Master was disconnecting its workers as soon as they both started up.
Meanwhile, the workers were trying to listen. Its a race, sometimes the
disconnect would happen between when worker gets the response message,
and acks that message with a 'listening'. This worked OK after v0.11
introduced a behaviour where disconnect would always exit the worker,
but once that backwards-incompatible behaviour is removed, the worker
lives long enough to try and respond to the master, and child_process
errors at the attempt to send from a disconnected child.
Commit 30e5366b ("core: Use a uv_signal for debug listener") changed
SIGUSR1 handling from a signal handler to libuv's uv_signal_*()
functionality to fix a race condition (and possible hang) in the
signal handler.
While a good change in itself, it made it impossible to interrupt
long running scripts. When a script is stuck in a busy loop, control
never returns to the event loop, which in turn means the signal
callback - and therefore the debugger - is never invoked.
This commit changes SIGUSR1 handling back to a normal signal handler
but one that treads _very_ carefully.
Implement support for debugging cluster workers. Each worker process
is assigned a new debug port in an increasing sequence.
I.e. when master process uses port 5858, then worker 1 uses port 5859,
worker 2 uses port 5860, and so on.
Introduce new command-line parameter '--debug-port=' which sets debug_port
but does not start debugger. This option works for all node processes, it
is not specific to cluster workers.
Fixesjoyent/node#5318.