the basics of libev, I suggest

								reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and

								look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and

								C<ev_timer> sections in L<WATCHER TYPES>.


								=head1 ABOUT LIBEV


								Libev is an event loop: you register interest in certain events (such as a

								file descriptor being readable or a timeout occurring), and it will manage

								these event sources and provide your program with events.


								To do this, it must take more or less complete control over your process

								(or thread) by executing the I<event loop> handler, and will then

								communicate events via a callback mechanism.


								You register interest in certain events by registering so-called I<event

								watchers>, which are relatively small C structures you initialise with the

								details of the event, and then hand it over to libev by I<starting> the

								watcher.


								=head2 FEATURES


								Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the

								BSD-specific C<kqueue> and the Solaris-specific event port mechanisms

								for file descriptor events (C<ev_io>), the Linux C<inotify> interface

								(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner

								inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative

								timers (C<ev_timer>), absolute timers with customised rescheduling

								(C<ev_periodic>), synchronous signals (C<ev_signal>), process status

								change events (C<ev_child>), and event watchers dealing with the event

								loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and

								C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even

								limited support for fork events (C<ev_fork>).


								It also is quite fast (see this

								L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent

								for example).


								=head2 CONVENTIONS


								Libev is very configurable. In this manual the default (and most common)

								configuration will be described, which supports multiple event loops. For

								more info about various configuration options please have a look at

								B<EMBED> section in this manual. If libev was configured without support

								for multiple event loops, then all functions taking an initial argument of

								name C<loop> (which is always of type C<struct ev_loop *>) will not have

								this argument.


								=head2 TIME REPRESENTATION


								Libev represents time as a single floating point number, representing

								the (fractional) number of seconds since the (POSIX) epoch (in practice

								somewhere near the beginning of 1970, details are complicated, don't

								ask). This type is called C<ev_tstamp>, which is what you should use

								too. It usually aliases to the C<double> type in C. When you need to do

								any calculations on it, you should treat it as some floating point value.


								Unlike the name component C<stamp> might indicate, it is also used for

								time differences (e.g. delays) throughout libev.


								=head1 ERROR HANDLING


								Libev knows three classes of errors: operating system errors, usage errors

								and internal errors (bugs).


								When libev catches an operating system error it cannot handle (for example

								a system call indicating a condition libev cannot fix), it calls the callback

								set via C<ev_set_syserr_cb>, which is supposed to fix the problem or

								abort. The default is to print a diagnostic message and to call C<abort

								()>.


								When libev detects a usage error such as a negative timer interval, then

								it will print a diagnostic message and abort (via the C<assert> mechanism,

								so C<NDEBUG> will disable this checking): these are programming errors in

								the libev caller and need to be fixed there.


								Libev also has a few internal error-checking C<assert>ions, and also has

								extensive consistency checking code. These do not trigger under normal

								circumstances, as they indicate either a bug in libev or worse.


								=head1 GLOBAL FUNCTIONS


								These functions can be called anytime, even before initialising the

								library in any way.


								=over 4


								=item ev_tstamp ev_time ()


								Returns the current time as libev would use it. Please note that the

								C<ev_now> function is usually faster and also often returns the timestamp

								you actually want to know. Also interesting is the combination of

								C<ev_update_now> and C<ev_now>.


								=item ev_sleep (ev_tstamp interval)


								Sleep for the given interval: The current thread will be blocked until

								either it is interrupted or the given time interval has passed. Basically

								this is a sub-second-resolution C<sleep ()>.


								=item int ev_version_major ()


								=item int ev_version_minor ()


								You can find out the major and minor ABI version numbers of the library

								you linked against by calling the functions C<ev_version_major> and

								C<ev_version_minor>. If you want, you can compare against the global

								symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the

								version of the library your program was compiled against.


								These version numbers refer to the ABI version of the library, not the

								release version.


								Usually, it's a good idea to terminate if the major versions mismatch,

								as this indicates an incompatible change. Minor versions are usually

								compatible to older versions, so a larger minor version alone is usually

								not a problem.


								Example: Make sure we haven't accidentally been linked against the wrong

								version (note, however, that this will not detect other ABI mismatches,

								such as LFS or reentrancy).


								   assert (("libev version mismatch",

								            ev_version_major () == EV_VERSION_MAJOR

								            && ev_version_minor () >= EV_VERSION_MINOR));


								=item unsigned int ev_supported_backends ()


								Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>

								value) compiled into this binary of libev (independent of their

								availability on the system you are running on). See C<ev_default_loop> for

								a description of the set values.


								Example: make sure we have the epoll method, because yeah this is cool and

								a must have and can we have a torrent of it please!!!11


								   assert (("sorry, no epoll, no sex",

								            ev_supported_backends () & EVBACKEND_EPOLL));


								=item unsigned int ev_recommended_backends ()


								Return the set of all backends compiled into this binary of libev and

								also recommended for this platform, meaning it will work for most file

								descriptor types. This set is often smaller than the one returned by

								C<ev_supported_backends>, as for example kqueue is broken on most BSDs

								and will not be auto-detected unless you explicitly request it (assuming

								you know what you are doing). This is the set of backends that libev will

								probe for if you specify no backends explicitly.


								=item unsigned int ev_embeddable_backends ()


								Returns the set of backends that are embeddable in other event loops. This

								value is platform-specific but can include backends not available on the

								current system. To find which embeddable backends might be supported on

								the current system, you would need to look at C<ev_embeddable_backends ()

								& ev_supported_backends ()>, likewise for recommended ones.


								See the description of C<ev_embed> watchers for more info.


								=item ev_set_allocator (void *(*cb)(void *ptr, long size))


								Sets the allocation function to use (the prototype is similar - the

								semantics are identical to the C<realloc> C89/SuS/POSIX function). It is

								used to allocate and free memory (no surprises here). If it returns zero

								when memory needs to be allocated (C<size != 0>), the library might abort

								or take some potentially destructive action.


								Since some systems (at least OpenBSD and Darwin) fail to implement

								correct C<realloc> semantics, libev will use a wrapper around the system

								C<realloc> and C<free> functions by default.


								You could override this function in high-availability programs to, say,

								free some memory if it cannot allocate memory, to use a special allocator,

								or even to sleep a while and retry until some memory is available.


								Example: Replace the libev allocator with one that waits a bit and then

								retries (example requires a standards-compliant C<realloc>).


								   static void *

								   persistent_realloc (void *ptr, size_t size)

								   {

								     for (;;)

								       {

								         void *newptr = realloc (ptr, size);


								         if (newptr)

								           return newptr;


								         sleep (60);

								       }

								   }


								   ...

								   ev_set_allocator (persistent_realloc);


								=item ev_set_syserr_cb (void (*cb)(const char *msg))


								Set the callback function to call on a retryable system call error (such

								as failed select, poll, epoll_wait). The message is a printable string

								indicating the system call or subsystem causing the problem. If this

								callback is set, then libev will expect it to remedy the situation, no

								matter what, when it returns. That is, libev will generally retry the

								requested operation, or, if the condition doesn't go away, do bad stuff

								(such as abort).


								Example: This is basically the same thing that libev does internally, too.


								   static void

								   fatal_error (const char *msg)

								   {

								     perror (msg);

								     abort ();

								   }


								   ...

								   ev_set_syserr_cb (fatal_error);


								=item ev_feed_signal (int signum)


								This function can be used to "simulate" a signal receive. It is completely

								safe to call this function at any time, from any context, including signal

								handlers or random threads.


								Its main use is to customise signal handling in your process, especially

								in the presence of threads. For example, you could block signals

								by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when

								creating any loops), and in one thread, use C<sigwait> or any other

								mechanism to wait for signals, then "deliver" them to libev by calling

								C<ev_feed_signal>.


								=back


								=head1 FUNCTIONS CONTROLLING EVENT LOOPS


								An event loop is described by a C<struct ev_loop *> (the C<struct> is

								I<not> optional in this case unless libev 3 compatibility is disabled, as

								libev 3 had an C<ev_loop> function colliding with the struct name).


								The library knows two types of such loops, the I<default> loop, which

								supports child process events, and dynamically created event loops which

								do not.


								=over 4


								=item struct ev_loop *ev_default_loop (unsigned int flags)


								This returns the "default" event loop object, which is what you should

								normally use when you just need "the event loop". Event loop objects and

								the C<flags> parameter are described in more detail in the entry for

								C<ev_loop_new>.


								If the default loop is already initialised then this function simply

								returns it (and ignores the flags. If that is troubling you, check

								C<ev_backend ()> afterwards). Otherwise it will create it with the given

								flags, which should almost always be C<0>, unless the caller is also the

								one calling C<ev_run> or otherwise qualifies as "the main program".


								If you don't know what event loop to use, use the one returned from this

								function (or via the C<EV_DEFAULT> macro).


								Note that this function is I<not> thread-safe, so if you want to use it

								from multiple threads, you have to employ some kind of mutex (note also

								that this case is unlikely, as loops cannot be shared easily between

								threads anyway).


								The default loop is the only loop that can handle C<ev_child> watchers,

								and to do this, it always registers a handler for C<SIGCHLD>. If this is

								a problem for your application you can either create a dynamic loop with

								C<ev_loop_new> which doesn't do that, or you can simply overwrite the

								C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.


								Example: This is the most typical usage.


								   if (!ev_default_loop (0))

								     fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");


								Example: Restrict libev to the select and poll backends, and do not allow

								environment settings to be taken into account:


								   ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);


								=item struct ev_loop *ev_loop_new (unsigned int flags)


								This will create and initialise a new event loop object. If the loop

								could not be initialised, returns false.


								This function is thread-safe, and one common way to use libev with

								threads is indeed to create one loop per thread, and using the default

								loop in the "main" or "initial" thread.


								The flags argument can be used to specify special behaviour or specific

								backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).


								The following flags are supported:


								=over 4


								=item C<EVFLAG_AUTO>


								The default flags value. Use this if you have no clue (it's the right

								thing, believe me).


								=item C<EVFLAG_NOENV>


								If this flag bit is or'ed into the flag value (or the program runs setuid

								or setgid) then libev will I<not> look at the environment variable

								C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will

								override the flags completely if it is found in the environment. This is

								useful to try out specific backends to test their performance, or to work

								around bugs.


								=item C<EVFLAG_FORKCHECK>


								Instead of calling C<ev_loop_fork> manually after a fork, you can also

								make libev check for a fork in each iteration by enabling this flag.


								This works by calling C<getpid ()> on every iteration of the loop,

								and thus this might slow down your event loop if you do a lot of loop

								iterations and little real work, but is usually not noticeable (on my

								GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence

								without a system call and thus I<very> fast, but my GNU/Linux system also has

								C<pthread_atfork> which is even faster).


								The big advantage of this flag is that you can forget about fork (and

								forget about forgetting to tell libev about forking) when you use this

								flag.


								This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>

								environment variable.


								=item C<EVFLAG_NOINOTIFY>


								When this flag is specified, then libev will not attempt to use the

								I<inotify> API for its C<ev_stat> watchers. Apart from debugging and

								testing, this flag can be useful to conserve inotify file descriptors, as

								otherwise each loop using C<ev_stat> watchers consumes one inotify handle.


								=item C<EVFLAG_SIGNALFD>


								When this flag is specified, then libev will attempt to use the

								I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API

								delivers signals synchronously, which makes it both faster and might make

								it possible to get the queued signal data. It can also simplify signal

								handling with threads, as long as you properly block signals in your

								threads that are not interested in handling them.


								Signalfd will not be used by default as this changes your signal mask, and

								there are a lot of shoddy libraries and programs (glib's threadpool for

								example) that can't properly initialise their signal masks.


								=item C<EVFLAG_NOSIGMASK>


								When this flag is specified, then libev will avoid to modify the signal

								mask. Specifically, this means you ahve to make sure signals are unblocked

								when you want to receive them.


								This behaviour is useful when you want to do your own signal handling, or

								want to handle signals only in specific threads and want to avoid libev

								unblocking the signals.


								It's also required by POSIX in a threaded program, as libev calls

								C<sigprocmask>, whose behaviour is officially unspecified.


								This flag's behaviour will become the default in future versions of libev.


								=item C<EVBACKEND_SELECT>  (value 1, portable select backend)


								This is your standard select(2) backend. Not I<completely> standard, as

								libev tries to roll its own fd_set with no limits on the number of fds,

								but if that fails, expect a fairly low limit on the number of fds when

								using this backend. It doesn't scale too well (O(highest_fd)), but its

								usually the fastest backend for a low number of (low-numbered :) fds.


								To get good performance out of this backend you need a high amount of

								parallelism (most of the file descriptors should be busy). If you are

								writing a server, you should C<accept ()> in a loop to accept as many

								connections as possible during one iteration. You might also want to have

								a look at C<ev_set_io_collect_interval ()> to increase the amount of

								readiness notifications you get per iteration.


								This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the

								C<writefds> set (and to work around Microsoft Windows bugs, also onto the

								C<exceptfds> set on that platform).


								=item C<EVBACKEND_POLL>    (value 2, poll backend, available everywhere except on windows)


								And this is your standard poll(2) backend. It's more complicated

								than select, but handles sparse fds better and has no artificial

								limit on the number of fds you can use (except it will slow down

								considerably with a lot of inactive fds). It scales similarly to select,

								i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for

								performance tips.


								This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and

								C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.


								=item C<EVBACKEND_EPOLL>   (value 4, Linux)


								Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9

								kernels).


								For few fds, this backend is a bit little slower than poll and select,

								but it scales phenomenally better. While poll and select usually scale

								like O(total_fds) where n is the total number of fds (or the highest fd),

								epoll scales either O(1) or O(active_fds).


								The epoll mechanism deserves honorable mention as the most misdesigned

								of the more advanced event mechanisms: mere annoyances include silently

								dropping file descriptors, requiring a system call per change per file

								descriptor (and unnecessary guessing of parameters), problems with dup,

								returning before the timeout value, resulting in additional iterations

								(and only giving 5ms accuracy while select on the same platform gives

								0.1ms) and so on. The biggest issue is fork races, however - if a program

								forks then I<both> parent and child process have to recreate the epoll

								set, which can take considerable time (one syscall per file descriptor)

								and is of course hard to detect.


								Epoll is also notoriously buggy - embedding epoll fds I<should> work, but

								of course I<doesn't>, and epoll just loves to report events for totally

								I<different> file descriptors (even already closed ones, so one cannot

								even remove them from the set) than registered in the set (especially

								on SMP systems). Libev tries to counter these spurious notifications by

								employing an additional generation counter and comparing that against the

								events to filter out spurious ones, recreating the set when required. Last

								not least, it also refuses to work with some file descriptors which work

								perfectly fine with C<select> (files, many character devices...).


								Epoll is truly the train wreck analog among event poll mechanisms,

								a frankenpoll, cobbled together in a hurry, no thought to design or

								interaction with others.


								While stopping, setting and starting an I/O watcher in the same iteration

								will result in some caching, there is still a system call per such

								incident (because the same I<file descriptor> could point to a different

								I<file description> now), so its best to avoid that. Also, C<dup ()>'ed

								file descriptors might not work very well if you register events for both

								file descriptors.


								Best performance from this backend is achieved by not unregistering all

								watchers for a file descriptor until it has been closed, if possible,

								i.e. keep at least one watcher active per fd at all times. Stopping and

								starting a watcher (without re-setting it) also usually doesn't cause

								extra overhead. A fork can both result in spurious notifications as well

								as in libev having to destroy and recreate the epoll object, which can

								take considerable time and thus should be avoided.


								All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or

								faster than epoll for maybe up to a hundred file descriptors, depending on

								the usage. So sad.


								While nominally embeddable in other event loops, this feature is broken in

								all kernel versions tested so far.


								This backend maps C<EV_READ> and C<EV_WRITE> in the same way as

								C<EVBACKEND_POLL>.


								=item C<EVBACKEND_KQUEUE>  (value 8, most BSD clones)


								Kqueue deserves special mention, as at the time of this writing, it

								was broken on all BSDs except NetBSD (usually it doesn't work reliably

								with anything but sockets and pipes, except on Darwin, where of course

								it's completely useless). Unlike epoll, however, whose brokenness

								is by design, these kqueue bugs can (and eventually will) be fixed

								without API changes to existing programs. For this reason it's not being

								"auto-detected" unless you explicitly specify it in the flags (i.e. using

								C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)

								system like NetBSD.


								You still can embed kqueue into a normal poll or select backend and use it

								only for sockets (after having made sure that sockets work with kqueue on

								the target platform). See C<ev_embed> watchers for more info.


								It scales in the same way as the epoll backend, but the interface to the

								kernel is more efficient (which says nothing about its actual speed, of

								course). While stopping, setting and starting an I/O watcher does never

								cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to

								two event changes per incident. Support for C<fork ()> is very bad (but

								sane, unlike epoll) and it drops fds silently in similarly hard-to-detect

								cases


								This backend usually performs well under most conditions.


								While nominally embeddable in other event loops, this doesn't work

								everywhere, so you might need to test for this. And since it is broken

								almost everywhere, you should only use it when you have a lot of sockets

								(for which it usually works), by embedding it into another event loop

								(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course

								also broken on OS X)) and, did I mention it, using it only for sockets.


								This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with

								C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with

								C<NOTE_EOF>.


								=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)


								This is not implemented yet (and might never be, unless you send me an

								implementation). According to reports, C</dev/poll> only supports sockets

								and is not embeddable, which would limit the usefulness of this backend

								immensely.


								=item C<EVBACKEND_PORT>    (value 32, Solaris 10)


								This uses the Solaris 10 event port mechanism. As with everything on Solaris,

								it's really slow, but it still scales very well (O(active_fds)).


								While this backend scales well, it requires one system call per active

								file descriptor per loop iteration. For small and medium numbers of file

								descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend

								might perform better.


								On the positive side, this backend actually performed fully to

								specification in all tests and is fully embeddable, which is a rare feat

								among the OS-specific backends (I vastly prefer correctness over speed

								hacks).


								On the negative side, the interface is I<bizarre> - so bizarre that

								even sun itself gets it wrong in their code examples: The event polling

								function sometimes returning events to the caller even though an error

								occurred, but with no indication whether it has done so or not (yes, it's

								even documented that way) - deadly for edge-triggered interfaces where

								you absolutely have to know whether an event occurred or not because you

								have to re-arm the watcher.


								Fortunately libev seems to be able to work around these idiocies.


								This backend maps C<EV_READ> and C<EV_WRITE> in the same way as

								C<EVBACKEND_POLL>.


								=item C<EVBACKEND_ALL>


								Try all backends (even potentially broken ones that wouldn't be tried

								with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as

								C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.


								It is definitely not recommended to use this flag, use whatever

								C<ev_recommended_backends ()> returns, or simply do not specify a backend

								at all.


								=item C<EVBACKEND_MASK>


								Not a backend at all, but a mask to select all backend bits from a

								C<flags> value, in case you want to mask out any backends from a flags

								value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).


								=back


								If one or more of the backend flags are or'ed into the flags value,

								then only these backends will be tried (in the reverse order as listed

								here). If none are specified, all backends in C<ev_recommended_backends

								()> will be tried.


								Example: Try to create a event loop that uses epoll and nothing else.


								   struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);

								   if (!epoller)

								     fatal ("no epoll found here, maybe it hides under your chair");


								Example: Use whatever libev has to offer, but make sure that kqueue is

								used if available.


								   struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);


								=item ev_loop_destroy (loop)


								Destroys an event loop object (frees all memory and kernel state

								etc.). None of the active event watchers will be stopped in the normal

								sense, so e.g. C<ev_is_active> might still return true. It is your

								responsibility to either stop all watchers cleanly yourself I<before>

								calling this function, or cope with the fact afterwards (which is usually

								the easiest thing, you can just ignore the watchers and/or C<free ()> them

								for example).


								Note that certain global state, such as signal state (and installed signal

								handlers), will not be freed by this function, and related watchers (such

								as signal and child watchers) would need to be stopped manually.


								This function is normally used on loop objects allocated by

								C<ev_loop_new>, but it can also be used on the default loop returned by

								C<ev_default_loop>, in which case it is not thread-safe.


								Note that it is not advisable to call this function on the default loop

								except in the rare occasion where you really need to free its resources.

								If you need dynamically allocated loops it is better to use C<ev_loop_new>

								and C<ev_loop_destroy>.


								=item ev_loop_fork (loop)


								This function sets a flag that causes subsequent C<ev_run> iterations to

								reinitialise the kernel state for backends that have one. Despite the

								name, you can call it anytime, but it makes most sense after forking, in

								the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the

								child before resuming or calling C<ev_run>.


								Again, you I<have> to call it on I<any> loop that you want to re-use after

								a fork, I<even if you do not plan to use the loop in the parent>. This is

								because some kernel interfaces *cough* I<kqueue> *cough* do funny things

								during fork.


								On the other hand, you only need to call this function in the child

								process if and only if you want to use the event loop in the child. If

								you just fork+exec or create a new loop in the child, you don't have to

								call it at all (in fact, C<epoll> is so badly broken that it makes a

								difference, but libev will usually detect this case on its own and do a

								costly reset of the backend).


								The function itself is quite fast and it's usually not a problem to call

								it just in case after a fork.


								Example: Automate calling C<ev_loop_fork> on the default loop when

								using pthreads.


								   static void

								   post_fork_child (void)

								   {

								     ev_loop_fork (EV_DEFAULT);

								   }


								   ...

								   pthread_atfork (0, 0, post_fork_child);


								=item int ev_is_default_loop (loop)


								Returns true when the given loop is, in fact, the default loop, and false

								otherwise.


								=item unsigned int ev_iteration (loop)


								Returns the current iteration count for the event loop, which is identical

								to the number of times libev did poll for new events. It starts at C<0>

								and happily wraps around with enough iterations.


								This value can sometimes be useful as a generation counter of sorts (it

								"ticks" the number of loop iterations), as it roughly corresponds with

								C<ev_prepare> and C<ev_check> calls - and is incremented between the

								prepare and check phases.


								=item unsigned int ev_depth (loop)


								Returns the number of times C<ev_run> was entered minus the number of

								times C<ev_run> was exited normally, in other words, the recursion depth.


								Outside C<ev_run>, this number is zero. In a callback, this number is

								C<1>, unless C<ev_run> was invoked recursively (or from another thread),

								in which case it is higher.


								Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,

								throwing an exception etc.), doesn't count as "exit" - consider this

								as a hint to avoid such ungentleman-like behaviour unless it's really

								convenient, in which case it is fully supported.


								=item unsigned int ev_backend (loop)


								Returns one of the C<EVBACKEND_*> flags indicating the event backend in

								use.


								=item ev_tstamp ev_now (loop)


								Returns the current "event loop time", which is the time the event loop

								received events and started processing them. This timestamp does not

								change as long as callbacks are being processed, and this is also the base

								time used for relative timers. You can treat it as the timestamp of the

								event occurring (or more correctly, libev finding out about it).


								=item ev_now_update (loop)


								Establishes the current time by querying the kernel, updating the time

								returned by C<ev_now ()> in the progress. This is a costly operation and

								is usually done automatically within C<ev_run ()>.


								This function is rarely useful, but when some event callback runs for a

								very long time without entering the event loop, updating libev's idea of

								the current time is a good idea.


								See also L<The special problem of time updates> in the C<ev_timer> section.


								=item ev_suspend (loop)


								=item ev_resume (loop)


								These two functions suspend and resume an event loop, for use when the

								loop is not used for a while and timeouts should not be processed.


								A typical use case would be an interactive program such as a game:  When

								the user presses C<^Z> to suspend the game and resumes it an hour later it

								would be best to handle timeouts as if no time had actually passed while

								the program was suspended. This can be achieved by calling C<ev_suspend>

								in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling

								C<ev_resume> directly afterwards to resume timer processing.


								Effectively, all C<ev_timer> watchers will be delayed by the time spend

								between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers

								will be rescheduled (that is, they will lose any events that would have

								occurred while suspended).


								After calling C<ev_suspend> you B<must not> call I<any> function on the

								given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>

								without a previous call to C<ev_suspend>.


								Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the

								event loop time (see C<ev_now_update>).


								=item ev_run (loop, int flags)


								Finally, this is it, the event handler. This function usually is called

								after you have initialised all your watchers and you want to start

								handling events. It will ask the operating system for any new events, call

								the watcher callbacks, an then repeat the whole process indefinitely: This

								is why event loops are called I<loops>.


								If the flags argument is specified as C<0>, it will keep handling events

								until either no event watchers are active anymore or C<ev_break> was

								called.


								Please note that an explicit C<ev_break> is usually better than

								relying on all watchers to be stopped when deciding when a program has

								finished (especially in interactive programs), but having a program

								that automatically loops as long as it has to and no longer by virtue

								of relying on its watchers stopping correctly, that is truly a thing of

								beauty.


								This function is also I<mostly> exception-safe - you can break out of

								a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++

								exception and so on. This does not decrement the C<ev_depth> value, nor

								will it clear any outstanding C<EVBREAK_ONE> breaks.


								A flags value of C<EVRUN_NOWAIT> will look for new events, will handle

								those events and any already outstanding ones, but will not wait and

								block your process in case there are no events and will return after one

								iteration of the loop. This is sometimes useful to poll and handle new

								events while doing lengthy calculations, to keep the program responsive.


								A flags value of C<EVRUN_ONCE> will look for new events (waiting if

								necessary) and will handle those and any already outstanding ones. It

								will block your process until at least one new event arrives (which could

								be an event internal to libev itself, so there is no guarantee that a

								user-registered callback will be called), and will return after one

								iteration of the loop.


								This is useful if you are waiting for some external event in conjunction

								with something not expressible using other libev watchers (i.e. "roll your

								own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is

								usually a better approach for this kind of thing.


								Here are the gory details of what C<ev_run> does:


								   - Increment loop depth.

								   - Reset the ev_break status.

								   - Before the first iteration, call any pending watchers.

								   LOOP:

								   - If EVFLAG_FORKCHECK was used, check for a fork.

								   - If a fork was detected (by any means), queue and call all fork watchers.

								   - Queue and call all prepare watchers.

								   - If ev_break was called, goto FINISH.

								   - If we have been forked, detach and recreate the kernel state

								     as to not disturb the other process.

								   - Update the kernel state with all outstanding changes.

								   - Update the "event loop time" (ev_now ()).

								   - Calculate for how long to sleep or block, if at all

								     (active idle watchers, EVRUN_NOWAIT or not having

								     any active watchers at all will result in not sleeping).

								   - Sleep if the I/O and timer collect interval say so.

								   - Increment loop iteration counter.

								   - Block the process, waiting for any events.

								   - Queue all outstanding I/O (fd) events.

								   - Update the "event loop time" (ev_now ()), and do time jump adjustments.

								   - Queue all expired timers.

								   - Queue all expired periodics.

								   - Queue all idle watchers with priority higher than that of pending events.

								   - Queue all check watchers.

								   - Call all queued watchers in reverse order (i.e. check watchers first).

								     Signals and child watchers are implemented as I/O watchers, and will

								     be handled here by queueing them when their watcher gets executed.

								   - If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT

								     were used, or there are no active watchers, goto FINISH, otherwise

								     continue with step LOOP.

								   FINISH:

								   - Reset the ev_break status iff it was EVBREAK_ONE.

								   - Decrement the loop depth.

								   - Return.


								Example: Queue some jobs and then loop until no events are outstanding

								anymore.


								   ... queue jobs here, make sure they register event watchers as long

								   ... as they still have work to do (even an idle watcher will do..)

								   ev_run (my_loop, 0);

								   ... jobs done or somebody called break. yeah!


								=item ev_break (loop, how)


								Can be used to make a call to C<ev_run> return early (but only after it

								has processed all outstanding events). The C<how> argument must be either

								C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or

								C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.


								This "break state" will be cleared on the next call to C<ev_run>.


								It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in

								which case it will have no effect.


								=item ev_ref (loop)


								=item ev_unref (loop)


								Ref/unref can be used to add or remove a reference count on the event

								loop: Every watcher keeps one reference, and as long as the reference

								count is nonzero, C<ev_run> will not return on its own.


								This is useful when you have a watcher that you never intend to

								unregister, but that nevertheless should not keep C<ev_run> from

								returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>

								before stopping it.


								As an example, libev itself uses this for its internal signal pipe: It

								is not visible to the libev user and should not keep C<ev_run> from

								exiting if no event watchers registered by it are active. It is also an

								excellent way to do this for generic recurring timers or from within

								third-party libraries. Just remember to I<unref after start> and I<ref

								before stop> (but only if the watcher wasn't active before, or was active

								before, respectively. Note also that libev might stop watchers itself

								(e.g. non-repeating timers) in which case you have to C<ev_ref>

								in the callback).


								Example: Create a signal watcher, but keep it from keeping C<ev_run>

								running when nothing else is active.


								   ev_signal exitsig;

								   ev_signal_init (&exitsig, sig_cb, SIGINT);

								   ev_signal_start (loop, &exitsig);

								   ev_unref (loop);


								Example: For some weird reason, unregister the above signal handler again.


								   ev_ref (loop);

								   ev_signal_stop (loop, &exitsig);


								=item ev_set_io_collect_interval (loop, ev_tstamp interval)


								=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)


								These advanced functions influence the time that libev will spend waiting

								for events. Both time intervals are by default C<0>, meaning that libev

								will try to invoke timer/periodic callbacks and I/O callbacks with minimum

								latency.


								Setting these to a higher value (the C<interval> I<must> be >= C<0>)

								allows libev to delay invocation of I/O and timer/periodic callbacks

								to increase efficiency of loop iterations (or to increase power-saving

								opportunities).


								The idea is that sometimes your program runs just fast enough to handle

								one (or very few) event(s) per loop iteration. While this makes the

								program responsive, it also wastes a lot of CPU time to poll for new

								events, especially with backends like C<select ()> which have a high

								overhead for the actual polling but can deliver many events at once.


								By setting a higher I<io collect interval> you allow libev to spend more

								time collecting I/O events, so you can handle more events per iteration,

								at the cost of increasing latency. Timeouts (both C<ev_periodic> and

								C<ev_timer>) will be not affected. Setting this to a non-null value will

								introduce an additional C<ev_sleep ()> call into most loop iterations. The

								sleep time ensures that libev will not poll for I/O events more often then

								once per this interval, on average.


								Likewise, by setting a higher I<timeout collect interval> you allow libev

								to spend more time collecting timeouts, at the expense of increased

								latency/jitter/inexactness (the watcher callback will be called

								later). C<ev_io> watchers will not be affected. Setting this to a non-null

								value will not introduce any overhead in libev.


								Many (busy) programs can usually benefit by setting the I/O collect

								interval to a value near C<0.1> or so, which is often enough for

								interactive servers (of course not for games), likewise for timeouts. It

								usually doesn't make much sense to set it to a lower value than C<0.01>,

								as this approaches the timing granularity of most systems. Note that if

								you do transactions with the outside world and you can't increase the

								parallelity, then this setting will limit your transaction rate (if you

								need to poll once per transaction and the I/O collect interval is 0.01,

								then you can't do more than 100 transactions per second).


								Setting the I<timeout collect interval> can improve the opportunity for

								saving power, as the program will "bundle" timer callback invocations that

								are "near" in time together, by delaying some, thus reducing the number of

								times the process sleeps and wakes up again. Another useful technique to

								reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure

								they fire on, say, one-second boundaries only.


								Example: we only need 0.1s timeout granularity, and we wish not to poll

								more often than 100 times per second:


								   ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);

								   ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);


								=item ev_invoke_pending (loop)


								This call will simply invoke all pending watchers while resetting their

								pending state. Normally, C<ev_run> does this automatically when required,

								but when overriding the invoke callback this call comes handy. This

								function can be invoked from a watcher - this can be useful for example

								when you want to do some lengthy calculation and want to pass further

								event handling to another thread (you still have to make sure only one

								thread executes within C<ev_invoke_pending> or C<ev_run> of course).


								=item int ev_pending_count (loop)


								Returns the number of pending watchers - zero indicates that no watchers

								are pending.


								=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))


								This overrides the invoke pending functionality of the loop: Instead of

								invoking all pending watchers when there are any, C<ev_run> will call

								this callback instead. This is useful, for example, when you want to

								invoke the actual watchers inside another context (another thread etc.).


								If you want to reset the callback, use C<ev_invoke_pending> as new

								callback.


								=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))


								Sometimes you want to share the same loop between multiple threads. This

								can be done relatively simply by putting mutex_lock/unlock calls around

								each call to a libev function.


								However, C<ev_run> can run an indefinite time, so it is not feasible

								to wait for it to return. One way around this is to wake up the event

								loop via C<ev_break> and C<av_async_send>, another way is to set these

								I<release> and I<acquire> callbacks on the loop.


								When set, then C<release> will be called just before the thread is

								suspended waiting for new events, and C<acquire> is called just

								afterwards.


								Ideally, C<release> will just call your mutex_unlock function, and

								C<acquire> will just call the mutex_lock function again.


								While event loop modifications are allowed between invocations of

								C<release> and C<acquire> (that's their only purpose after all), no

								modifications done will affect the event loop, i.e. adding watchers will

								have no effect on the set of file descriptors being watched, or the time

								waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it

								to take note of any changes you made.


								In theory, threads executing C<ev_run> will be async-cancel safe between

								invocations of C<release> and C<acquire>.


								See also the locking example in the C<THREADS> section later in this

								document.


								=item ev_set_userdata (loop, void *data)


								=item void *ev_userdata (loop)


								Set and retrieve a single C<void *> associated with a loop. When

								C<ev_set_userdata> has never been called, then C<ev_userdata> returns

								C<0>.


								These two functions can be used to associate arbitrary data with a loop,

								and are intended solely for the C<invoke_pending_cb>, C<release> and

								C<acquire> callbacks described above, but of course can be (ab-)used for

								any other purpose as well.


								=item ev_verify (loop)


								This function only does something when C<EV_VERIFY> support has been

								compiled in, which is the default for non-minimal builds. It tries to go

								through all internal structures and checks them for validity. If anything

								is found to be inconsistent, it will print an error message to standard

								error and call C<abort ()>.


								This can be used to catch bugs inside libev itself: under normal

								circumstances, this function will never abort as of course libev keeps its

								data structures consistent.


								=back


								=head1 ANATOMY OF A WATCHER


								In the following description, uppercase C<TYPE> in names stands for the

								watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer

								watchers and C<ev_io_start> for I/O watchers.


								A watcher is an opaque structure that you allocate and register to record

								your interest in some event. To make a concrete example, imagine you want

								to wait for STDIN to become readable, you would create an C<ev_io> watcher

								for that:


								   static void my_cb (struct ev_loop *loop, ev_io *w, int revents)

								   {

								     ev_io_stop (w);

								     ev_break (loop, EVBREAK_ALL);

								   }


								   struct ev_loop *loop = ev_default_loop (0);


								   ev_io stdin_watcher;


								   ev_init (&stdin_watcher, my_cb);

								   ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);

								   ev_io_start (loop, &stdin_watcher);


								   ev_run (loop, 0);


								As you can see, you are responsible for allocating the memory for your

								watcher structures (and it is I<usually> a bad idea to do this on the

								stack).


								Each watcher has an associated watcher structure (called C<struct ev_TYPE>

								or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).


								Each watcher structure must be initialised by a call to C<ev_init (watcher

								*, callback)>, which expects a callback to be provided. This callback is

								invoked each time the event occurs (or, in the case of I/O watchers, each

								time the event loop detects that the file descriptor given is readable

								and/or writable).


								Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>

								macro to configure it, with arguments specific to the watcher type. There

								is also a macro to combine initialisation and setting in one call: C<<

								ev_TYPE_init (watcher *, callback, ...) >>.


								To make the watcher actually watch out for events, you have to start it

								with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher

								*) >>), and you can stop watching for events at any time by calling the

								corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.


								As long as your watcher is active (has been started but not stopped) you

								must not touch the values stored in it. Most specifically you must never

								reinitialise it or call its C<ev_TYPE_set> macro.


								Each and every callback receives the event loop pointer as first, the

								registered watcher structure as second, and a bitset of received events as

								third argument.


								The received events usually include a single bit per event type received

								(you can receive multiple events at the same time). The possible bit masks

								are:


								=over 4


								=item C<EV_READ>


								=item C<EV_WRITE>


								The file descriptor in the C<ev_io> watcher has become readable and/or

								writable.


								=item C<EV_TIMER>


								The C<ev_timer> watcher has timed out.


								=item C<EV_PERIODIC>


								The C<ev_periodic> watcher has timed out.


								=item C<EV_SIGNAL>


								The signal specified in the C<ev_signal> watcher has been received by a thread.


								=item C<EV_CHILD>


								The pid specified in the C<ev_child> watcher has received a status change.


								=item C<EV_STAT>


								The path specified in the C<ev_stat> watcher changed its attributes somehow.


								=item C<EV_IDLE>


								The C<ev_idle> watcher has determined that you have nothing better to do.


								=item C<EV_PREPARE>


								=item C<EV_CHECK>


								All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts

								to gather new events, and all C<ev_check> watchers are invoked just after

								C<ev_run> has gathered them, but before it invokes any callbacks for any

								received events. Callbacks of both watcher types can start and stop as

								many watchers as they want, and all of them will be taken into account

								(for example, a C<ev_prepare> watcher might start an idle watcher to keep

								C<ev_run> from blocking).


								=item C<EV_EMBED>


								The embedded event loop specified in the C<ev_embed> watcher needs attention.


								=item C<EV_FORK>


								The event loop has been resumed in the child process after fork (see

								C<ev_fork>).


								=item C<EV_CLEANUP>


								The event loop is about to be destroyed (see C<ev_cleanup>).


								=item C<EV_ASYNC>


								The given async watcher has been asynchronously notified (see C<ev_async>).


								=item C<EV_CUSTOM>


								Not ever sent (or otherwise used) by libev itself, but can be freely used

								by libev users to signal watchers (e.g. via C<ev_feed_event>).


								=item C<EV_ERROR>


								An unspecified error has occurred, the watcher has been stopped. This might

								happen because the watcher could not be properly started because libev

								ran out of memory, a file descriptor was found to be closed or any other

								problem. Libev considers these application bugs.


								You best act on it by reporting the problem and somehow coping with the

								watcher being stopped. Note that well-written programs should not receive

								an error ever, so when your watcher receives it, this usually indicates a

								bug in your program.


								Libev will usually signal a few "dummy" events together with an error, for

								example it might indicate that a fd is readable or writable, and if your

								callbacks is well-written it can just attempt the operation and cope with

								the error from read() or write(). This will not work in multi-threaded

								programs, though, as the fd could already be closed and reused for another

								thing, so beware.


								=back


								=head2 GENERIC WATCHER FUNCTIONS


								=over 4


								=item C<ev_init> (ev_TYPE *watcher, callback)


								This macro initialises the generic portion of a watcher. The contents

								of the watcher object can be arbitrary (so C<malloc> will do). Only

								the generic parts of the watcher are initialised, you I<need> to call

								the type-specific C<ev_TYPE_set> macro afterwards to initialise the

								type-specific parts. For each type there is also a C<ev_TYPE_init> macro

								which rolls both calls into one.


								You can reinitialise a watcher at any time as long as it has been stopped

								(or never started) and there are no pending events outstanding.


								The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,

								int revents)>.


								Example: Initialise an C<ev_io> watcher in two steps.


								   ev_io w;

								   ev_init (&w, my_cb);

								   ev_io_set (&w, STDIN_FILENO, EV_READ);


								=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])


								This macro initialises the type-specific parts of a watcher. You need to

								call C<ev_init> at least once before you call this macro, but you can

								call C<ev_TYPE_set> any number of times. You must not, however, call this

								macro on a watcher that is active (it can be pending, however, which is a

								difference to the C<ev_init> macro).


								Although some watcher types do not have type-specific arguments

								(e.g. C<ev_prepare>) you still need to call its C<set> macro.


								See C<ev_init>, above, for an example.


								=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])


								This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro

								calls into a single call. This is the most convenient method to initialise

								a watcher. The same limitations apply, of course.


								Example: Initialise and set an C<ev_io> watcher in one step.


								   ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);


								=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)


								Starts (activates) the given watcher. Only active watchers will receive

								events. If the watcher is already active nothing will happen.


								Example: Start the C<ev_io> watcher that is being abused as example in this

								whole section.


								   ev_io_start (EV_DEFAULT_UC, &w);


								=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)


								Stops the given watcher if active, and clears the pending status (whether

								the watcher was active or not).


								It is possible that stopped watchers are pending - for example,

								non-repeating timers are being stopped when they become pending - but

								calling C<ev_TYPE_stop> ensures that the watcher is neither active nor

								pending. If you want to free or reuse the memory used by the watcher it is

								therefore a good idea to always call its C<ev_TYPE_stop> function.


								=item bool ev_is_active (ev_TYPE *watcher)


								Returns a true value iff the watcher is active (i.e. it has been started

								and not yet been stopped). As long as a watcher is active you must not modify

								it.


								=item bool ev_is_pending (ev_TYPE *watcher)


								Returns a true value iff the watcher is pending, (i.e. it has outstanding

								events but its callback has not yet been invoked). As long as a watcher

								is pending (but not active) you must not call an init function on it (but

								C<ev_TYPE_set> is safe), you must not change its priority, and you must

								make sure the watcher is available to libev (e.g. you cannot C<free ()>

								it).


								=item callback ev_cb (ev_TYPE *watcher)


								Returns the callback currently set on the watcher.


								=item ev_cb_set (ev_TYPE *watcher, callback)


								Change the callback. You can change the callback at virtually any time

								(modulo threads).


								=item ev_set_priority (ev_TYPE *watcher, int priority)


								=item int ev_priority (ev_TYPE *watcher)


								Set and query the priority of the watcher. The priority is a small

								integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>

								(default: C<-2>). Pending watchers with higher priority will be invoked

								before watchers with lower priority, but priority will not keep watchers

								from being executed (except for C<ev_idle> watchers).


								If you need to suppress invocation when higher priority events are pending

								you need to look at C<ev_idle> watchers, which provide this functionality.


								You I<must not> change the priority of a watcher as long as it is active or

								pending.


								Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is

								fine, as long as you do not mind that the priority value you query might

								or might not have been clamped to the valid range.


								The default priority used by watchers when no priority has been set is

								always C<0>, which is supposed to not be too high and not be too low :).


								See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of

								priorities.


								=item ev_invoke (loop, ev_TYPE *watcher, int revents)


								Invoke the C<watcher> with the given C<loop> and C<revents>. Neither

								C<loop> nor C<revents> need to be valid as long as the watcher callback

								can deal with that fact, as both are simply passed through to the

								callback.


								=item int ev_clear_pending (loop, ev_TYPE *watcher)


								If the watcher is pending, this function clears its pending status and

								returns its C<revents> bitset (as if its callback was invoked). If the

								watcher isn't pending it does nothing and returns C<0>.


								Sometimes it can be useful to "poll" a watcher instead of waiting for its

								callback to be invoked, which can be accomplished with this function.


								=item ev_feed_event (loop, ev_TYPE *watcher, int revents)


								Feeds the given event set into the event loop, as if the specified event

								had happened for the specified watcher (which must be a pointer to an

								initialised but not necessarily started event watcher). Obviously you must

								not free the watcher as long as it has pending events.


								Stopping the watcher, letting libev invoke it, or calling

								C<ev_clear_pending> will clear the pending event, even if the watcher was

								not started in the first place.


								See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related

								functions that do not need a watcher.


								=back


								See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR

								OWN COMPOSITE WATCHERS> idioms.


								=head2 WATCHER STATES


								There are various watcher states mentioned throughout this manual -

								active, pending and so on. In this section these states and the rules to

								transition between them will be described in more detail - and while these

								rules might look complicated, they usually do "the right thing".


								=over 4


								=item initialiased


								Before a watcher can be registered with the event looop it has to be

								initialised. This can be done with a call to C<ev_TYPE_init>, or calls to

								C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.


								In this state it is simply some block of memory that is suitable for

								use in an event loop. It can be moved around, freed, reused etc. at

								will - as long as you either keep the memory contents intact, or call

								C<ev_TYPE_init> again.


								=item started/running/active


								Once a watcher has been started with a call to C<ev_TYPE_start> it becomes

								property of the event loop, and is actively waiting for events. While in

								this state it cannot be accessed (except in a few documented ways), moved,

								freed or anything else - the only legal thing is to keep a pointer to it,

								and call libev functions on it that are documented to work on active watchers.


								=item pending


								If a watcher is active and libev determines that an event it is interested

								in has occurred (such as a timer expiring), it will become pending. It will

								stay in this pending state until either it is stopped or its callback is

								about to be invoked, so it is not normally pending inside the watcher

								callback.


								The watcher might or might not be active while it is pending (for example,

								an expired non-repeating timer can be pending but no longer active). If it

								is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),

								but it is still property of the event loop at this time, so cannot be

								moved, freed or reused. And if it is active the rules described in the

								previous item still apply.


								It is also possible to feed an event on a watcher that is not active (e.g.

								via C<ev_feed_event>), in which case it becomes pending without being

								active.


								=item stopped


								A watcher can be stopped implicitly by libev (in which case it might still

								be pending), or explicitly by calling its C<ev_TYPE_stop> function. The

								latter will clear any pending state the watcher might be in, regardless

								of whether it was active or not, so stopping a watcher explicitly before

								freeing it is often a good idea.


								While stopped (and not pending) the watcher is essentially in the

								initialised state, that is, it can be reused, moved, modified in any way

								you wish (but when you trash the memory block, you need to C<ev_TYPE_init>

								it again).


								=back


								=head2 WATCHER PRIORITY MODELS


								Many event loops support I<watcher priorities>, which are usually small

								integers that influence the ordering of event callback invocation

								between watchers in some way, all else being equal.


								In libev, Watcher priorities can be set using C<ev_set_priority>. See its

								description for the more technical details such as the actual priority

								range.


								There are two common ways how these these priorities are being interpreted

								by event loops:


								In the more common lock-out model, higher priorities "lock out" invocation

								of lower priority watchers, which means as long as higher priority

								watchers receive events, lower priority watchers are not being invoked.


								The less common only-for-ordering model uses priorities solely to order

								callback invocation within a single event loop iteration: Higher priority

								watchers are invoked before lower priority ones, but they all get invoked

								before polling for new events.


								Libev uses the second (only-for-ordering) model for all its watchers

								except for idle watchers (which use the lock-out model).


								The rationale behind this is that implementing the lock-out model for

								watchers is not well supported by most kernel interfaces, and most event

								libraries will just poll for the same events again and again as long as

								their callbacks have not been executed, which is very inefficient in the

								common case of one high-priority watcher locking out a mass of lower

								priority ones.


								Static (ordering) priorities are most useful when you have two or more

								watchers handling the same resource: a typical usage example is having an

								C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle

								timeouts. Under load, data might be received while the program handles

								other jobs, but since timers normally get invoked first, the timeout

								handler will be executed before checking for data. In that case, giving

								the timer a lower priority than the I/O watcher ensures that I/O will be

								handled first even under adverse conditions (which is usually, but not

								always, what you want).


								Since idle watchers use the "lock-out" model, meaning that idle watchers

								will only be executed when no same or higher priority watchers have

								received events, they can be used to implement the "lock-out" model when

								required.


								For example, to emulate how many other event libraries handle priorities,

								you can associate an C<ev_idle> watcher to each such watcher, and in

								the normal watcher callback, you just start the idle watcher. The real

								processing is done in the idle watcher callback. This causes libev to

								continuously poll and process kernel event data for the watcher, but when

								the lock-out case is known to be rare (which in turn is rare :), this is

								workable.


								Usually, however, the lock-out model implemented that way will perform

								miserably under the type of load it was designed to handle. In that case,

								it might be preferable to stop the real watcher before starting the

								idle watcher, so the kernel will not have to process the event in case

								the actual processing will be delayed for considerable time.


								Here is an example of an I/O watcher that should run at a strictly lower

								priority than the default, and which should only process data when no

								other events are pending:


								   ev_idle idle; // actual processing watcher

								   ev_io io;     // actual event watcher


								   static void

								   io_cb (EV_P_ ev_io *w, int revents)

								   {

								     // stop the I/O watcher, we received the event, but

								     // are not yet ready to handle it.

								     ev_io_stop (EV_A_ w);


								     // start the idle watcher to handle the actual event.

								     // it will not be executed as long as other watchers

								     // with the default priority are receiving events.

								     ev_idle_start (EV_A_ &idle);

								   }


								   static void

								   idle_cb (EV_P_ ev_idle *w, int revents)

								   {

								     // actual processing

								     read (STDIN_FILENO, ...);


								     // have to start the I/O watcher again, as

								     // we have handled the event

								     ev_io_start (EV_P_ &io);

								   }


								   // initialisation

								   ev_idle_init (&idle, idle_cb);

								   ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);

								   ev_io_start (EV_DEFAULT_ &io);


								In the "real" world, it might also be beneficial to start a timer, so that

								low-priority connections can not be locked out forever under load. This

								enables your program to keep a lower latency for important connections

								during short periods of high load, while not completely locking out less

								important ones.


								=head1 WATCHER TYPES


								This section describes each watcher in detail, but will not repeat

								information given in the last section. Any initialisation/set macros,

								functions and members specific to the watcher type are explained.


								Members are additionally marked with either I<[read-only]>, meaning that,

								while the watcher is active, you can look at the member and expect some

								sensible content, but you must not modify it (you can modify it while the

								watcher is stopped to your hearts content), or I<[read-write]>, which

								means you can expect it to have some sensible content while the watcher

								is active, but you can also modify it. Modifying it may not do something

								sensible or take immediate effect (or do anything at all), but libev will

								not crash or malfunction in any way.


								=head2 C<ev_io> - is this file descriptor readable or writable?


								I/O watchers check whether a file descriptor is readable or writable

								in each iteration of the event loop, or, more precisely, when reading

								would not block the process and writing would at least be able to write

								some data. This behaviour is called level-triggering because you keep

								receiving events as long as the condition persists. Remember you can stop

								the watcher if you don't want to act on the event and neither want to

								receive future events.


								In general you can register as many read and/or write event watchers per

								fd as you want (as long as you don't confuse yourself). Setting all file

								descriptors to non-blocking mode is also usually a good idea (but not

								required if you know what you are doing).


								Another thing you have to watch out for is that it is quite easy to

								receive "spurious" readiness notifications, that is, your callback might

								be called with C<EV_READ> but a subsequent C<read>(2) will actually block

								because there is no data. It is very easy to get into this situation even

								with a relatively standard program structure. Thus it is best to always

								use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far

								preferable to a program hanging until some data arrives.


								If you cannot run the fd in non-blocking mode (for example you should

								not play around with an Xlib connection), then you have to separately

								re-test whether a file descriptor is really ready with a known-to-be good

								interface such as poll (fortunately in the case of Xlib, it already does

								this on its own, so its quite safe to use). Some people additionally

								use C<SIGALRM> and an interval timer, just to be sure you won't block

								indefinitely.


								But really, best use non-blocking mode.


								=head3 The special problem of disappearing file descriptors


								Some backends (e.g. kqueue, epoll) need to be told about closing a file

								descriptor (either due to calling C<close> explicitly or any other means,

								such as C<dup2>). The reason is that you register interest in some file

								descriptor, but when it goes away, the operating system will silently drop

								this interest. If another file descriptor with the same number then is

								registered with libev, there is no efficient way to see that this is, in

								fact, a different file descriptor.


								To avoid having to explicitly tell libev about such cases, libev follows

								the following policy:  Each time C<ev_io_set> is being called, libev

								will assume that this is potentially a new file descriptor, otherwise

								it is assumed that the file descriptor stays the same. That means that

								you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the

								descriptor even if the file descriptor number itself did not change.


								This is how one would do it normally anyway, the important point is that

								the libev application should not optimise around libev but should leave

								optimisations to libev.


								=head3 The special problem of dup'ed file descriptors


								Some backends (e.g. epoll), cannot register events for file descriptors,

								but only events for the underlying file descriptions. That means when you

								have C<dup ()>'ed file descriptors or weirder constellations, and register

								events for them, only one file descriptor might actually receive events.


								There is no workaround possible except not registering events

								for potentially C<dup ()>'ed file descriptors, or to resort to

								C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.


								=head3 The special problem of files


								Many people try to use C<select> (or libev) on file descriptors

								representing files, and expect it to become ready when their program

								doesn't block on disk accesses (which can take a long time on their own).


								However, this cannot ever work in the "expected" way - you get a readiness

								notification as soon as the kernel knows whether and how much data is

								there, and in the case of open files, that's always the case, so you

								always get a readiness notification instantly, and your read (or possibly

								write) will still block on the disk I/O.


								Another way to view it is that in the case of sockets, pipes, character

								devices and so on, there is another party (the sender) that delivers data

								on its own, but in the case of files, there is no such thing: the disk

								will not send data on its own, simply because it doesn't know what you

								wish to read - you would first have to request some data.


								Since files are typically not-so-well supported by advanced notification

								mechanism, libev tries hard to emulate POSIX behaviour with respect

								to files, even though you should not use it. The reason for this is

								convenience: sometimes you want to watch STDIN or STDOUT, which is

								usually a tty, often a pipe, but also sometimes files or special devices

								(for example, C<epoll> on Linux works with F</dev/random> but not with

								F</dev/urandom>), and even though the file might better be served with

								asynchronous I/O instead of with non-blocking I/O, it is still useful when

								it "just works" instead of freezing.


								So avoid file descriptors pointing to files when you know it (e.g. use

								libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or

								when you rarely read from a file instead of from a socket, and want to

								reuse the same code path.


								=head3 The special problem of fork


								Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit

								useless behaviour. Libev fully supports fork, but needs to be told about

								it in the child if you want to continue to use it in the child.


								To support fork in your child processes, you have to call C<ev_loop_fork

								()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to

								C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.


								=head3 The special problem of SIGPIPE


								While not really specific to libev, it is easy to forget about C<SIGPIPE>:

								when writing to a pipe whose other end has been closed, your program gets

								sent a SIGPIPE, which, by default, aborts your program. For most programs

								this is sensible behaviour, for daemons, this is usually undesirable.


								So when you encounter spurious, unexplained daemon exits, make sure you

								ignore SIGPIPE (and maybe make sure you log the exit status of your daemon

								somewhere, as that would have given you a big clue).


								=head3 The special problem of accept()ing when you can't


								Many implementations of the POSIX C<accept> function (for example,

								found in post-2004 Linux) have the peculiar behaviour of not removing a

								connection from the pending queue in all error cases.


								For example, larger servers often run out of file descriptors (because

								of resource limits), causing C<accept> to fail with C<ENFILE> but not

								rejecting the connection, leading to libev signalling readiness on

								the next iteration again (the connection still exists after all), and

								typically causing the program to loop at 100% CPU usage.


								Unfortunately, the set of errors that cause this issue differs between

								operating systems, there is usually little the app can do to remedy the

								situation, and no known thread-safe method of removing the connection to

								cope with overload is known (to me).


								One of the easiest ways to handle this situation is to just ignore it

								- when the program encounters an overload, it will just loop until the

								situation is over. While this is a form of busy waiting, no OS offers an

								event-based way to handle this situation, so it's the best one can do.


								A better way to handle the situation is to log any errors other than

								C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such

								messages, and continue as usual, which at least gives the user an idea of

								what could be wrong ("raise the ulimit!"). For extra points one could stop

								the C<ev_io> watcher on the listening fd "for a while", which reduces CPU

								usage.


								If your program is single-threaded, then you could also keep a dummy file

								descriptor for overload situations (e.g. by opening F</dev/null>), and

								when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,

								close that fd, and create a new dummy fd. This will gracefully refuse

								clients under typical overload conditions.


								The last way to handle it is to simply log the error and C<exit>, as

								is often done with C<malloc> failures, but this results in an easy

								opportunity for a DoS attack.


								=head3 Watcher-Specific Functions


								=over 4


								=item ev_io_init (ev_io *, callback, int fd, int events)


								=item ev_io_set (ev_io *, int fd, int events)


								Configures an C<ev_io> watcher. The C<fd> is the file descriptor to

								receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or

								C<EV_READ | EV_WRITE>, to express the desire to receive the given events.


								=item int fd [read-only]


								The file descriptor being watched.


								=item int events [read-only]


								The events being watched.


								=back


								=head3 Examples


								Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well

								readable, but only once. Since it is likely line-buffered, you could

								attempt to read a whole line in the callback.


								   static void

								   stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)

								   {

								      ev_io_stop (loop, w);

								     .. read from stdin here (or from w->fd) and handle any I/O errors

								   }


								   ...

								   struct ev_loop *loop = ev_default_init (0);

								   ev_io stdin_readable;

								   ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);

								   ev_io_start (loop, &stdin_readable);

								   ev_run (loop, 0);


								=head2 C<ev_timer> - relative and optionally repeating timeouts


								Timer watchers are simple relative timers that generate an event after a

								given time, and optionally repeating in regular intervals after that.


								The timers are based on real time, that is, if you register an event that

								times out after an hour and you reset your system clock to January last

								year, it will still time out after (roughly) one hour. "Roughly" because

								detecting time jumps is hard, and some inaccuracies are unavoidable (the

								monotonic clock option helps a lot here).


								The callback is guaranteed to be invoked only I<after> its timeout has

								passed (not I<at>, so on systems with very low-resolution clocks this

								might introduce a small delay). If multiple timers become ready during the

								same loop iteration then the ones with earlier time-out values are invoked

								before ones of the same priority with later time-out values (but this is

								no longer true when a callback calls C<ev_run> recursively).


								=head3 Be smart about timeouts


								Many real-world problems involve some kind of timeout, usually for error

								recovery. A typical example is an HTTP request - if the other side hangs,

								you want to raise some error after a while.


								What follows are some ways to handle this problem, from obvious and

								inefficient to smart and efficient.


								In the following, a 60 second activity timeout is assumed - a timeout that

								gets reset to 60 seconds each time there is activity (e.g. each time some

								data or other life sign was received).


								=over 4


								=item 1. Use a timer and stop, reinitialise and start it on activity.


								This is the most obvious, but not the most simple way: In the beginning,

								start the watcher:


								   ev_timer_init (timer, callback, 60., 0.);

								   ev_timer_start (loop, timer);


								Then, each time there is some activity, C<ev_timer_stop> it, initialise it

								and start it again:


								   ev_timer_stop (loop, timer);

								   ev_timer_set (timer, 60., 0.);

								   ev_timer_start (loop, timer);


								This is relatively simple to implement, but means that each time there is

								some activity, libev will first have to remove the timer from its internal

								data structure and then add it again. Libev tries to be fast, but it's

								still not a constant-time operation.


								=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.


								This is the easiest way, and involves using C<ev_timer_again> instead of

								C<ev_timer_start>.


								To implement this, configure an C<ev_timer> with a C<repeat> value

								of C<60> and then call C<ev_timer_again> at start and each time you

								successfully read or write some data. If you go into an idle state where

								you do not expect data to travel on the socket, you can C<ev_timer_stop>

								the timer, and C<ev_timer_again> will automatically restart it if need be.


								That means you can ignore both the C<ev_timer_start> function and the

								C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>

								member and C<ev_timer_again>.


								At start:


								   ev_init (timer, callback);

								   timer->repeat = 60.;

								   ev_timer_again (loop, timer);


								Each time there is some activity:


								   ev_timer_again (loop, timer);


								It is even possible to change the time-out on the fly, regardless of

								whether the watcher is active or not:


								   timer->repeat = 30.;

								   ev_timer_again (loop, timer);


								This is slightly more efficient then stopping/starting the timer each time

								you want to modify its timeout value, as libev does not have to completely

								remove and re-insert the timer from/into its internal data structure.


								It is, however, even simpler than the "obvious" way to do it.


								=item 3. Let the timer time out, but then re-arm it as required.


								This method is more tricky, but usually most efficient: Most timeouts are

								relatively long compared to the intervals between other activity - in

								our example, within 60 seconds, there are usually many I/O events with

								associated activity resets.


								In this case, it would be more efficient to leave the C<ev_timer> alone,

								but remember the time of last activity, and check for a real timeout only

								within the callback:


								   ev_tstamp last_activity; // time of last activity


								   static void

								   callback (EV_P_ ev_timer *w, int revents)

								   {

								     ev_tstamp now     = ev_now (EV_A);

								     ev_tstamp timeout = last_activity + 60.;


								     // if last_activity + 60. is older than now, we did time out

								     if (timeout < now)

								       {

								         // timeout occurred, take action

								       }

								     else

								       {

								         // callback was invoked, but there was some activity, re-arm

								         // the watcher to fire in last_activity + 60, which is

								         // guaranteed to be in the future, so "again" is positive:

								         w->repeat = timeout - now;

								         ev_timer_again (EV_A_ w);

								       }

								   }


								To summarise the callback: first calculate the real timeout (defined

								as "60 seconds after the last activity"), then check if that time has

								been reached, which means something I<did>, in fact, time out. Otherwise

								the callback was invoked too early (C<timeout> is in the future), so

								re-schedule the timer to fire at that future time, to see if maybe we have

								a timeout then.


								Note how C<ev_timer_again> is used, taking advantage of the

								C<ev_timer_again> optimisation when the timer is already running.


								This scheme causes more callback invocations (about one every 60 seconds

								minus half the average time between activity), but virtually no calls to

								libev to change the timeout.


								To start the timer, simply initialise the watcher and set C<last_activity>

								to the current time (meaning we just have some activity :), then call the

								callback, which will "do the right thing" and start the timer:


								   ev_init (timer, callback);

								   last_activity = ev_now (loop);

								   callback (loop, timer, EV_TIMER);


								And when there is some activity, simply store the current time in

								C<last_activity>, no libev calls at all:


								   last_activity = ev_now (loop);


								This technique is slightly more complex, but in most cases where the

								time-out is unlikely to be triggered, much more efficient.


								Changing the timeout is trivial as well (if it isn't hard-coded in the

								callback :) - just change the timeout and invoke the callback, which will

								fix things for you.


								=item 4. Wee, just use a double-linked list for your timeouts.


								If there is not one request, but many thousands (millions...), all

								employing some kind of timeout with the same timeout value, then one can

								do even better:


								When starting the timeout, calculate the timeout value and put the timeout

								at the I<end> of the list.


								Then use an C<ev_timer> to fire when the timeout at the I<beginning> of

								the list is expected to fire (for example, using the technique #3).


								When there is some activity, remove the timer from the list, recalculate

								the timeout, append it to the end of the list again, and make sure to

								update the C<ev_timer> if it was taken from the beginning of the list.


								This way, one can manage an unlimited number of timeouts in O(1) time for

								starting, stopping and updating the timers, at the expense of a major

								complication, and having to use a constant timeout. The constant timeout

								ensures that the list stays sorted.


								=back


								So which method the best?


								Method #2 is a simple no-brain-required solution that is adequate in most

								situations. Method #3 requires a bit more thinking, but handles many cases

								better, and isn't very complicated either. In most case, choosing either

								one is fine, with #3 being better in typical situations.


								Method #1 is almost always a bad idea, and buys you nothing. Method #4 is

								rather complicated, but extremely efficient, something that really pays

								off after the first million or so of active timers, i.e. it's usually

								overkill :)


								=head3 The special problem of time updates


								Establishing the current time is a costly operation (it usually takes at

								least two system calls): EV therefore updates its idea of the current

								time only before and after C<ev_run> collects new events, which causes a

								growing difference between C<ev_now ()> and C<ev_time ()> when handling

								lots of events in one iteration.


								The relative timeouts are calculated relative to the C<ev_now ()>

								time. This is usually the right thing as this timestamp refers to the time

								of the event triggering whatever timeout you are modifying/starting. If

								you suspect event processing to be delayed and you I<need> to base the

								timeout on the current time, use something like this to adjust for this:


								   ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);


								If the event loop is suspended for a long time, you can also force an

								update of the time returned by C<ev_now ()> by calling C<ev_now_update

								()>.


								=head3 The special problems of suspended animation


								When you leave the server world it is quite customary to hit machines that

								can suspend/hibernate - what happens to the clocks during such a suspend?


								Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes

								all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue

								to run until the system is suspended, but they will not advance while the

								system is suspended. That means, on resume, it will be as if the program

								was frozen for a few seconds, but the suspend time will not be counted

								towards C<ev_timer> when a monotonic clock source is used. The real time

								clock advanced as expected, but if it is used as sole clocksource, then a

								long suspend would be detected as a time jump by libev, and timers would

								be adjusted accordingly.


								I would not be surprised to see different behaviour in different between

								operating systems, OS versions or even different hardware.


								The other form of suspend (job control, or sending a SIGSTOP) will see a

								time jump in the monotonic clocks and the realtime clock. If the program

								is suspended for a very long time, and monotonic clock sources are in use,

								then you can expect C<ev_timer>s to expire as the full suspension time

								will be counted towards the timers. When no monotonic clock source is in

								use, then libev will again assume a timejump and adjust accordingly.


								It might be beneficial for this latter case to call C<ev_suspend>

								and C<ev_resume> in code that handles C<SIGTSTP>, to at least get

								deterministic behaviour in this case (you can do nothing against

								C<SIGSTOP>).


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)


								=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)


								Configure the timer to trigger after C<after> seconds. If C<repeat>

								is C<0.>, then it will automatically be stopped once the timeout is

								reached. If it is positive, then the timer will automatically be

								configured to trigger again C<repeat> seconds later, again, and again,

								until stopped manually.


								The timer itself will do a best-effort at avoiding drift, that is, if

								you configure a timer to trigger every 10 seconds, then it will normally

								trigger at exactly 10 second intervals. If, however, your program cannot

								keep up with the timer (because it takes longer than those 10 seconds to

								do stuff) the timer will not fire more than once per event loop iteration.


								=item ev_timer_again (loop, ev_timer *)


								This will act as if the timer timed out and restart it again if it is

								repeating. The exact semantics are:


								If the timer is pending, its pending status is cleared.


								If the timer is started but non-repeating, stop it (as if it timed out).


								If the timer is repeating, either start it if necessary (with the

								C<repeat> value), or reset the running timer to the C<repeat> value.


								This sounds a bit complicated, see L<Be smart about timeouts>, above, for a

								usage example.


								=item ev_tstamp ev_timer_remaining (loop, ev_timer *)


								Returns the remaining time until a timer fires. If the timer is active,

								then this time is relative to the current event loop time, otherwise it's

								the timeout value currently configured.


								That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns

								C<5>. When the timer is started and one second passes, C<ev_timer_remaining>

								will return C<4>. When the timer expires and is restarted, it will return

								roughly C<7> (likely slightly less as callback invocation takes some time,

								too), and so on.


								=item ev_tstamp repeat [read-write]


								The current C<repeat> value. Will be used each time the watcher times out

								or C<ev_timer_again> is called, and determines the next timeout (if any),

								which is also when any modifications are taken into account.


								=back


								=head3 Examples


								Example: Create a timer that fires after 60 seconds.


								   static void

								   one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)

								   {

								     .. one minute over, w is actually stopped right here

								   }


								   ev_timer mytimer;

								   ev_timer_init (&mytimer, one_minute_cb, 60., 0.);

								   ev_timer_start (loop, &mytimer);


								Example: Create a timeout timer that times out after 10 seconds of

								inactivity.


								   static void

								   timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)

								   {

								     .. ten seconds without any activity

								   }


								   ev_timer mytimer;

								   ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */

								   ev_timer_again (&mytimer); /* start timer */

								   ev_run (loop, 0);


								   // and in some piece of code that gets executed on any "activity":

								   // reset the timeout to start ticking again at 10 seconds

								   ev_timer_again (&mytimer);


								=head2 C<ev_periodic> - to cron or not to cron?


								Periodic watchers are also timers of a kind, but they are very versatile

								(and unfortunately a bit complex).


								Unlike C<ev_timer>, periodic watchers are not based on real time (or

								relative time, the physical time that passes) but on wall clock time

								(absolute time, the thing you can read on your calender or clock). The

								difference is that wall clock time can run faster or slower than real

								time, and time jumps are not uncommon (e.g. when you adjust your

								wrist-watch).


								You can tell a periodic watcher to trigger after some specific point

								in time: for example, if you tell a periodic watcher to trigger "in 10

								seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time

								not a delay) and then reset your system clock to January of the previous

								year, then it will take a year or more to trigger the event (unlike an

								C<ev_timer>, which would still trigger roughly 10 seconds after starting

								it, as it uses a relative timeout).


								C<ev_periodic> watchers can also be used to implement vastly more complex

								timers, such as triggering an event on each "midnight, local time", or

								other complicated rules. This cannot be done with C<ev_timer> watchers, as

								those cannot react to time jumps.


								As with timers, the callback is guaranteed to be invoked only when the

								point in time where it is supposed to trigger has passed. If multiple

								timers become ready during the same loop iteration then the ones with

								earlier time-out values are invoked before ones with later time-out values

								(but this is no longer true when a callback calls C<ev_run> recursively).


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)


								=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)


								Lots of arguments, let's sort it out... There are basically three modes of

								operation, and we will explain them from simplest to most complex:


								=over 4


								=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)


								In this configuration the watcher triggers an event after the wall clock

								time C<offset> has passed. It will not repeat and will not adjust when a

								time jump occurs, that is, if it is to be run at January 1st 2011 then it

								will be stopped and invoked when the system clock reaches or surpasses

								this point in time.


								=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)


								In this mode the watcher will always be scheduled to time out at the next

								C<offset + N * interval> time (for some integer N, which can also be

								negative) and then repeat, regardless of any time jumps. The C<offset>

								argument is merely an offset into the C<interval> periods.


								This can be used to create timers that do not drift with respect to the

								system clock, for example, here is an C<ev_periodic> that triggers each

								hour, on the hour (with respect to UTC):


								   ev_periodic_set (&periodic, 0., 3600., 0);


								This doesn't mean there will always be 3600 seconds in between triggers,

								but only that the callback will be called when the system time shows a

								full hour (UTC), or more correctly, when the system time is evenly divisible

								by 3600.


								Another way to think about it (for the mathematically inclined) is that

								C<ev_periodic> will try to run the callback in this mode at the next possible

								time where C<time = offset (mod interval)>, regardless of any time jumps.


								For numerical stability it is preferable that the C<offset> value is near

								C<ev_now ()> (the current time), but there is no range requirement for

								this value, and in fact is often specified as zero.


								Note also that there is an upper limit to how often a timer can fire (CPU

								speed for example), so if C<interval> is very small then timing stability

								will of course deteriorate. Libev itself tries to be exact to be about one

								millisecond (if the OS supports it and the machine is fast enough).


								=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)


								In this mode the values for C<interval> and C<offset> are both being

								ignored. Instead, each time the periodic watcher gets scheduled, the

								reschedule callback will be called with the watcher as first, and the

								current time as second argument.


								NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,

								or make ANY other event loop modifications whatsoever, unless explicitly

								allowed by documentation here>.


								If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop

								it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the

								only event loop modification you are allowed to do).


								The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic

								*w, ev_tstamp now)>, e.g.:


								   static ev_tstamp

								   my_rescheduler (ev_periodic *w, ev_tstamp now)

								   {

								     return now + 60.;

								   }


								It must return the next time to trigger, based on the passed time value

								(that is, the lowest time value larger than to the second argument). It

								will usually be called just before the callback will be triggered, but

								might be called at other times, too.


								NOTE: I<< This callback must always return a time that is higher than or

								equal to the passed C<now> value >>.


								This can be used to create very complex timers, such as a timer that

								triggers on "next midnight, local time". To do this, you would calculate the

								next midnight after C<now> and return the timestamp value for this. How

								you do this is, again, up to you (but it is not trivial, which is the main

								reason I omitted it as an example).


								=back


								=item ev_periodic_again (loop, ev_periodic *)


								Simply stops and restarts the periodic watcher again. This is only useful

								when you changed some parameters or the reschedule callback would return

								a different time than the last time it was called (e.g. in a crond like

								program when the crontabs have changed).


								=item ev_tstamp ev_periodic_at (ev_periodic *)


								When active, returns the absolute time that the watcher is supposed

								to trigger next. This is not the same as the C<offset> argument to

								C<ev_periodic_set>, but indeed works even in interval and manual

								rescheduling modes.


								=item ev_tstamp offset [read-write]


								When repeating, this contains the offset value, otherwise this is the

								absolute point in time (the C<offset> value passed to C<ev_periodic_set>,

								although libev might modify this value for better numerical stability).


								Can be modified any time, but changes only take effect when the periodic

								timer fires or C<ev_periodic_again> is being called.


								=item ev_tstamp interval [read-write]


								The current interval value. Can be modified any time, but changes only

								take effect when the periodic timer fires or C<ev_periodic_again> is being

								called.


								=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]


								The current reschedule callback, or C<0>, if this functionality is

								switched off. Can be changed any time, but changes only take effect when

								the periodic timer fires or C<ev_periodic_again> is being called.


								=back


								=head3 Examples


								Example: Call a callback every hour, or, more precisely, whenever the

								system time is divisible by 3600. The callback invocation times have

								potentially a lot of jitter, but good long-term stability.


								   static void

								   clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)

								   {

								     ... its now a full hour (UTC, or TAI or whatever your clock follows)

								   }


								   ev_periodic hourly_tick;

								   ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);

								   ev_periodic_start (loop, &hourly_tick);


								Example: The same as above, but use a reschedule callback to do it:


								   #include <math.h>


								   static ev_tstamp

								   my_scheduler_cb (ev_periodic *w, ev_tstamp now)

								   {

								     return now + (3600. - fmod (now, 3600.));

								   }


								   ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);


								Example: Call a callback every hour, starting now:


								   ev_periodic hourly_tick;

								   ev_periodic_init (&hourly_tick, clock_cb,

								                     fmod (ev_now (loop), 3600.), 3600., 0);

								   ev_periodic_start (loop, &hourly_tick);


								=head2 C<ev_signal> - signal me when a signal gets signalled!


								Signal watchers will trigger an event when the process receives a specific

								signal one or more times. Even though signals are very asynchronous, libev

								will try its best to deliver signals synchronously, i.e. as part of the

								normal event processing, like any other event.


								If you want signals to be delivered truly asynchronously, just use

								C<sigaction> as you would do without libev and forget about sharing

								the signal. You can even use C<ev_async> from a signal handler to

								synchronously wake up an event loop.


								You can configure as many watchers as you like for the same signal, but

								only within the same loop, i.e. you can watch for C<SIGINT> in your

								default loop and for C<SIGIO> in another loop, but you cannot watch for

								C<SIGINT> in both the default loop and another loop at the same time. At

								the moment, C<SIGCHLD> is permanently tied to the default loop.


								When the first watcher gets started will libev actually register something

								with the kernel (thus it coexists with your own signal handlers as long as

								you don't register any with libev for the same signal).


								If possible and supported, libev will install its handlers with

								C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should

								not be unduly interrupted. If you have a problem with system calls getting

								interrupted by signals you can block all signals in an C<ev_check> watcher

								and unblock them in an C<ev_prepare> watcher.


								=head3 The special problem of inheritance over fork/execve/pthread_create


								Both the signal mask (C<sigprocmask>) and the signal disposition

								(C<sigaction>) are unspecified after starting a signal watcher (and after

								stopping it again), that is, libev might or might not block the signal,

								and might or might not set or restore the installed signal handler (but

								see C<EVFLAG_NOSIGMASK>).


								While this does not matter for the signal disposition (libev never

								sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on

								C<execve>), this matters for the signal mask: many programs do not expect

								certain signals to be blocked.


								This means that before calling C<exec> (from the child) you should reset

								the signal mask to whatever "default" you expect (all clear is a good

								choice usually).


								The simplest way to ensure that the signal mask is reset in the child is

								to install a fork handler with C<pthread_atfork> that resets it. That will

								catch fork calls done by libraries (such as the libc) as well.


								In current versions of libev, the signal will not be blocked indefinitely

								unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces

								the window of opportunity for problems, it will not go away, as libev

								I<has> to modify the signal mask, at least temporarily.


								So I can't stress this enough: I<If you do not reset your signal mask when

								you expect it to be empty, you have a race condition in your code>. This

								is not a libev-specific thing, this is true for most event libraries.


								=head3 The special problem of threads signal handling


								POSIX threads has problematic signal handling semantics, specifically,

								a lot of functionality (sigfd, sigwait etc.) only really works if all

								threads in a process block signals, which is hard to achieve.


								When you want to use sigwait (or mix libev signal handling with your own

								for the same signals), you can tackle this problem by globally blocking

								all signals before creating any threads (or creating them with a fully set

								sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating

								loops. Then designate one thread as "signal receiver thread" which handles

								these signals. You can pass on any signals that libev might be interested

								in by calling C<ev_feed_signal>.


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_signal_init (ev_signal *, callback, int signum)


								=item ev_signal_set (ev_signal *, int signum)


								Configures the watcher to trigger on the given signal number (usually one

								of the C<SIGxxx> constants).


								=item int signum [read-only]


								The signal the watcher watches out for.


								=back


								=head3 Examples


								Example: Try to exit cleanly on SIGINT.


								   static void

								   sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)

								   {

								     ev_break (loop, EVBREAK_ALL);

								   }


								   ev_signal signal_watcher;

								   ev_signal_init (&signal_watcher, sigint_cb, SIGINT);

								   ev_signal_start (loop, &signal_watcher);


								=head2 C<ev_child> - watch out for process status changes


								Child watchers trigger when your process receives a SIGCHLD in response to

								some child status changes (most typically when a child of yours dies or

								exits). It is permissible to install a child watcher I<after> the child

								has been forked (which implies it might have already exited), as long

								as the event loop isn't entered (or is continued from a watcher), i.e.,

								forking and then immediately registering a watcher for the child is fine,

								but forking and registering a watcher a few event loop iterations later or

								in the next callback invocation is not.


								Only the default event loop is capable of handling signals, and therefore

								you can only register child watchers in the default event loop.


								Due to some design glitches inside libev, child watchers will always be

								handled at maximum priority (their priority is set to C<EV_MAXPRI> by

								libev)


								=head3 Process Interaction


								Libev grabs C<SIGCHLD> as soon as the default event loop is

								initialised. This is necessary to guarantee proper behaviour even if the

								first child watcher is started after the child exits. The occurrence

								of C<SIGCHLD> is recorded asynchronously, but child reaping is done

								synchronously as part of the event loop processing. Libev always reaps all

								children, even ones not watched.


								=head3 Overriding the Built-In Processing


								Libev offers no special support for overriding the built-in child

								processing, but if your application collides with libev's default child

								handler, you can override it easily by installing your own handler for

								C<SIGCHLD> after initialising the default loop, and making sure the

								default loop never gets destroyed. You are encouraged, however, to use an

								event-based approach to child reaping and thus use libev's support for

								that, so other libev users can use C<ev_child> watchers freely.


								=head3 Stopping the Child Watcher


								Currently, the child watcher never gets stopped, even when the

								child terminates, so normally one needs to stop the watcher in the

								callback. Future versions of libev might stop the watcher automatically

								when a child exit is detected (calling C<ev_child_stop> twice is not a

								problem).


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_child_init (ev_child *, callback, int pid, int trace)


								=item ev_child_set (ev_child *, int pid, int trace)


								Configures the watcher to wait for status changes of process C<pid> (or

								I<any> process if C<pid> is specified as C<0>). The callback can look

								at the C<rstatus> member of the C<ev_child> watcher structure to see

								the status word (use the macros from C<sys/wait.h> and see your systems

								C<waitpid> documentation). The C<rpid> member contains the pid of the

								process causing the status change. C<trace> must be either C<0> (only

								activate the watcher when the process terminates) or C<1> (additionally

								activate the watcher when the process is stopped or continued).


								=item int pid [read-only]


								The process id this watcher watches out for, or C<0>, meaning any process id.


								=item int rpid [read-write]


								The process id that detected a status change.


								=item int rstatus [read-write]


								The process exit/trace status caused by C<rpid> (see your systems

								C<waitpid> and C<sys/wait.h> documentation for details).


								=back


								=head3 Examples


								Example: C<fork()> a new process and install a child handler to wait for

								its completion.


								   ev_child cw;


								   static void

								   child_cb (EV_P_ ev_child *w, int revents)

								   {

								     ev_child_stop (EV_A_ w);

								     printf ("process %d exited with status %x\n", w->rpid, w->rstatus);

								   }


								   pid_t pid = fork ();


								   if (pid < 0)

								     // error

								   else if (pid == 0)

								     {

								       // the forked child executes here

								       exit (1);

								     }

								   else

								     {

								       ev_child_init (&cw, child_cb, pid, 0);

								       ev_child_start (EV_DEFAULT_ &cw);

								     }


								=head2 C<ev_stat> - did the file attributes just change?


								This watches a file system path for attribute changes. That is, it calls

								C<stat> on that path in regular intervals (or when the OS says it changed)

								and sees if it changed compared to the last time, invoking the callback if

								it did.


								The path does not need to exist: changing from "path exists" to "path does

								not exist" is a status change like any other. The condition "path does not

								exist" (or more correctly "path cannot be stat'ed") is signified by the

								C<st_nlink> field being zero (which is otherwise always forced to be at

								least one) and all the other fields of the stat buffer having unspecified

								contents.


								The path I<must not> end in a slash or contain special components such as

								C<.> or C<..>. The path I<should> be absolute: If it is relative and

								your working directory changes, then the behaviour is undefined.


								Since there is no portable change notification interface available, the

								portable implementation simply calls C<stat(2)> regularly on the path

								to see if it changed somehow. You can specify a recommended polling

								interval for this case. If you specify a polling interval of C<0> (highly

								recommended!) then a I<suitable, unspecified default> value will be used

								(which you can expect to be around five seconds, although this might

								change dynamically). Libev will also impose a minimum interval which is

								currently around C<0.1>, but that's usually overkill.


								This watcher type is not meant for massive numbers of stat watchers,

								as even with OS-supported change notifications, this can be

								resource-intensive.


								At the time of this writing, the only OS-specific interface implemented

								is the Linux inotify interface (implementing kqueue support is left as an

								exercise for the reader. Note, however, that the author sees no way of

								implementing C<ev_stat> semantics with kqueue, except as a hint).


								=head3 ABI Issues (Largefile Support)


								Libev by default (unless the user overrides this) uses the default

								compilation environment, which means that on systems with large file

								support disabled by default, you get the 32 bit version of the stat

								structure. When using the library from programs that change the ABI to

								use 64 bit file offsets the programs will fail. In that case you have to

								compile libev with the same flags to get binary compatibility. This is

								obviously the case with any flags that change the ABI, but the problem is

								most noticeably displayed with ev_stat and large file support.


								The solution for this is to lobby your distribution maker to make large

								file interfaces available by default (as e.g. FreeBSD does) and not

								optional. Libev cannot simply switch on large file support because it has

								to exchange stat structures with application programs compiled using the

								default compilation environment.


								=head3 Inotify and Kqueue


								When C<inotify (7)> support has been compiled into libev and present at

								runtime, it will be used to speed up change detection where possible. The

								inotify descriptor will be created lazily when the first C<ev_stat>

								watcher is being started.


								Inotify presence does not change the semantics of C<ev_stat> watchers

								except that changes might be detected earlier, and in some cases, to avoid

								making regular C<stat> calls. Even in the presence of inotify support

								there are many cases where libev has to resort to regular C<stat> polling,

								but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too

								many bugs), the path exists (i.e. stat succeeds), and the path resides on

								a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and

								xfs are fully working) libev usually gets away without polling.


								There is no support for kqueue, as apparently it cannot be used to

								implement this functionality, due to the requirement of having a file

								descriptor open on the object at all times, and detecting renames, unlinks

								etc. is difficult.


								=head3 C<stat ()> is a synchronous operation


								Libev doesn't normally do any kind of I/O itself, and so is not blocking

								the process. The exception are C<ev_stat> watchers - those call C<stat

								()>, which is a synchronous operation.


								For local paths, this usually doesn't matter: unless the system is very

								busy or the intervals between stat's are large, a stat call will be fast,

								as the path data is usually in memory already (except when starting the

								watcher).


								For networked file systems, calling C<stat ()> can block an indefinite

								time due to network issues, and even under good conditions, a stat call

								often takes multiple milliseconds.


								Therefore, it is best to avoid using C<ev_stat> watchers on networked

								paths, although this is fully supported by libev.


								=head3 The special problem of stat time resolution


								The C<stat ()> system call only supports full-second resolution portably,

								and even on systems where the resolution is higher, most file systems

								still only support whole seconds.


								That means that, if the time is the only thing that changes, you can

								easily miss updates: on the first update, C<ev_stat> detects a change and

								calls your callback, which does something. When there is another update

								within the same second, C<ev_stat> will be unable to detect unless the

								stat data does change in other ways (e.g. file size).


								The solution to this is to delay acting on a change for slightly more

								than a second (or till slightly after the next full second boundary), using

								a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);

								ev_timer_again (loop, w)>).


								The C<.02> offset is added to work around small timing inconsistencies

								of some operating systems (where the second counter of the current time

								might be be delayed. One such system is the Linux kernel, where a call to

								C<gettimeofday> might return a timestamp with a full second later than

								a subsequent C<time> call - if the equivalent of C<time ()> is used to

								update file times then there will be a small window where the kernel uses

								the previous second to update file times but libev might already execute

								the timer callback).


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)


								=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)


								Configures the watcher to wait for status changes of the given

								C<path>. The C<interval> is a hint on how quickly a change is expected to

								be detected and should normally be specified as C<0> to let libev choose

								a suitable value. The memory pointed to by C<path> must point to the same

								path for as long as the watcher is active.


								The callback will receive an C<EV_STAT> event when a change was detected,

								relative to the attributes at the time the watcher was started (or the

								last change was detected).


								=item ev_stat_stat (loop, ev_stat *)


								Updates the stat buffer immediately with new values. If you change the

								watched path in your callback, you could call this function to avoid

								detecting this change (while introducing a race condition if you are not

								the only one changing the path). Can also be useful simply to find out the

								new values.


								=item ev_statdata attr [read-only]


								The most-recently detected attributes of the file. Although the type is

								C<ev_statdata>, this is usually the (or one of the) C<struct stat> types

								suitable for your system, but you can only rely on the POSIX-standardised

								members to be present. If the C<st_nlink> member is C<0>, then there was

								some error while C<stat>ing the file.


								=item ev_statdata prev [read-only]


								The previous attributes of the file. The callback gets invoked whenever

								C<prev> != C<attr>, or, more precisely, one or more of these members

								differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,

								C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.


								=item ev_tstamp interval [read-only]


								The specified interval.


								=item const char *path [read-only]


								The file system path that is being watched.


								=back


								=head3 Examples


								Example: Watch C</etc/passwd> for attribute changes.


								   static void

								   passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)

								   {

								     /* /etc/passwd changed in some way */

								     if (w->attr.st_nlink)

								       {

								         printf ("passwd current size  %ld\n", (long)w->attr.st_size);

								         printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);

								         printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);

								       }

								     else

								       /* you shalt not abuse printf for puts */

								       puts ("wow, /etc/passwd is not there, expect problems. "

								             "if this is windows, they already arrived\n");

								   }


								   ...

								   ev_stat passwd;


								   ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);

								   ev_stat_start (loop, &passwd);


								Example: Like above, but additionally use a one-second delay so we do not

								miss updates (however, frequent updates will delay processing, too, so

								one might do the work both on C<ev_stat> callback invocation I<and> on

								C<ev_timer> callback invocation).


								   static ev_stat passwd;

								   static ev_timer timer;


								   static void

								   timer_cb (EV_P_ ev_timer *w, int revents)

								   {

								     ev_timer_stop (EV_A_ w);


								     /* now it's one second after the most recent passwd change */

								   }


								   static void

								   stat_cb (EV_P_ ev_stat *w, int revents)

								   {

								     /* reset the one-second timer */

								     ev_timer_again (EV_A_ &timer);

								   }


								   ...

								   ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);

								   ev_stat_start (loop, &passwd);

								   ev_timer_init (&timer, timer_cb, 0., 1.02);


								=head2 C<ev_idle> - when you've got nothing better to do...


								Idle watchers trigger events when no other events of the same or higher

								priority are pending (prepare, check and other idle watchers do not count

								as receiving "events").


								That is, as long as your process is busy handling sockets or timeouts

								(or even signals, imagine) of the same or higher priority it will not be

								triggered. But when your process is idle (or only lower-priority watchers

								are pending), the idle watchers are being called once per event loop

								iteration - until stopped, that is, or your process receives more events

								and becomes busy again with higher priority stuff.


								The most noteworthy effect is that as long as any idle watchers are

								active, the process will not block when waiting for new events.


								Apart from keeping your process non-blocking (which is a useful

								effect on its own sometimes), idle watchers are a good place to do

								"pseudo-background processing", or delay processing stuff to after the

								event loop has handled all outstanding events.


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_idle_init (ev_idle *, callback)


								Initialises and configures the idle watcher - it has no parameters of any

								kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,

								believe me.


								=back


								=head3 Examples


								Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the

								callback, free it. Also, use no error checking, as usual.


								   static void

								   idle_cb (struct ev_loop *loop, ev_idle *w, int revents)

								   {

								     free (w);

								     // now do something you wanted to do when the program has

								     // no longer anything immediate to do.

								   }


								   ev_idle *idle_watcher = malloc (sizeof (ev_idle));

								   ev_idle_init (idle_watcher, idle_cb);

								   ev_idle_start (loop, idle_watcher);


								=head2 C<ev_prepare> and C<ev_check> - customise your event loop!


								Prepare and check watchers are usually (but not always) used in pairs:

								prepare watchers get invoked before the process blocks and check watchers

								afterwards.


								You I<must not> call C<ev_run> or similar functions that enter

								the current event loop from either C<ev_prepare> or C<ev_check>

								watchers. Other loops than the current one are fine, however. The

								rationale behind this is that you do not need to check for recursion in

								those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,

								C<ev_check> so if you have one watcher of each kind they will always be

								called in pairs bracketing the blocking call.


								Their main purpose is to integrate other event mechanisms into libev and

								their use is somewhat advanced. They could be used, for example, to track

								variable changes, implement your own watchers, integrate net-snmp or a

								coroutine library and lots more. They are also occasionally useful if

								you cache some data and want to flush it before blocking (for example,

								in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>

								watcher).


								This is done by examining in each prepare call which file descriptors

								need to be watched by the other library, registering C<ev_io> watchers

								for them and starting an C<ev_timer> watcher for any timeouts (many

								libraries provide exactly this functionality). Then, in the check watcher,

								you check for any events that occurred (by checking the pending status

								of all watchers and stopping them) and call back into the library. The

								I/O and timer callbacks will never actually be called (but must be valid

								nevertheless, because you never know, you know?).


								As another example, the Perl Coro module uses these hooks to integrate

								coroutines into libev programs, by yielding to other active coroutines

								during each prepare and only letting the process block if no coroutines

								are ready to run (it's actually more complicated: it only runs coroutines

								with priority higher than or equal to the event loop and one coroutine

								of lower priority, but only once, using idle watchers to keep the event

								loop from blocking if lower-priority coroutines are active, thus mapping

								low-priority coroutines to idle/background tasks).


								It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)

								priority, to ensure that they are being run before any other watchers

								after the poll (this doesn't matter for C<ev_prepare> watchers).


								Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not

								activate ("feed") events into libev. While libev fully supports this, they

								might get executed before other C<ev_check> watchers did their job. As

								C<ev_check> watchers are often used to embed other (non-libev) event

								loops those other event loops might be in an unusable state until their

								C<ev_check> watcher ran (always remind yourself to coexist peacefully with

								others).


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_prepare_init (ev_prepare *, callback)


								=item ev_check_init (ev_check *, callback)


								Initialises and configures the prepare or check watcher - they have no

								parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>

								macros, but using them is utterly, utterly, utterly and completely

								pointless.


								=back


								=head3 Examples


								There are a number of principal ways to embed other event loops or modules

								into libev. Here are some ideas on how to include libadns into libev

								(there is a Perl module named C<EV::ADNS> that does this, which you could

								use as a working example. Another Perl module named C<EV::Glib> embeds a

								Glib main context into libev, and finally, C<Glib::EV> embeds EV into the

								Glib event loop).


								Method 1: Add IO watchers and a timeout watcher in a prepare handler,

								and in a check watcher, destroy them and call into libadns. What follows

								is pseudo-code only of course. This requires you to either use a low

								priority for the check watcher or use C<ev_clear_pending> explicitly, as

								the callbacks for the IO/timeout watchers might not have been called yet.


								   static ev_io iow [nfd];

								   static ev_timer tw;


								   static void

								   io_cb (struct ev_loop *loop, ev_io *w, int revents)

								   {

								   }


								   // create io watchers for each fd and a timer before blocking

								   static void

								   adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)

								   {

								     int timeout = 3600000;

								     struct pollfd fds [nfd];

								     // actual code will need to loop here and realloc etc.

								     adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));


								     /* the callback is illegal, but won't be called as we stop during check */

								     ev_timer_init (&tw, 0, timeout * 1e-3, 0.);

								     ev_timer_start (loop, &tw);


								     // create one ev_io per pollfd

								     for (int i = 0; i < nfd; ++i)

								       {

								         ev_io_init (iow + i, io_cb, fds [i].fd,

								           ((fds [i].events & POLLIN ? EV_READ : 0)

								            | (fds [i].events & POLLOUT ? EV_WRITE : 0)));


								         fds [i].revents = 0;

								         ev_io_start (loop, iow + i);

								       }

								   }


								   // stop all watchers after blocking

								   static void

								   adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)

								   {

								     ev_timer_stop (loop, &tw);


								     for (int i = 0; i < nfd; ++i)

								       {

								         // set the relevant poll flags

								         // could also call adns_processreadable etc. here

								         struct pollfd *fd = fds + i;

								         int revents = ev_clear_pending (iow + i);

								         if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;

								         if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;


								         // now stop the watcher

								         ev_io_stop (loop, iow + i);

								       }


								     adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));

								   }


								Method 2: This would be just like method 1, but you run C<adns_afterpoll>

								in the prepare watcher and would dispose of the check watcher.


								Method 3: If the module to be embedded supports explicit event

								notification (libadns does), you can also make use of the actual watcher

								callbacks, and only destroy/create the watchers in the prepare watcher.


								   static void

								   timer_cb (EV_P_ ev_timer *w, int revents)

								   {

								     adns_state ads = (adns_state)w->data;

								     update_now (EV_A);


								     adns_processtimeouts (ads, &tv_now);

								   }


								   static void

								   io_cb (EV_P_ ev_io *w, int revents)

								   {

								     adns_state ads = (adns_state)w->data;

								     update_now (EV_A);


								     if (revents & EV_READ ) adns_processreadable  (ads, w->fd, &tv_now);

								     if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);

								   }


								   // do not ever call adns_afterpoll


								Method 4: Do not use a prepare or check watcher because the module you

								want to embed is not flexible enough to support it. Instead, you can

								override their poll function. The drawback with this solution is that the

								main loop is now no longer controllable by EV. The C<Glib::EV> module uses

								this approach, effectively embedding EV as a client into the horrible

								libglib event loop.


								   static gint

								   event_poll_func (GPollFD *fds, guint nfds, gint timeout)

								   {

								     int got_events = 0;


								     for (n = 0; n < nfds; ++n)

								       // create/start io watcher that sets the relevant bits in fds[n] and increment got_events


								     if (timeout >= 0)

								       // create/start timer


								     // poll

								     ev_run (EV_A_ 0);


								     // stop timer again

								     if (timeout >= 0)

								       ev_timer_stop (EV_A_ &to);


								     // stop io watchers again - their callbacks should have set

								     for (n = 0; n < nfds; ++n)

								       ev_io_stop (EV_A_ iow [n]);


								     return got_events;

								   }


								=head2 C<ev_embed> - when one backend isn't enough...


								This is a rather advanced watcher type that lets you embed one event loop

								into another (currently only C<ev_io> events are supported in the embedded

								loop, other types of watchers might be handled in a delayed or incorrect

								fashion and must not be used).


								There are primarily two reasons you would want that: work around bugs and

								prioritise I/O.


								As an example for a bug workaround, the kqueue backend might only support

								sockets on some platform, so it is unusable as generic backend, but you

								still want to make use of it because you have many sockets and it scales

								so nicely. In this case, you would create a kqueue-based loop and embed

								it into your default loop (which might use e.g. poll). Overall operation

								will be a bit slower because first libev has to call C<poll> and then

								C<kevent>, but at least you can use both mechanisms for what they are

								best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)


								As for prioritising I/O: under rare circumstances you have the case where

								some fds have to be watched and handled very quickly (with low latency),

								and even priorities and idle watchers might have too much overhead. In

								this case you would put all the high priority stuff in one loop and all

								the rest in a second one, and embed the second one in the first.


								As long as the watcher is active, the callback will be invoked every

								time there might be events pending in the embedded loop. The callback

								must then call C<ev_embed_sweep (mainloop, watcher)> to make a single

								sweep and invoke their callbacks (the callback doesn't need to invoke the

								C<ev_embed_sweep> function directly, it could also start an idle watcher

								to give the embedded loop strictly lower priority for example).


								You can also set the callback to C<0>, in which case the embed watcher

								will automatically execute the embedded loop sweep whenever necessary.


								Fork detection will be handled transparently while the C<ev_embed> watcher

								is active, i.e., the embedded loop will automatically be forked when the

								embedding loop forks. In other cases, the user is responsible for calling

								C<ev_loop_fork> on the embedded loop.


								Unfortunately, not all backends are embeddable: only the ones returned by

								C<ev_embeddable_backends> are, which, unfortunately, does not include any

								portable one.


								So when you want to use this feature you will always have to be prepared

								that you cannot get an embeddable loop. The recommended way to get around

								this is to have a separate variables for your embeddable loop, try to

								create it, and if that fails, use the normal loop for everything.


								=head3 C<ev_embed> and fork


								While the C<ev_embed> watcher is running, forks in the embedding loop will

								automatically be applied to the embedded loop as well, so no special

								fork handling is required in that case. When the watcher is not running,

								however, it is still the task of the libev user to call C<ev_loop_fork ()>

								as applicable.


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)


								=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)


								Configures the watcher to embed the given loop, which must be

								embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be

								invoked automatically, otherwise it is the responsibility of the callback

								to invoke it (it will continue to be called until the sweep has been done,

								if you do not want that, you need to temporarily stop the embed watcher).


								=item ev_embed_sweep (loop, ev_embed *)


								Make a single, non-blocking sweep over the embedded loop. This works

								similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most

								appropriate way for embedded loops.


								=item struct ev_loop *other [read-only]


								The embedded event loop.


								=back


								=head3 Examples


								Example: Try to get an embeddable event loop and embed it into the default

								event loop. If that is not possible, use the default loop. The default

								loop is stored in C<loop_hi>, while the embeddable loop is stored in

								C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be

								used).


								   struct ev_loop *loop_hi = ev_default_init (0);

								   struct ev_loop *loop_lo = 0;

								   ev_embed embed;


								   // see if there is a chance of getting one that works

								   // (remember that a flags value of 0 means autodetection)

								   loop_lo = ev_embeddable_backends () & ev_recommended_backends ()

								     ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())

								     : 0;


								   // if we got one, then embed it, otherwise default to loop_hi

								   if (loop_lo)

								     {

								       ev_embed_init (&embed, 0, loop_lo);

								       ev_embed_start (loop_hi, &embed);

								     }

								   else

								     loop_lo = loop_hi;


								Example: Check if kqueue is available but not recommended and create

								a kqueue backend for use with sockets (which usually work with any

								kqueue implementation). Store the kqueue/socket-only event loop in

								C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).


								   struct ev_loop *loop = ev_default_init (0);

								   struct ev_loop *loop_socket = 0;

								   ev_embed embed;


								   if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)

								     if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))

								       {

								         ev_embed_init (&embed, 0, loop_socket);

								         ev_embed_start (loop, &embed);

								       }


								   if (!loop_socket)

								     loop_socket = loop;


								   // now use loop_socket for all sockets, and loop for everything else


								=head2 C<ev_fork> - the audacity to resume the event loop after a fork


								Fork watchers are called when a C<fork ()> was detected (usually because

								whoever is a good citizen cared to tell libev about it by calling

								C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the

								event loop blocks next and before C<ev_check> watchers are being called,

								and only in the child after the fork. If whoever good citizen calling

								C<ev_default_fork> cheats and calls it in the wrong process, the fork

								handlers will be invoked, too, of course.


								=head3 The special problem of life after fork - how is it possible?


								Most uses of C<fork()> consist of forking, then some simple calls to set

								up/change the process environment, followed by a call to C<exec()>. This

								sequence should be handled by libev without any problems.


								This changes when the application actually wants to do event handling

								in the child, or both parent in child, in effect "continuing" after the

								fork.


								The default mode of operation (for libev, with application help to detect

								forks) is to duplicate all the state in the child, as would be expected

								when I<either> the parent I<or> the child process continues.


								When both processes want to continue using libev, then this is usually the

								wrong result. In that case, usually one process (typically the parent) is

								supposed to continue with all watchers in place as before, while the other

								process typically wants to start fresh, i.e. without any active watchers.


								The cleanest and most efficient way to achieve that with libev is to

								simply create a new event loop, which of course will be "empty", and

								use that for new watchers. This has the advantage of not touching more

								memory than necessary, and thus avoiding the copy-on-write, and the

								disadvantage of having to use multiple event loops (which do not support

								signal watchers).


								When this is not possible, or you want to use the default loop for

								other reasons, then in the process that wants to start "fresh", call

								C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.

								Destroying the default loop will "orphan" (not stop) all registered

								watchers, so you have to be careful not to execute code that modifies

								those watchers. Note also that in that case, you have to re-register any

								signal watchers.


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_fork_init (ev_fork *, callback)


								Initialises and configures the fork watcher - it has no parameters of any

								kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,

								really.


								=back


								=head2 C<ev_cleanup> - even the best things end


								Cleanup watchers are called just before the event loop is being destroyed

								by a call to C<ev_loop_destroy>.


								While there is no guarantee that the event loop gets destroyed, cleanup

								watchers provide a convenient method to install cleanup hooks for your

								program, worker threads and so on - you just to make sure to destroy the

								loop when you want them to be invoked.


								Cleanup watchers are invoked in the same way as any other watcher. Unlike

								all other watchers, they do not keep a reference to the event loop (which

								makes a lot of sense if you think about it). Like all other watchers, you

								can call libev functions in the callback, except C<ev_cleanup_start>.


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_cleanup_init (ev_cleanup *, callback)


								Initialises and configures the cleanup watcher - it has no parameters of

								any kind. There is a C<ev_cleanup_set> macro, but using it is utterly

								pointless, I assure you.


								=back


								Example: Register an atexit handler to destroy the default loop, so any

								cleanup functions are called.


								   static void

								   program_exits (void)

								   {

								     ev_loop_destroy (EV_DEFAULT_UC);

								   }


								   ...

								   atexit (program_exits);


								=head2 C<ev_async> - how to wake up an event loop


								In general, you cannot use an C<ev_loop> from multiple threads or other

								asynchronous sources such as signal handlers (as opposed to multiple event

								loops - those are of course safe to use in different threads).


								Sometimes, however, you need to wake up an event loop you do not control,

								for example because it belongs to another thread. This is what C<ev_async>

								watchers do: as long as the C<ev_async> watcher is active, you can signal

								it by calling C<ev_async_send>, which is thread- and signal safe.


								This functionality is very similar to C<ev_signal> watchers, as signals,

								too, are asynchronous in nature, and signals, too, will be compressed

								(i.e. the number of callback invocations may be less than the number of

								C<ev_async_sent> calls). In fact, you could use signal watchers as a kind

								of "global async watchers" by using a watcher on an otherwise unused

								signal, and C<ev_feed_signal> to signal this watcher from another thread,

								even without knowing which loop owns the signal.


								Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not

								just the default loop.


								=head3 Queueing


								C<ev_async> does not support queueing of data in any way. The reason

								is that the author does not know of a simple (or any) algorithm for a

								multiple-writer-single-reader queue that works in all cases and doesn't

								need elaborate support such as pthreads or unportable memory access

								semantics.


								That means that if you want to queue data, you have to provide your own

								queue. But at least I can tell you how to implement locking around your

								queue:


								=over 4


								=item queueing from a signal handler context


								To implement race-free queueing, you simply add to the queue in the signal

								handler but you block the signal handler in the watcher callback. Here is

								an example that does that for some fictitious SIGUSR1 handler:


								   static ev_async mysig;


								   static void

								   sigusr1_handler (void)

								   {

								     sometype data;


								     // no locking etc.

								     queue_put (data);

								     ev_async_send (EV_DEFAULT_ &mysig);

								   }


								   static void

								   mysig_cb (EV_P_ ev_async *w, int revents)

								   {

								     sometype data;

								     sigset_t block, prev;


								     sigemptyset (&block);

								     sigaddset (&block, SIGUSR1);

								     sigprocmask (SIG_BLOCK, &block, &prev);


								     while (queue_get (&data))

								       process (data);


								     if (sigismember (&prev, SIGUSR1)

								       sigprocmask (SIG_UNBLOCK, &block, 0);

								   }


								(Note: pthreads in theory requires you to use C<pthread_setmask>

								instead of C<sigprocmask> when you use threads, but libev doesn't do it

								either...).


								=item queueing from a thread context


								The strategy for threads is different, as you cannot (easily) block

								threads but you can easily preempt them, so to queue safely you need to

								employ a traditional mutex lock, such as in this pthread example:


								   static ev_async mysig;

								   static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;


								   static void

								   otherthread (void)

								   {

								     // only need to lock the actual queueing operation

								     pthread_mutex_lock (&mymutex);

								     queue_put (data);

								     pthread_mutex_unlock (&mymutex);


								     ev_async_send (EV_DEFAULT_ &mysig);

								   }


								   static void

								   mysig_cb (EV_P_ ev_async *w, int revents)

								   {

								     pthread_mutex_lock (&mymutex);


								     while (queue_get (&data))

								       process (data);


								     pthread_mutex_unlock (&mymutex);

								   }


								=back


								=head3 Watcher-Specific Functions and Data Members


								=over 4


								=item ev_async_init (ev_async *, callback)


								Initialises and configures the async watcher - it has no parameters of any

								kind. There is a C<ev_async_set> macro, but using it is utterly pointless,

								trust me.


								=item ev_async_send (loop, ev_async *)


								Sends/signals/activates the given C<ev_async> watcher, that is, feeds

								an C<EV_ASYNC> event on the watcher into the event loop, and instantly

								returns.


								Unlike C<ev_feed_event>, this call is safe to do from other threads,

								signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the

								embedding section below on what exactly this means).


								Note that, as with other watchers in libev, multiple events might get

								compressed into a single callback invocation (another way to look at this

								is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,

								reset when the event loop detects that).


								This call incurs the overhead of a system call only once per event loop

								iteration, so while the overhead might be noticeable, it doesn't apply to

								repeated calls to C<ev_async_send> for the same event loop.


								=item bool = ev_async_pending (ev_async *)


								Returns a non-zero value when C<ev_async_send> has been called on the

								watcher but the event has not yet been processed (or even noted) by the

								event loop.


								C<ev_async_send> sets a flag in the watcher and wakes up the loop. When

								the loop iterates next and checks for the watcher to have become active,

								it will reset the flag again. C<ev_async_pending> can be used to very

								quickly check whether invoking the loop might be a good idea.


								Not that this does I<not> check whether the watcher itself is pending,

								only whether it has been requested to make this watcher pending: there

								is a time window between the event loop checking and resetting the async

								notification, and the callback being invoked.


								=back


								=head1 OTHER FUNCTIONS


								There are some other functions of possible interest. Described. Here. Now.


								=over 4


								=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)


								This function combines a simple timer and an I/O watcher, calls your

								callback on whichever event happens first and automatically stops both

								watchers. This is useful if you want to wait for a single event on an fd

								or timeout without having to allocate/configure/start/stop/free one or

								more watchers yourself.


								If C<fd> is less than 0, then no I/O watcher will be started and the

								C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for

								the given C<fd> and C<events> set will be created and started.


								If C<timeout> is less than 0, then no timeout watcher will be

								started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and

								repeat = 0) will be started. C<0> is a valid timeout.


								The callback has the type C<void (*cb)(int revents, void *arg)> and is

								passed an C<revents> set like normal event callbacks (a combination of

								C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>

								value passed to C<ev_once>. Note that it is possible to receive I<both>

								a timeout and an io event at the same time - you probably should give io

								events precedence.


								Example: wait up to ten seconds for data to appear on STDIN_FILENO.


								   static void stdin_ready (int revents, void *arg)

								   {

								     if (revents & EV_READ)

								       /* stdin might have data for us, joy! */;

								     else if (revents & EV_TIMER)

								       /* doh, nothing entered */;

								   }


								   ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);


								=item ev_feed_fd_event (loop, int fd, int revents)


								Feed an event on the given fd, as if a file descriptor backend detected

								the given events it.


								=item ev_feed_signal_event (loop, int signum)


								Feed an event as if the given signal occurred. See also C<ev_feed_signal>,

								which is async-safe.


								=back


								=head1 COMMON OR USEFUL IDIOMS (OR BOTH)


								This section explains some common idioms that are not immediately

								obvious. Note that examples are sprinkled over the whole manual, and this

								section only contains stuff that wouldn't fit anywhere else.


								=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER


								Each watcher has, by default, a C<void *data> member that you can read

								or modify at any time: libev will completely ignore it. This can be used

								to associate arbitrary data with your watcher. If you need more data and

								don't want to allocate memory separately and store a pointer to it in that

								data member, you can also "subclass" the watcher type and provide your own

								data:


								   struct my_io

								   {

								     ev_io io;

								     int otherfd;

								     void *somedata;

								     struct whatever *mostinteresting;

								   };


								   ...

								   struct my_io w;

								   ev_io_init (&w.io, my_cb, fd, EV_READ);


								And since your callback will be called with a pointer to the watcher, you

								can cast it back to your own type:


								   static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)

								   {

								     struct my_io *w = (struct my_io *)w_;

								     ...

								   }


								More interesting and less C-conformant ways of casting your callback

								function type instead have been omitted.


								=head2 BUILDING YOUR OWN COMPOSITE WATCHERS


								Another common scenario is to use some data structure with multiple

								embedded watchers, in effect creating your own watcher that combines

								multiple libev event sources into one "super-watcher":


								   struct my_biggy

								   {

								     int some_data;

								     ev_timer t1;

								     ev_timer t2;

								   }


								In this case getting the pointer to C<my_biggy> is a bit more

								complicated: Either you store the address of your C<my_biggy> struct in

								the C<data> member of the watcher (for woozies or C++ coders), or you need

								to use some pointer arithmetic using C<offsetof> inside your watchers (for

								real programmers):


								   #include <stddef.h>


								   static void

								   t1_cb (EV_P_ ev_timer *w, int revents)

								   {

								     struct my_biggy big = (struct my_biggy *)

								       (((char *)w) - offsetof (struct my_biggy, t1));

								   }


								   static void

								   t2_cb (EV_P_ ev_timer *w, int revents)

								   {

								     struct my_biggy big = (struct my_biggy *)

								       (((char *)w) - offsetof (struct my_biggy, t2));

								   }


								=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS


								Often (especially in GUI toolkits) there are places where you have

								I<modal> interaction, which is most easily implemented by recursively

								invoking C<ev_run>.


								This brings the problem of exiting - a callback might want to finish the

								main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but

								a modal "Are you sure?" dialog is still waiting), or just the nested one

								and not the main one (e.g. user clocked "Ok" in a modal dialog), or some

								other combination: In these cases, C<ev_break> will not work alone.


								The solution is to maintain "break this loop" variable for each C<ev_run>

								invocation, and use a loop around C<ev_run> until the condition is

								triggered, using C<EVRUN_ONCE>:


								   // main loop

								   int exit_main_loop = 0;


								   while (!exit_main_loop)

								     ev_run (EV_DEFAULT_ EVRUN_ONCE);


								   // in a model watcher

								   int exit_nested_loop = 0;


								   while (!exit_nested_loop)

								     ev_run (EV_A_ EVRUN_ONCE);


								To exit from any of these loops, just set the corresponding exit variable:


								   // exit modal loop

								   exit_nested_loop = 1;


								   // exit main program, after modal loop is finished

								   exit_main_loop = 1;


								   // exit both

								   exit_main_loop = exit_nested_loop = 1;


								=head2 THREAD LOCKING EXAMPLE


								Here is a fictitious example of how to run an event loop in a different

								thread from where callbacks are being invoked and watchers are

								created/added/removed.


								For a real-world example, see the C<EV::Loop::Async> perl module,

								which uses exactly this technique (which is suited for many high-level

								languages).


								The example uses a pthread mutex to protect the loop data, a condition

								variable to wait for callback invocations, an async watcher to notify the

								event loop thread and an unspecified mechanism to wake up the main thread.


								First, you need to associate some data with the event loop:


								   typedef struct {

								     mutex_t lock; /* global loop lock */

								     ev_async async_w;

								     thread_t tid;

								     cond_t invoke_cv;

								   } userdata;


								   void prepare_loop (EV_P)

								   {

								      // for simplicity, we use a static userdata struct.

								      static userdata u;


								      ev_async_init (&u->async_w, async_cb);

								      ev_async_start (EV_A_ &u->async_w);


								      pthread_mutex_init (&u->lock, 0);

								      pthread_cond_init (&u->invoke_cv, 0);


								      // now associate this with the loop

								      ev_set_userdata (EV_A_ u);

								      ev_set_invoke_pending_cb (EV_A_ l_invoke);

								      ev_set_loop_release_cb (EV_A_ l_release, l_acquire);


								      // then create the thread running ev_run

								      pthread_create (&u->tid, 0, l_run, EV_A);

								   }


								The callback for the C<ev_async> watcher does nothing: the watcher is used

								solely to wake up the event loop so it takes notice of any new watchers

								that might have been added:


								   static void

								   async_cb (EV_P_ ev_async *w, int revents)

								   {

								      // just used for the side effects

								   }


								The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex

								protecting the loop data, respectively.


								   static void

								   l_release (EV_P)

								   {

								     userdata *u = ev_userdata (EV_A);

								     pthread_mutex_unlock (&u->lock);

								   }


								   static void

								   l_acquire (EV_P)

								   {

								     userdata *u = ev_userdata (EV_A);

								     pthread_mutex_lock (&u->lock);

								   }


								The event loop thread first acquires the mutex, and then jumps straight

								into C<ev_run>:


								   void *

								   l_run (void *thr_arg)

								   {

								     struct ev_loop *loop = (struct ev_loop *)thr_arg;


								     l_acquire (EV_A);

								     pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);

								     ev_run (EV_A_ 0);

								     l_release (EV_A);


								     return 0;

								   }


								Instead of invoking all pending watchers, the C<l_invoke> callback will

								signal the main thread via some unspecified mechanism (signals? pipe

								writes? C<Async::Interrupt>?) and then waits until all pending watchers

								have been called (in a while loop because a) spurious wakeups are possible

								and b) skipping inter-thread-communication when there are no pending

								watchers is very beneficial):


								   static void

								   l_invoke (EV_P)

								   {

								     userdata *u = ev_userdata (EV_A);


								     while (ev_pending_count (EV_A))

								       {

								         wake_up_other_thread_in_some_magic_or_not_so_magic_way ();

								         pthread_cond_wait (&u->invoke_cv, &u->lock);

								       }

								   }


								Now, whenever the main thread gets told to invoke pending watchers, it

								will grab the lock, call C<ev_invoke_pending> and then signal the loop

								thread to continue:


								   static void

								   real_invoke_pending (EV_P)

								   {

								     userdata *u = ev_userdata (EV_A);


								     pthread_mutex_lock (&u->lock);

								     ev_invoke_pending (EV_A);

								     pthread_cond_signal (&u->invoke_cv);

								     pthread_mutex_unlock (&u->lock);

								   }


								Whenever you want to start/stop a watcher or do other modifications to an

								event loop, you will now have to lock:


								   ev_timer timeout_watcher;

								   userdata *u = ev_userdata (EV_A);


								   ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);


								   pthread_mutex_lock (&u->lock);

								   ev_timer_start (EV_A_ &timeout_watcher);

								   ev_async_send (EV_A_ &u->async_w);

								   pthread_mutex_unlock (&u->lock);


								Note that sending the C<ev_async> watcher is required because otherwise

								an event loop currently blocking in the kernel will have no knowledge

								about the newly added timer. By waking up the loop it will pick up any new

								watchers in the next event loop iteration.


								=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS


								While the overhead of a callback that e.g. schedules a thread is small, it

								is still an overhead. If you embed libev, and your main usage is with some

								kind of threads or coroutines, you might want to customise libev so that

								doesn't need callbacks anymore.


								Imagine you have coroutines that you can switch to using a function

								C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>

								and that due to some magic, the currently active coroutine is stored in a

								global called C<current_coro>. Then you can build your own "wait for libev

								event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note

								the differing C<;> conventions):


								   #define EV_CB_DECLARE(type)   struct my_coro *cb;

								   #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)


								That means instead of having a C callback function, you store the

								coroutine to switch to in each watcher, and instead of having libev call

								your callback, you instead have it switch to that coroutine.


								A coroutine might now wait for an event with a function called

								C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't

								matter when, or whether the watcher is active or not when this function is

								called):


								   void

								   wait_for_event (ev_watcher *w)

								   {

								     ev_cb_set (w) = current_coro;

								     switch_to (libev_coro);

								   }


								That basically suspends the coroutine inside C<wait_for_event> and

								continues the libev coroutine, which, when appropriate, switches back to

								this or any other coroutine. I am sure if you sue this your own :)


								You can do similar tricks if you have, say, threads with an event queue -

								instead of storing a coroutine, you store the queue object and instead of

								switching to a coroutine, you push the watcher onto the queue and notify

								any waiters.


								To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two

								files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:


								   // my_ev.h

								   #define EV_CB_DECLARE(type)   struct my_coro *cb;

								   #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);

								   #include "../libev/ev.h"


								   // my_ev.c

								   #define EV_H "my_ev.h"

								   #include "../libev/ev.c"


								And then use F<my_ev.h> when you would normally use F<ev.h>, and compile

								F<my_ev.c> into your project. When properly specifying include paths, you

								can even use F<ev.h> as header file name directly.


								=head1 LIBEVENT EMULATION


								Libev offers a compatibility emulation layer for libevent. It cannot

								emulate the internals of libevent, so here are some usage hints:


								=over 4


								=item * Only the libevent-1.4.1-beta API is being emulated.


								This was the newest libevent version available when libev was implemented,

								and is still mostly unchanged in 2010.


								=item * Use it by including <event.h>, as usual.


								=item * The following members are fully supported: ev_base, ev_callback,

								ev_arg, ev_fd, ev_res, ev_events.


								=item * Avoid using ev_flags and the EVLIST_*-macros, while it is

								maintained by libev, it does not work exactly the same way as in libevent (consider

								it a private API).


								=item * Priorities are not currently supported. Initialising priorities

								will fail and all watchers will have the same priority, even though there

								is an ev_pri field.


								=item * In libevent, the last base created gets the signals, in libev, the

								base that registered the signal gets the signals.


								=item * Other members are not supported.


								=item * The libev emulation is I<not> ABI compatible to libevent, you need

								to use the libev header file and library.


								=back


								=head1 C++ SUPPORT


								Libev comes with some simplistic wrapper classes for C++ that mainly allow

								you to use some convenience methods to start/stop watchers and also change

								the callback model to a model using method callbacks on objects.


								To use it,


								   #include <ev++.h>


								This automatically includes F<ev.h> and puts all of its definitions (many

								of them macros) into the global namespace. All C++ specific things are

								put into the C<ev> namespace. It should support all the same embedding

								options as F<ev.h>, most notably C<EV_MULTIPLICITY>.


								Care has been taken to keep the overhead low. The only data member the C++

								classes add (compared to plain C-style watchers) is the event loop pointer

								that the watcher is associated with (or no additional members at all if

								you disable C<EV_MULTIPLICITY> when embedding libev).


								Currently, functions, static and non-static member functions and classes

								with C<operator ()> can be used as callbacks. Other types should be easy

								to add as long as they only need one additional pointer for context. If

								you need support for other types of functors please contact the author

								(preferably after implementing it).


								Here is a list of things available in the C<ev> namespace:


								=over 4


								=item C<ev::READ>, C<ev::WRITE> etc.


								These are just enum values with the same values as the C<EV_READ> etc.

								macros from F<ev.h>.


								=item C<ev::tstamp>, C<ev::now>


								Aliases to the same types/functions as with the C<ev_> prefix.


								=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.


								For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of

								the same name in the C<ev> namespace, with the exception of C<ev_signal>

								which is called C<ev::sig> to avoid clashes with the C<signal> macro

								defines by many implementations.


								All of those classes have these methods:


								=over 4


								=item ev::TYPE::TYPE ()


								=item ev::TYPE::TYPE (loop)


								=item ev::TYPE::~TYPE


								The constructor (optionally) takes an event loop to associate the watcher

								with. If it is omitted, it will use C<EV_DEFAULT>.


								The constructor calls C<ev_init> for you, which means you have to call the

								C<set> method before starting it.


								It will not set a callback, however: You have to call the templated C<set>

								method to set a callback before you can start the watcher.


								(The reason why you have to use a method is a limitation in C++ which does

								not allow explicit template arguments for constructors).


								The destructor automatically stops the watcher if it is active.


								=item w->set<class, &class::method> (object *)


								This method sets the callback method to call. The method has to have a

								signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as

								first argument and the C<revents> as second. The object must be given as

								parameter and is stored in the C<data> member of the watcher.


								This method synthesizes efficient thunking code to call your method from

								the C callback that libev requires. If your compiler can inline your

								callback (i.e. it is visible to it at the place of the C<set> call and

								your compiler is good :), then the method will be fully inlined into the

								thunking function, making it as fast as a direct C callback.


								Example: simple class declaration and watcher initialisation


								   struct myclass

								   {

								     void io_cb (ev::io &w, int revents) { }

								   }


								   myclass obj;

								   ev::io iow;

								   iow.set <myclass, &myclass::io_cb> (&obj);


								=item w->set (object *)


								This is a variation of a method callback - leaving out the method to call

								will default the method to C<operator ()>, which makes it possible to use

								functor objects without having to manually specify the C<operator ()> all

								the time. Incidentally, you can then also leave out the template argument

								list.


								The C<operator ()> method prototype must be C<void operator ()(watcher &w,

								int revents)>.


								See the method-C<set> above for more details.


								Example: use a functor object as callback.


								   struct myfunctor

								   {

								     void operator() (ev::io &w, int revents)

								     {

								       ...

								     }

								   }


								   myfunctor f;


								   ev::io w;

								   w.set (&f);


								=item w->set<function> (void *data = 0)


								Also sets a callback, but uses a static method or plain function as

								callback. The optional C<data> argument will be stored in the watcher's

								C<data> member and is free for you to use.


								The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.


								See the method-C<set> above for more details.


								Example: Use a plain function as callback.


								   static void io_cb (ev::io &w, int revents) { }

								   iow.set <io_cb> ();


								=item w->set (loop)


								Associates a different C<struct ev_loop> with this watcher. You can only

								do this when the watcher is inactive (and not pending either).


								=item w->set ([arguments])


								Basically the same as C<ev_TYPE_set>, with the same arguments. Either this

								method or a suitable start method must be called at least once. Unlike the

								C counterpart, an active watcher gets automatically stopped and restarted

								when reconfiguring it with this method.


								=item w->start ()


								Starts the watcher. Note that there is no C<loop> argument, as the

								constructor already stores the event loop.


								=item w->start ([arguments])


								Instead of calling C<set> and C<start> methods separately, it is often

								convenient to wrap them in one call. Uses the same type of arguments as

								the configure C<set> method of the watcher.


								=item w->stop ()


								Stops the watcher if it is active. Again, no C<loop> argument.


								=item w->again () (C<ev::timer>, C<ev::periodic> only)


								For C<ev::timer> and C<ev::periodic>, this invokes the corresponding

								C<ev_TYPE_again> function.


								=item w->sweep () (C<ev::embed> only)


								Invokes C<ev_embed_sweep>.


								=item w->update () (C<ev::stat> only)


								Invokes C<ev_stat_stat>.


								=back


								=back


								Example: Define a class with two I/O and idle watchers, start the I/O

								watchers in the constructor.


								   class myclass

								   {

								     ev::io   io  ; void io_cb   (ev::io   &w, int revents);

								     ev::io2  io2 ; void io2_cb  (ev::io   &w, int revents);

								     ev::idle idle; void idle_cb (ev::idle &w, int revents);


								     myclass (int fd)

								     {

								       io  .set <myclass, &myclass::io_cb  > (this);

								       io2 .set <myclass, &myclass::io2_cb > (this);

								       idle.set <myclass, &myclass::idle_cb> (this);


								       io.set (fd, ev::WRITE); // configure the watcher

								       io.start ();            // start it whenever convenient


								       io2.start (fd, ev::READ); // set + start in one call

								     }

								   };


								=head1 OTHER LANGUAGE BINDINGS


								Libev does not offer other language bindings itself, but bindings for a

								number of languages exist in the form of third-party packages. If you know

								any interesting language binding in addition to the ones listed here, drop

								me a note.


								=over 4


								=item Perl


								The EV module implements the full libev API and is actually used to test

								libev. EV is developed together with libev. Apart from the EV core module,

								there are additional modules that implement libev-compatible interfaces

								to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),

								C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>

								and C<EV::Glib>).


								It can be found and installed via CPAN, its homepage is at

								L<http://software.schmorp.de/pkg/EV>.


								=item Python


								Python bindings can be found at L<http://code.google.com/p/pyev/>. It

								seems to be quite complete and well-documented.


								=item Ruby


								Tony Arcieri has written a ruby extension that offers access to a subset

								of the libev API and adds file handle abstractions, asynchronous DNS and

								more on top of it. It can be found via gem servers. Its homepage is at

								L<http://rev.rubyforge.org/>.


								Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>

								makes rev work even on mingw.


								=item Haskell


								A haskell binding to libev is available at

								L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.


								=item D


								Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to

								be found at L<http://proj.llucax.com.ar/wiki/evd>.


								=item Ocaml


								Erkki Seppala has written Ocaml bindings for libev, to be found at

								L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.


								=item Lua


								Brian Maher has written a partial interface to libev for lua (at the

								time of this writing, only C<ev_io> and C<ev_timer>), to be found at

								L<http://github.com/brimworks/lua-ev>.


								=back


								=head1 MACRO MAGIC


								Libev can be compiled with a variety of options, the most fundamental

								of which is C<EV_MULTIPLICITY>. This option determines whether (most)

								functions and callbacks have an initial C<struct ev_loop *> argument.


								To make it easier to write programs that cope with either variant, the

								following macros are defined:


								=over 4


								=item C<EV_A>, C<EV_A_>


								This provides the loop I<argument> for functions, if one is required ("ev

								loop argument"). The C<EV_A> form is used when this is the sole argument,

								C<EV_A_> is used when other arguments are following. Example:


								   ev_unref (EV_A);

								   ev_timer_add (EV_A_ watcher);

								   ev_run (EV_A_ 0);


								It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,

								which is often provided by the following macro.


								=item C<EV_P>, C<EV_P_>


								This provides the loop I<parameter> for functions, if one is required ("ev

								loop parameter"). The C<EV_P> form is used when this is the sole parameter,

								C<EV_P_> is used when other parameters are following. Example:


								   // this is how ev_unref is being declared

								   static void ev_unref (EV_P);


								   // this is how you can declare your typical callback

								   static void cb (EV_P_ ev_timer *w, int revents)


								It declares a parameter C<loop> of type C<struct ev_loop *>, quite

								suitable for use with C<EV_A>.


								=item C<EV_DEFAULT>, C<EV_DEFAULT_>


								Similar to the other two macros, this gives you the value of the default

								loop, if multiple loops are supported ("ev loop default").


								=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>


								Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the

								default loop has been initialised (C<UC> == unchecked). Their behaviour

								is undefined when the default loop has not been initialised by a previous

								execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.


								It is often prudent to use C<EV_DEFAULT> when initialising the first

								watcher in a function but use C<EV_DEFAULT_UC> afterwards.


								=back


								Example: Declare and initialise a check watcher, utilising the above

								macros so it will work regardless of whether multiple loops are supported

								or not.


								   static void

								   check_cb (EV_P_ ev_timer *w, int revents)

								   {

								     ev_check_stop (EV_A_ w);

								   }


								   ev_check check;

								   ev_check_init (&check, check_cb);

								   ev_check_start (EV_DEFAULT_ &check);

								   ev_run (EV_DEFAULT_ 0);


								=head1 EMBEDDING


								Libev can (and often is) directly embedded into host

								applications. Examples of applications that embed it include the Deliantra

								Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)

								and rxvt-unicode.


								The goal is to enable you to just copy the necessary files into your

								source directory without having to change even a single line in them, so

								you can easily upgrade by simply copying (or having a checked-out copy of

								libev somewhere in your source tree).


								=head2 FILESETS


								Depending on what features you need you need to include one or more sets of files

								in your application.


								=head3 CORE EVENT LOOP


								To include only the libev core (all the C<ev_*> functions), with manual

								configuration (no autoconf):


								   #define EV_STANDALONE 1

								   #include "ev.c"


								This will automatically include F<ev.h>, too, and should be done in a

								single C source file only to provide the function implementations. To use

								it, do the same for F<ev.h> in all files wishing to use this API (best

								done by writing a wrapper around F<ev.h> that you can include instead and

								where you can put other configuration options):


								   #define EV_STANDALONE 1

								   #include "ev.h"


								Both header files and implementation files can be compiled with a C++

								compiler (at least, that's a stated goal, and breakage will be treated

								as a bug).


								You need the following files in your source tree, or in a directory

								in your include path (e.g. in libev/ when using -Ilibev):


								   ev.h

								   ev.c

								   ev_vars.h

								   ev_wrap.h


								   ev_win32.c      required on win32 platforms only


								   ev_select.c     only when select backend is enabled (which is enabled by default)

								   ev_poll.c       only when poll backend is enabled (disabled by default)

								   ev_epoll.c      only when the epoll backend is enabled (disabled by default)

								   ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)

								   ev_port.c       only when the solaris port backend is enabled (disabled by default)


								F<ev.c> includes the backend files directly when enabled, so you only need

								to compile this single file.


								=head3 LIBEVENT COMPATIBILITY API


								To include the libevent compatibility API, also include:


								   #include "event.c"


								in the file including F<ev.c>, and:


								   #include "event.h"


								in the files that want to use the libevent API. This also includes F<ev.h>.


								You need the following additional files for this:


								   event.h

								   event.c


								=head3 AUTOCONF SUPPORT


								Instead of using C<EV_STANDALONE=1> and providing your configuration in

								whatever way you want, you can also C<m4_include([libev.m4])> in your

								F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then

								include F<config.h> and configure itself accordingly.


								For this of course you need the m4 file:


								   libev.m4


								=head2 PREPROCESSOR SYMBOLS/MACROS


								Libev can be configured via a variety of preprocessor symbols you have to

								define before including (or compiling) any of its files. The default in

								the absence of autoconf is documented for every option.


								Symbols marked with "(h)" do not change the ABI, and can have different

								values when compiling libev vs. including F<ev.h>, so it is permissible

								to redefine them before including F<ev.h> without breaking compatibility

								to a compiled library. All other symbols change the ABI, which means all

								users of libev and the libev code itself must be compiled with compatible

								settings.


								=over 4


								=item EV_COMPAT3 (h)


								Backwards compatibility is a major concern for libev. This is why this

								release of libev comes with wrappers for the functions and symbols that

								have been renamed between libev version 3 and 4.


								You can disable these wrappers (to test compatibility with future

								versions) by defining C<EV_COMPAT3> to C<0> when compiling your

								sources. This has the additional advantage that you can drop the C<struct>

								from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>

								typedef in that case.


								In some future version, the default for C<EV_COMPAT3> will become C<0>,

								and in some even more future version the compatibility code will be

								removed completely.


								=item EV_STANDALONE (h)


								Must always be C<1> if you do not use autoconf configuration, which

								keeps libev from including F<config.h>, and it also defines dummy

								implementations for some libevent functions (such as logging, which is not

								supported). It will also not define any of the structs usually found in

								F<event.h> that are not directly supported by the libev core alone.


								In standalone mode, libev will still try to automatically deduce the

								configuration, but has to be more conservative.


								=item EV_USE_MONOTONIC


								If defined to be C<1>, libev will try to detect the availability of the

								monotonic clock option at both compile time and runtime. Otherwise no

								use of the monotonic clock option will be attempted. If you enable this,

								you usually have to link against librt or something similar. Enabling it

								when the functionality isn't available is safe, though, although you have

								to make sure you link against any libraries where the C<clock_gettime>

								function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.


								=item EV_USE_REALTIME


								If defined to be C<1>, libev will try to detect the availability of the

								real-time clock option at compile time (and assume its availability

								at runtime if successful). Otherwise no use of the real-time clock

								option will be attempted. This effectively replaces C<gettimeofday>

								by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect

								correctness. See the note about libraries in the description of

								C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of

								C<EV_USE_CLOCK_SYSCALL>.


								=item EV_USE_CLOCK_SYSCALL


								If defined to be C<1>, libev will try to use a direct syscall instead

								of calling the system-provided C<clock_gettime> function. This option

								exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>

								unconditionally pulls in C<libpthread>, slowing down single-threaded

								programs needlessly. Using a direct syscall is slightly slower (in

								theory), because no optimised vdso implementation can be used, but avoids

								the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or

								higher, as it simplifies linking (no need for C<-lrt>).


								=item EV_USE_NANOSLEEP


								If defined to be C<1>, libev will assume that C<nanosleep ()> is available

								and will use it for delays. Otherwise it will use C<select ()>.


								=item EV_USE_EVENTFD


								If defined to be C<1>, then libev will assume that C<eventfd ()> is

								available and will probe for kernel support at runtime. This will improve

								C<ev_signal> and C<ev_async> performance and reduce resource consumption.

								If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc

								2.7 or newer, otherwise disabled.


								=item EV_USE_SELECT


								If undefined or defined to be C<1>, libev will compile in support for the

								C<select>(2) backend. No attempt at auto-detection will be done: if no

								other method takes over, select will be it. Otherwise the select backend

								will not be compiled in.


								=item EV_SELECT_USE_FD_SET


								If defined to C<1>, then the select backend will use the system C<fd_set>

								structure. This is useful if libev doesn't compile due to a missing

								C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout

								on exotic systems. This usually limits the range of file descriptors to

								some low limit such as 1024 or might have other limitations (winsocket

								only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,

								configures the maximum size of the C<fd_set>.


								=item EV_SELECT_IS_WINSOCKET


								When defined to C<1>, the select backend will assume that

								select/socket/connect etc. don't understand file descriptors but

								wants osf handles on win32 (this is the case when the select to

								be used is the winsock select). This means that it will call

								C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,

								it is assumed that all these functions actually work on fds, even

								on win32. Should not be defined on non-win32 platforms.


								=item EV_FD_TO_WIN32_HANDLE(fd)


								If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map

								file descriptors to socket handles. When not defining this symbol (the

								default), then libev will call C<_get_osfhandle>, which is usually

								correct. In some cases, programs use their own file descriptor management,

								in which case they can provide this function to map fds to socket handles.


								=item EV_WIN32_HANDLE_TO_FD(handle)


								If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors

								using the standard C<_open_osfhandle> function. For programs implementing

								their own fd to handle mapping, overwriting this function makes it easier

								to do so. This can be done by defining this macro to an appropriate value.


								=item EV_WIN32_CLOSE_FD(fd)


								If programs implement their own fd to handle mapping on win32, then this

								macro can be used to override the C<close> function, useful to unregister

								file descriptors again. Note that the replacement function has to close

								the underlying OS handle.


								=item EV_USE_POLL


								If defined to be C<1>, libev will compile in support for the C<poll>(2)

								backend. Otherwise it will be enabled on non-win32 platforms. It

								takes precedence over select.


								=item EV_USE_EPOLL


								If defined to be C<1>, libev will compile in support for the Linux

								C<epoll>(7) backend. Its availability will be detected at runtime,

								otherwise another method will be used as fallback. This is the preferred

								backend for GNU/Linux systems. If undefined, it will be enabled if the

								headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.


								=item EV_USE_KQUEUE


								If defined to be C<1>, libev will compile in support for the BSD style

								C<kqueue>(2) backend. Its actual availability will be detected at runtime,

								otherwise another method will be used as fallback. This is the preferred

								backend for BSD and BSD-like systems, although on most BSDs kqueue only

								supports some types of fds correctly (the only platform we found that

								supports ptys for example was NetBSD), so kqueue might be compiled in, but

								not be used unless explicitly requested. The best way to use it is to find

								out whether kqueue supports your type of fd properly and use an embedded

								kqueue loop.


								=item EV_USE_PORT


								If defined to be C<1>, libev will compile in support for the Solaris

								10 port style backend. Its availability will be detected at runtime,

								otherwise another method will be used as fallback. This is the preferred

								backend for Solaris 10 systems.


								=item EV_USE_DEVPOLL


								Reserved for future expansion, works like the USE symbols above.


								=item EV_USE_INOTIFY


								If defined to be C<1>, libev will compile in support for the Linux inotify

								interface to speed up C<ev_stat> watchers. Its actual availability will

								be detected at runtime. If undefined, it will be enabled if the headers

								indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.


								=item EV_ATOMIC_T


								Libev requires an integer type (suitable for storing C<0> or C<1>) whose

								access is atomic with respect to other threads or signal contexts. No such

								type is easily found in the C language, so you can provide your own type

								that you know is safe for your purposes. It is used both for signal handler "locking"

								as well as for signal and thread safety in C<ev_async> watchers.


								In the absence of this define, libev will use C<sig_atomic_t volatile>

								(from F<signal.h>), which is usually good enough on most platforms.


								=item EV_H (h)


								The name of the F<ev.h> header file used to include it. The default if

								undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be

								used to virtually rename the F<ev.h> header file in case of conflicts.


								=item EV_CONFIG_H (h)


								If C<EV_STANDALONE> isn't C<1>, this variable can be used to override

								F<ev.c>'s idea of where to find the F<config.h> file, similarly to

								C<EV_H>, above.


								=item EV_EVENT_H (h)


								Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea

								of how the F<event.h> header can be found, the default is C<"event.h">.


								=item EV_PROTOTYPES (h)


								If defined to be C<0>, then F<ev.h> will not define any function

								prototypes, but still define all the structs and other symbols. This is

								occasionally useful if you want to provide your own wrapper functions

								around libev functions.


								=item EV_MULTIPLICITY


								If undefined or defined to C<1>, then all event-loop-specific functions

								will have the C<struct ev_loop *> as first argument, and you can create

								additional independent event loops. Otherwise there will be no support

								for multiple event loops and there is no first event loop pointer

								argument. Instead, all functions act on the single default loop.


								=item EV_MINPRI


								=item EV_MAXPRI


								The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to

								C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can

								provide for more priorities by overriding those symbols (usually defined

								to be C<-2> and C<2>, respectively).


								When doing priority-based operations, libev usually has to linearly search

								all the priorities, so having many of them (hundreds) uses a lot of space

								and time, so using the defaults of five priorities (-2 .. +2) is usually

								fine.


								If your embedding application does not need any priorities, defining these

								both to C<0> will save some memory and CPU.


								=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,

								EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,

								EV_ASYNC_ENABLE, EV_CHILD_ENABLE.


								If undefined or defined to be C<1> (and the platform supports it), then

								the respective watcher type is supported. If defined to be C<0>, then it

								is not. Disabling watcher types mainly saves code size.


								=item EV_FEATURES


								If you need to shave off some kilobytes of code at the expense of some

								speed (but with the full API), you can define this symbol to request

								certain subsets of functionality. The default is to enable all features

								that can be enabled on the platform.


								A typical way to use this symbol is to define it to C<0> (or to a bitset

								with some broad features you want) and then selectively re-enable

								additional parts you want, for example if you want everything minimal,

								but multiple event loop support, async and child watchers and the poll

								backend, use this:


								   #define EV_FEATURES 0

								   #define EV_MULTIPLICITY 1

								   #define EV_USE_POLL 1

								   #define EV_CHILD_ENABLE 1

								   #define EV_ASYNC_ENABLE 1


								The actual value is a bitset, it can be a combination of the following

								values:


								=over 4


								=item C<1> - faster/larger code


								Use larger code to speed up some operations.


								Currently this is used to override some inlining decisions (enlarging the

								code size by roughly 30% on amd64).


								When optimising for size, use of compiler flags such as C<-Os> with

								gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of

								assertions.


								=item C<2> - faster/larger data structures


								Replaces the small 2-heap for timer management by a faster 4-heap, larger

								hash table sizes and so on. This will usually further increase code size

								and can additionally have an effect on the size of data structures at

								runtime.


								=item C<4> - full API configuration


								This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and

								enables multiplicity (C<EV_MULTIPLICITY>=1).


								=item C<8> - full API


								This enables a lot of the "lesser used" API functions. See C<ev.h> for

								details on which parts of the API are still available without this

								feature, and do not complain if this subset changes over time.


								=item C<16> - enable all optional watcher types


								Enables all optional watcher types.  If you want to selectively enable

								only some watcher types other than I/O and timers (e.g. prepare,

								embed, async, child...) you can enable them manually by defining

								C<EV_watchertype_ENABLE> to C<1> instead.


								=item C<32> - enable all backends


								This enables all backends - without this feature, you need to enable at

								least one backend manually (C<EV_USE_SELECT> is a good choice).


								=item C<64> - enable OS-specific "helper" APIs


								Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by

								default.


								=back


								Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>

								reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb

								code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O

								watchers, timers and monotonic clock support.


								With an intelligent-enough linker (gcc+binutils are intelligent enough

								when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by

								your program might be left out as well - a binary starting a timer and an

								I/O watcher then might come out at only 5Kb.


								=item EV_AVOID_STDIO


								If this is set to C<1> at compiletime, then libev will avoid using stdio

								functions (printf, scanf, perror etc.). This will increase the code size

								somewhat, but if your program doesn't otherwise depend on stdio and your

								libc allows it, this avoids linking in the stdio library which is quite

								big.


								Note that error messages might become less precise when this option is

								enabled.


								=item EV_NSIG


								The highest supported signal number, +1 (or, the number of

								signals): Normally, libev tries to deduce the maximum number of signals

								automatically, but sometimes this fails, in which case it can be

								specified. Also, using a lower number than detected (C<32> should be

								good for about any system in existence) can save some memory, as libev

								statically allocates some 12-24 bytes per signal number.


								=item EV_PID_HASHSIZE


								C<ev_child> watchers use a small hash table to distribute workload by

								pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),

								usually more than enough. If you need to manage thousands of children you

								might want to increase this value (I<must> be a power of two).


								=item EV_INOTIFY_HASHSIZE


								C<ev_stat> watchers use a small hash table to distribute workload by

								inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>

								disabled), usually more than enough. If you need to manage thousands of

								C<ev_stat> watchers you might want to increase this value (I<must> be a

								power of two).


								=item EV_USE_4HEAP


								Heaps are not very cache-efficient. To improve the cache-efficiency of the

								timer and periodics heaps, libev uses a 4-heap when this symbol is defined

								to C<1>. The 4-heap uses more complicated (longer) code but has noticeably

								faster performance with many (thousands) of watchers.


								The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it

								will be C<0>.


								=item EV_HEAP_CACHE_AT


								Heaps are not very cache-efficient. To improve the cache-efficiency of the

								timer and periodics heaps, libev can cache the timestamp (I<at>) within

								the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),

								which uses 8-12 bytes more per watcher and a few hundred bytes more code,

								but avoids random read accesses on heap changes. This improves performance

								noticeably with many (hundreds) of watchers.


								The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it

								will be C<0>.


								=item EV_VERIFY


								Controls how much internal verification (see C<ev_verify ()>) will

								be done: If set to C<0>, no internal verification code will be compiled

								in. If set to C<1>, then verification code will be compiled in, but not

								called. If set to C<2>, then the internal verification code will be

								called once per loop, which can slow down libev. If set to C<3>, then the

								verification code will be called very frequently, which will slow down

								libev considerably.


								The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it

								will be C<0>.


								=item EV_COMMON


								By default, all watchers have a C<void *data> member. By redefining

								this macro to something else you can include more and other types of

								members. You have to define it each time you include one of the files,

								though, and it must be identical each time.


								For example, the perl EV module uses something like this:


								   #define EV_COMMON                       \

								     SV *self; /* contains this struct */  \

								     SV *cb_sv, *fh /* note no trailing ";" */


								=item EV_CB_DECLARE (type)


								=item EV_CB_INVOKE (watcher, revents)


								=item ev_set_cb (ev, cb)


								Can be used to change the callback member declaration in each watcher,

								and the way callbacks are invoked and set. Must expand to a struct member

								definition and a statement, respectively. See the F<ev.h> header file for

								their default definitions. One possible use for overriding these is to

								avoid the C<struct ev_loop *> as first argument in all cases, or to use

								method calls instead of plain function calls in C++.


								=back


								=head2 EXPORTED API SYMBOLS


								If you need to re-export the API (e.g. via a DLL) and you need a list of

								exported symbols, you can use the provided F<Symbol.*> files which list

								all public symbols, one per line:


								   Symbols.ev      for libev proper

								   Symbols.event   for the libevent emulation


								This can also be used to rename all public symbols to avoid clashes with

								multiple versions of libev linked together (which is obviously bad in

								itself, but sometimes it is inconvenient to avoid this).


								A sed command like this will create wrapper C<#define>'s that you need to

								include before including F<ev.h>:


								   <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h


								This would create a file F<wrap.h> which essentially looks like this:


								   #define ev_backend     myprefix_ev_backend

								   #define ev_check_start myprefix_ev_check_start

								   #define ev_check_stop  myprefix_ev_check_stop

								   ...


								=head2 EXAMPLES


								For a real-world example of a program the includes libev

								verbatim, you can have a look at the EV perl module

								(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in

								the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public

								interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file

								will be compiled. It is pretty complex because it provides its own header

								file.


								The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file

								that everybody includes and which overrides some configure choices:


								   #define EV_FEATURES 8

								   #define EV_USE_SELECT 1

								   #define EV_PREPARE_ENABLE 1

								   #define EV_IDLE_ENABLE 1

								   #define EV_SIGNAL_ENABLE 1

								   #define EV_CHILD_ENABLE 1

								   #define EV_USE_STDEXCEPT 0

								   #define EV_CONFIG_H <config.h>


								   #include "ev++.h"


								And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:


								   #include "ev_cpp.h"

								   #include "ev.c"


								=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT


								=head2 THREADS AND COROUTINES


								=head3 THREADS


								All libev functions are reentrant and thread-safe unless explicitly

								documented otherwise, but libev implements no locking itself. This means

								that you can use as many loops as you want in parallel, as long as there

								are no concurrent calls into any libev function with the same loop

								parameter (C<ev_default_*> calls have an implicit default loop parameter,

								of course): libev guarantees that different event loops share no data

								structures that need any locking.


								Or to put it differently: calls with different loop parameters can be done

								concurrently from multiple threads, calls with the same loop parameter

								must be done serially (but can be done from different threads, as long as

								only one thread ever is inside a call at any point in time, e.g. by using

								a mutex per loop).


								Specifically to support threads (and signal handlers), libev implements

								so-called C<ev_async> watchers, which allow some limited form of

								concurrency on the same event loop, namely waking it up "from the

								outside".


								If you want to know which design (one loop, locking, or multiple loops

								without or something else still) is best for your problem, then I cannot

								help you, but here is some generic advice:


								=over 4


								=item * most applications have a main thread: use the default libev loop

								in that thread, or create a separate thread running only the default loop.


								This helps integrating other libraries or software modules that use libev

								themselves and don't care/know about threading.


								=item * one loop per thread is usually a good model.


								Doing this is almost never wrong, sometimes a better-performance model

								exists, but it is always a good start.


								=item * other models exist, such as the leader/follower pattern, where one

								loop is handed through multiple threads in a kind of round-robin fashion.


								Choosing a model is hard - look around, learn, know that usually you can do

								better than you currently do :-)


								=item * often you need to talk to some other thread which blocks in the

								event loop.


								C<ev_async> watchers can be used to wake them up from other threads safely

								(or from signal contexts...).


								An example use would be to communicate signals or other events that only

								work in the default loop by registering the signal watcher with the

								default loop and triggering an C<ev_async> watcher from the default loop

								watcher callback into the event loop interested in the signal.


								=back


								See also L<THREAD LOCKING EXAMPLE>.


								=head3 COROUTINES


								Libev is very accommodating to coroutines ("cooperative threads"):

								libev fully supports nesting calls to its functions from different

								coroutines (e.g. you can call C<ev_run> on the same loop from two

								different coroutines, and switch freely between both coroutines running

								the loop, as long as you don't confuse yourself). The only exception is

								that you must not do this from C<ev_periodic> reschedule callbacks.


								Care has been taken to ensure that libev does not keep local state inside

								C<ev_run>, and other calls do not usually allow for coroutine switches as

								they do not call any callbacks.


								=head2 COMPILER WARNINGS


								Depending on your compiler and compiler settings, you might get no or a

								lot of warnings when compiling libev code. Some people are apparently

								scared by this.


								However, these are unavoidable for many reasons. For one, each compiler

								has different warnings, and each user has different tastes regarding

								warning options. "Warn-free" code therefore cannot be a goal except when

								targeting a specific compiler and compiler-version.


								Another reason is that some compiler warnings require elaborate

								workarounds, or other changes to the code that make it less clear and less

								maintainable.


								And of course, some compiler warnings are just plain stupid, or simply

								wrong (because they don't actually warn about the condition their message

								seems to warn about). For example, certain older gcc versions had some

								warnings that resulted in an extreme number of false positives. These have

								been fixed, but some people still insist on making code warn-free with

								such buggy versions.


								While libev is written to generate as few warnings as possible,

								"warn-free" code is not a goal, and it is recommended not to build libev

								with any compiler warnings enabled unless you are prepared to cope with

								them (e.g. by ignoring them). Remember that warnings are just that:

								warnings, not errors, or proof of bugs.


								=head2 VALGRIND


								Valgrind has a special section here because it is a popular tool that is

								highly useful. Unfortunately, valgrind reports are very hard to interpret.


								If you think you found a bug (memory leak, uninitialised data access etc.)

								in libev, then check twice: If valgrind reports something like:


								   ==2274==    definitely lost: 0 bytes in 0 blocks.

								   ==2274==      possibly lost: 0 bytes in 0 blocks.

								   ==2274==    still reachable: 256 bytes in 1 blocks.


								Then there is no memory leak, just as memory accounted to global variables

								is not a memleak - the memory is still being referenced, and didn't leak.


								Similarly, under some circumstances, valgrind might report kernel bugs

								as if it were a bug in libev (e.g. in realloc or in the poll backend,

								although an acceptable workaround has been found here), or it might be

								confused.


								Keep in mind that valgrind is a very good tool, but only a tool. Don't

								make it into some kind of religion.


								If you are unsure about something, feel free to contact the mailing list

								with the full valgrind report and an explanation on why you think this

								is a bug in libev (best check the archives, too :). However, don't be

								annoyed when you get a brisk "this is no bug" answer and take the chance

								of learning how to interpret valgrind properly.


								If you need, for some reason, empty reports from valgrind for your project

								I suggest using suppression lists.


								=head1 PORTABILITY NOTES


								=head2 GNU/LINUX 32 BIT LIMITATIONS


								GNU/Linux is the only common platform that supports 64 bit file/large file

								interfaces but I<disables> them by default.


								That means that libev compiled in the default environment doesn't support

								files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.


								Unfortunately, many programs try to work around this GNU/Linux issue

								by enabling the large file API, which makes them incompatible with the

								standard libev compiled for their system.


								Likewise, libev cannot enable the large file API itself as this would

								suddenly make it incompatible to the default compile time environment,

								i.e. all programs not using special compile switches.


								=head2 OS/X AND DARWIN BUGS


								The whole thing is a bug if you ask me - basically any system interface

								you touch is broken, whether it is locales, poll, kqueue or even the

								OpenGL drivers.


								=head3 C<kqueue> is buggy


								The kqueue syscall is broken in all known versions - most versions support

								only sockets, many support pipes.


								Libev tries to work around this by not using C<kqueue> by default on this

								rotten platform, but of course you can still ask for it when creating a

								loop - embedding a socket-only kqueue loop into a select-based one is

								probably going to work well.


								=head3 C<poll> is buggy


								Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>

								implementation by something calling C<kqueue> internally around the 10.5.6

								release, so now C<kqueue> I<and> C<poll> are broken.


								Libev tries to work around this by not using C<poll> by default on

								this rotten platform, but of course you can still ask for it when creating

								a loop.


								=head3 C<select> is buggy


								All that's left is C<select>, and of course Apple found a way to fuck this

								one up as well: On OS/X, C<select> actively limits the number of file

								descriptors you can pass in to 1024 - your program suddenly crashes when

								you use more.


								There is an undocumented "workaround" for this - defining

								C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>

								work on OS/X.


								=head2 SOLARIS PROBLEMS AND WORKAROUNDS


								=head3 C<errno> reentrancy


								The default compile environment on Solaris is unfortunately so

								thread-unsafe that you can't even use components/libraries compiled

								without C<-D_REENTRANT> in a threaded program, which, of course, isn't

								defined by default. A valid, if stupid, implementation choice.


								If you want to use libev in threaded environments you have to make sure

								it's compiled with C<_REENTRANT> defined.


								=head3 Event port backend


								The scalable event interface for Solaris is called "event

								ports". Unfortunately, this mechanism is very buggy in all major

								releases. If you run into high CPU usage, your program freezes or you get

								a large number of spurious wakeups, make sure you have all the relevant

								and latest kernel patches applied. No, I don't know which ones, but there

								are multiple ones to apply, and afterwards, event ports actually work

								great.


								If you can't get it to work, you can try running the program by setting

								the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and

								C<select> backends.


								=head2 AIX POLL BUG


								AIX unfortunately has a broken C<poll.h> header. Libev works around

								this by trying to avoid the poll backend altogether (i.e. it's not even

								compiled in), which normally isn't a big problem as C<select> works fine

								with large bitsets on AIX, and AIX is dead anyway.


								=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS


								=head3 General issues


								Win32 doesn't support any of the standards (e.g. POSIX) that libev

								requires, and its I/O model is fundamentally incompatible with the POSIX

								model. Libev still offers limited functionality on this platform in

								the form of the C<EVBACKEND_SELECT> backend, and only supports socket

								descriptors. This only applies when using Win32 natively, not when using

								e.g. cygwin. Actually, it only applies to the microsofts own compilers,

								as every compielr comes with a slightly differently broken/incompatible

								environment.


								Lifting these limitations would basically require the full

								re-implementation of the I/O system. If you are into this kind of thing,

								then note that glib does exactly that for you in a very portable way (note

								also that glib is the slowest event library known to man).


								There is no supported compilation method available on windows except

								embedding it into other applications.


								Sensible signal handling is officially unsupported by Microsoft - libev

								tries its best, but under most conditions, signals will simply not work.


								Not a libev limitation but worth mentioning: windows apparently doesn't

								accept large writes: instead of resulting in a partial write, windows will

								either accept everything or return C<ENOBUFS> if the buffer is too large,

								so make sure you only write small amounts into your sockets (less than a

								megabyte seems safe, but this apparently depends on the amount of memory

								available).


								Due to the many, low, and arbitrary limits on the win32 platform and

								the abysmal performance of winsockets, using a large number of sockets

								is not recommended (and not reasonable). If your program needs to use

								more than a hundred or so sockets, then likely it needs to use a totally

								different implementation for windows, as libev offers the POSIX readiness

								notification model, which cannot be implemented efficiently on windows

								(due to Microsoft monopoly games).


								A typical way to use libev under windows is to embed it (see the embedding

								section for details) and use the following F<evwrap.h> header file instead

								of F<ev.h>:


								   #define EV_STANDALONE              /* keeps ev from requiring config.h */

								   #define EV_SELECT_IS_WINSOCKET 1   /* configure libev for windows select */


								   #include "ev.h"


								And compile the following F<evwrap.c> file into your project (make sure

								you do I<not> compile the F<ev.c> or any other embedded source files!):


								   #include "evwrap.h"

								   #include "ev.c"


								=head3 The winsocket C<select> function


								The winsocket C<select> function doesn't follow POSIX in that it

								requires socket I<handles> and not socket I<file descriptors> (it is

								also extremely buggy). This makes select very inefficient, and also

								requires a mapping from file descriptors to socket handles (the Microsoft

								C runtime provides the function C<_open_osfhandle> for this). See the

								discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and

								C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.


								The configuration for a "naked" win32 using the Microsoft runtime

								libraries and raw winsocket select is:


								   #define EV_USE_SELECT 1

								   #define EV_SELECT_IS_WINSOCKET 1   /* forces EV_SELECT_USE_FD_SET, too */


								Note that winsockets handling of fd sets is O(n), so you can easily get a

								complexity in the O(n²) range when using win32.


								=head3 Limited number of file descriptors


								Windows has numerous arbitrary (and low) limits on things.


								Early versions of winsocket's select only supported waiting for a maximum

								of C<64> handles (probably owning to the fact that all windows kernels

								can only wait for C<64> things at the same time internally; Microsoft

								recommends spawning a chain of threads and wait for 63 handles and the

								previous thread in each. Sounds great!).


								Newer versions support more handles, but you need to define C<FD_SETSIZE>

								to some high number (e.g. C<2048>) before compiling the winsocket select

								call (which might be in libev or elsewhere, for example, perl and many

								other interpreters do their own select emulation on windows).


								Another limit is the number of file descriptors in the Microsoft runtime

								libraries, which by default is C<64> (there must be a hidden I<64>

								fetish or something like this inside Microsoft). You can increase this

								by calling C<_setmaxstdio>, which can increase this limit to C<2048>

								(another arbitrary limit), but is broken in many versions of the Microsoft

								runtime libraries. This might get you to about C<512> or C<2048> sockets

								(depending on windows version and/or the phase of the moon). To get more,

								you need to wrap all I/O functions and provide your own fd management, but

								the cost of calling select (O(n²)) will likely make this unworkable.


								=head2 PORTABILITY REQUIREMENTS


								In addition to a working ISO-C implementation and of course the

								backend-specific APIs, libev relies on a few additional extensions:


								=over 4


								=item C<void (*)(ev_watcher_type *, int revents)> must have compatible

								calling conventions regardless of C<ev_watcher_type *>.


								Libev assumes not only that all watcher pointers have the same internal

								structure (guaranteed by POSIX but not by ISO C for example), but it also

								assumes that the same (machine) code can be used to call any watcher

								callback: The watcher callbacks have different type signatures, but libev

								calls them using an C<ev_watcher *> internally.


								=item pointer accesses must be thread-atomic


								Accessing a pointer value must be atomic, it must both be readable and

								writable in one piece - this is the case on all current architectures.


								=item C<sig_atomic_t volatile> must be thread-atomic as well


								The type C<sig_atomic_t volatile> (or whatever is defined as

								C<EV_ATOMIC_T>) must be atomic with respect to accesses from different

								threads. This is not part of the specification for C<sig_atomic_t>, but is

								believed to be sufficiently portable.


								=item C<sigprocmask> must work in a threaded environment


								Libev uses C<sigprocmask> to temporarily block signals. This is not

								allowed in a threaded program (C<pthread_sigmask> has to be used). Typical

								pthread implementations will either allow C<sigprocmask> in the "main

								thread" or will block signals process-wide, both behaviours would

								be compatible with libev. Interaction between C<sigprocmask> and

								C<pthread_sigmask> could complicate things, however.


								The most portable way to handle signals is to block signals in all threads

								except the initial one, and run the default loop in the initial thread as

								well.


								=item C<long> must be large enough for common memory allocation sizes


								To improve portability and simplify its API, libev uses C<long> internally

								instead of C<size_t> when allocating its data structures. On non-POSIX

								systems (Microsoft...) this might be unexpectedly low, but is still at

								least 31 bits everywhere, which is enough for hundreds of millions of

								watchers.


								=item C<double> must hold a time value in seconds with enough accuracy


								The type C<double> is used to represent timestamps. It is required to

								have at least 51 bits of mantissa (and 9 bits of exponent), which is

								good enough for at least into the year 4000 with millisecond accuracy

								(the design goal for libev). This requirement is overfulfilled by

								implementations using IEEE 754, which is basically all existing ones. With

								IEEE 754 doubles, you get microsecond accuracy until at least 2200.


								=back


								If you know of other additional requirements drop me a note.


								=head1 ALGORITHMIC COMPLEXITIES


								In this section the complexities of (many of) the algorithms used inside

								libev will be documented. For complexity discussions about backends see

								the documentation for C<ev_default_init>.


								All of the following are about amortised time: If an array needs to be

								extended, libev needs to realloc and move the whole array, but this

								happens asymptotically rarer with higher number of elements, so O(1) might

								mean that libev does a lengthy realloc operation in rare cases, but on

								average it is much faster and asymptotically approaches constant time.


								=over 4


								=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)


								This means that, when you have a watcher that triggers in one hour and

								there are 100 watchers that would trigger before that, then inserting will

								have to skip roughly seven (C<ld 100>) of these watchers.


								=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)


								That means that changing a timer costs less than removing/adding them,

								as only the relative motion in the event queue has to be paid for.


								=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)


								These just add the watcher into an array or at the head of a list.


								=item Stopping check/prepare/idle/fork/async watchers: O(1)


								=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))


								These watchers are stored in lists, so they need to be walked to find the

								correct watcher to remove. The lists are usually short (you don't usually

								have many watchers waiting for the same fd or signal: one is typical, two

								is rare).


								=item Finding the next timer in each loop iteration: O(1)


								By virtue of using a binary or 4-heap, the next timer is always found at a

								fixed position in the storage array.


								=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)


								A change means an I/O watcher gets started or stopped, which requires

								libev to recalculate its status (and possibly tell the kernel, depending

								on backend and whether C<ev_io_set> was used).


								=item Activating one watcher (putting it into the pending state): O(1)


								=item Priority handling: O(number_of_priorities)


								Priorities are implemented by allocating some space for each

								priority. When doing priority-based operations, libev usually has to

								linearly search all the priorities, but starting/stopping and activating

								watchers becomes O(1) with respect to priority handling.


								=item Sending an ev_async: O(1)


								=item Processing ev_async_send: O(number_of_async_watchers)


								=item Processing signals: O(max_signal_number)


								Sending involves a system call I<iff> there were no other C<ev_async_send>

								calls in the current loop iteration. Checking for async and signal events

								involves iterating over all running async watchers or all signal numbers.


								=back


								=head1 PORTING FROM LIBEV 3.X TO 4.X


								The major version 4 introduced some incompatible changes to the API.


								At the moment, the C<ev.h> header file provides compatibility definitions

								for all changes, so most programs should still compile. The compatibility

								layer might be removed in later versions of libev, so better update to the

								new API early than late.


								=over 4


								=item C<EV_COMPAT3> backwards compatibility mechanism


								The backward compatibility mechanism can be controlled by

								C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>

								section.


								=item C<ev_default_destroy> and C<ev_default_fork> have been removed


								These calls can be replaced easily by their C<ev_loop_xxx> counterparts:


								   ev_loop_destroy (EV_DEFAULT_UC);

								   ev_loop_fork (EV_DEFAULT);


								=item function/symbol renames


								A number of functions and symbols have been renamed:


								  ev_loop         => ev_run

								  EVLOOP_NONBLOCK => EVRUN_NOWAIT

								  EVLOOP_ONESHOT  => EVRUN_ONCE


								  ev_unloop       => ev_break

								  EVUNLOOP_CANCEL => EVBREAK_CANCEL

								  EVUNLOOP_ONE    => EVBREAK_ONE

								  EVUNLOOP_ALL    => EVBREAK_ALL


								  EV_TIMEOUT      => EV_TIMER


								  ev_loop_count   => ev_iteration

								  ev_loop_depth   => ev_depth

								  ev_loop_verify  => ev_verify


								Most functions working on C<struct ev_loop> objects don't have an

								C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and

								associated constants have been renamed to not collide with the C<struct

								ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme

								as all other watcher types. Note that C<ev_loop_fork> is still called

								C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>

								typedef.


								=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>


								The preprocessor symbol C<EV_MINIMAL> has been replaced by a different

								mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile

								and work, but the library code will of course be larger.


								=back


								=head1 GLOSSARY


								=over 4


								=item active


								A watcher is active as long as it has been started and not yet stopped.

								See L<WATCHER STATES> for details.


								=item application


								In this document, an application is whatever is using libev.


								=item backend


								The part of the code dealing with the operating system interfaces.


								=item callback


								The address of a function that is called when some event has been

								detected. Callbacks are being passed the event loop, the watcher that

								received the event, and the actual event bitset.


								=item callback/watcher invocation


								The act of calling the callback associated with a watcher.


								=item event


								A change of state of some external event, such as data now being available

								for reading on a file descriptor, time having passed or simply not having

								any other events happening anymore.


								In libev, events are represented as single bits (such as C<EV_READ> or

								C<EV_TIMER>).


								=item event library


								A software package implementing an event model and loop.


								=item event loop


								An entity that handles and processes external events and converts them

								into callback invocations.


								=item event model


								The model used to describe how an event loop handles and processes

								watchers and events.


								=item pending


								A watcher is pending as soon as the corresponding event has been

								detected. See L<WATCHER STATES> for details.


								=item real time


								The physical time that is observed. It is apparently strictly monotonic :)


								=item wall-clock time


								The time and date as shown on clocks. Unlike real time, it can actually

								be wrong and jump forwards and backwards, e.g. when you adjust your

								clock.


								=item watcher


								A data structure that describes interest in certain events. Watchers need

								to be started (attached to an event loop) before they can receive events.


								=back


								=head1 AUTHOR


								Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael

								Magnusson and Emanuele Giaquinta, and minor corrections by many others.