node/deps/v8/src/platform-openbsd.cc

// Copyright 2006-2011 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
//       copyright notice, this list of conditions and the following
//       disclaimer in the documentation and/or other materials provided
//       with the distribution.
//     * Neither the name of Google Inc. nor the names of its
//       contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// Platform specific code for OpenBSD goes here. For the POSIX comaptible parts
// the implementation is in platform-posix.cc.

#include <pthread.h>
#include <semaphore.h>
#include <signal.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/types.h>
#include <stdlib.h>

#include <sys/types.h>  // mmap & munmap
#include <sys/mman.h>   // mmap & munmap
#include <sys/stat.h>   // open
#include <sys/fcntl.h>  // open
#include <unistd.h>     // getpagesize
#include <execinfo.h>   // backtrace, backtrace_symbols
#include <strings.h>    // index
#include <errno.h>
#include <stdarg.h>
#include <limits.h>

#undef MAP_TYPE

#include "v8.h"
#include "v8threads.h"

#include "platform.h"
#include "vm-state-inl.h"


namespace v8 {
namespace internal {

// 0 is never a valid thread id on OpenBSD since tids and pids share a
// name space and pid 0 is used to kill the group (see man 2 kill).
static const pthread_t kNoThread = (pthread_t) 0;


double ceiling(double x) {
    // Correct as on OS X
    if (-1.0 < x && x < 0.0) {
        return -0.0;
    } else {
        return ceil(x);
    }
}


static Mutex* limit_mutex = NULL;


void OS::Setup() {
  // Seed the random number generator.
  // Convert the current time to a 64-bit integer first, before converting it
  // to an unsigned. Going directly can cause an overflow and the seed to be
  // set to all ones. The seed will be identical for different instances that
  // call this setup code within the same millisecond.
  uint64_t seed = static_cast<uint64_t>(TimeCurrentMillis());
  srandom(static_cast<unsigned int>(seed));
  limit_mutex = CreateMutex();
}


void OS::ReleaseStore(volatile AtomicWord* ptr, AtomicWord value) {
  __asm__ __volatile__("" : : : "memory");
  *ptr = value;
}


uint64_t OS::CpuFeaturesImpliedByPlatform() {
  return 0;  // OpenBSD runs on anything.
}


int OS::ActivationFrameAlignment() {
  // 16 byte alignment on OpenBSD
  return 16;
}


const char* OS::LocalTimezone(double time) {
  if (isnan(time)) return "";
  time_t tv = static_cast<time_t>(floor(time/msPerSecond));
  struct tm* t = localtime(&tv);
  if (NULL == t) return "";
  return t->tm_zone;
}


double OS::LocalTimeOffset() {
  time_t tv = time(NULL);
  struct tm* t = localtime(&tv);
  // tm_gmtoff includes any daylight savings offset, so subtract it.
  return static_cast<double>(t->tm_gmtoff * msPerSecond -
                             (t->tm_isdst > 0 ? 3600 * msPerSecond : 0));
}


// We keep the lowest and highest addresses mapped as a quick way of
// determining that pointers are outside the heap (used mostly in assertions
// and verification).  The estimate is conservative, ie, not all addresses in
// 'allocated' space are actually allocated to our heap.  The range is
// [lowest, highest), inclusive on the low and and exclusive on the high end.
static void* lowest_ever_allocated = reinterpret_cast<void*>(-1);
static void* highest_ever_allocated = reinterpret_cast<void*>(0);


static void UpdateAllocatedSpaceLimits(void* address, int size) {
  ASSERT(limit_mutex != NULL);
  ScopedLock lock(limit_mutex);

  lowest_ever_allocated = Min(lowest_ever_allocated, address);
  highest_ever_allocated =
      Max(highest_ever_allocated,
          reinterpret_cast<void*>(reinterpret_cast<char*>(address) + size));
}


bool OS::IsOutsideAllocatedSpace(void* address) {
  return address < lowest_ever_allocated || address >= highest_ever_allocated;
}


size_t OS::AllocateAlignment() {
  return getpagesize();
}


void* OS::Allocate(const size_t requested,
                   size_t* allocated,
                   bool executable) {
  const size_t msize = RoundUp(requested, getpagesize());
  int prot = PROT_READ | PROT_WRITE | (executable ? PROT_EXEC : 0);
  void* mbase = mmap(NULL, msize, prot, MAP_PRIVATE | MAP_ANON, -1, 0);

  if (mbase == MAP_FAILED) {
    LOG(ISOLATE, StringEvent("OS::Allocate", "mmap failed"));
    return NULL;
  }
  *allocated = msize;
  UpdateAllocatedSpaceLimits(mbase, msize);
  return mbase;
}


void OS::Free(void* buf, const size_t length) {
  // TODO(1240712): munmap has a return value which is ignored here.
  int result = munmap(buf, length);
  USE(result);
  ASSERT(result == 0);
}


void OS::Sleep(int milliseconds) {
  unsigned int ms = static_cast<unsigned int>(milliseconds);
  usleep(1000 * ms);
}


void OS::Abort() {
  // Redirect to std abort to signal abnormal program termination.
  abort();
}


void OS::DebugBreak() {
#if (defined(__arm__) || defined(__thumb__))
# if defined(CAN_USE_ARMV5_INSTRUCTIONS)
  asm("bkpt 0");
# endif
#else
  asm("int $3");
#endif
}


class PosixMemoryMappedFile : public OS::MemoryMappedFile {
 public:
  PosixMemoryMappedFile(FILE* file, void* memory, int size)
    : file_(file), memory_(memory), size_(size) { }
  virtual ~PosixMemoryMappedFile();
  virtual void* memory() { return memory_; }
  virtual int size() { return size_; }
 private:
  FILE* file_;
  void* memory_;
  int size_;
};


OS::MemoryMappedFile* OS::MemoryMappedFile::open(const char* name) {
  FILE* file = fopen(name, "r+");
  if (file == NULL) return NULL;

  fseek(file, 0, SEEK_END);
  int size = ftell(file);

  void* memory =
      mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fileno(file), 0);
  return new PosixMemoryMappedFile(file, memory, size);
}


OS::MemoryMappedFile* OS::MemoryMappedFile::create(const char* name, int size,
    void* initial) {
  FILE* file = fopen(name, "w+");
  if (file == NULL) return NULL;
  int result = fwrite(initial, size, 1, file);
  if (result < 1) {
    fclose(file);
    return NULL;
  }
  void* memory =
      mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fileno(file), 0);
  return new PosixMemoryMappedFile(file, memory, size);
}


PosixMemoryMappedFile::~PosixMemoryMappedFile() {
  if (memory_) OS::Free(memory_, size_);
  fclose(file_);
}


static unsigned StringToLong(char* buffer) {
  return static_cast<unsigned>(strtol(buffer, NULL, 16));  // NOLINT
}


void OS::LogSharedLibraryAddresses() {
  static const int MAP_LENGTH = 1024;
  int fd = open("/proc/self/maps", O_RDONLY);
  if (fd < 0) return;
  while (true) {
    char addr_buffer[11];
    addr_buffer[0] = '0';
    addr_buffer[1] = 'x';
    addr_buffer[10] = 0;
    int result = read(fd, addr_buffer + 2, 8);
    if (result < 8) break;
    unsigned start = StringToLong(addr_buffer);
    result = read(fd, addr_buffer + 2, 1);
    if (result < 1) break;
    if (addr_buffer[2] != '-') break;
    result = read(fd, addr_buffer + 2, 8);
    if (result < 8) break;
    unsigned end = StringToLong(addr_buffer);
    char buffer[MAP_LENGTH];
    int bytes_read = -1;
    do {
      bytes_read++;
      if (bytes_read >= MAP_LENGTH - 1)
        break;
      result = read(fd, buffer + bytes_read, 1);
      if (result < 1) break;
    } while (buffer[bytes_read] != '\n');
    buffer[bytes_read] = 0;
    // Ignore mappings that are not executable.
    if (buffer[3] != 'x') continue;
    char* start_of_path = index(buffer, '/');
    // There may be no filename in this line.  Skip to next.
    if (start_of_path == NULL) continue;
    buffer[bytes_read] = 0;
    LOG(i::Isolate::Current(), SharedLibraryEvent(start_of_path, start, end));
  }
  close(fd);
}


void OS::SignalCodeMovingGC() {
}


int OS::StackWalk(Vector<OS::StackFrame> frames) {
  int frames_size = frames.length();
  ScopedVector<void*> addresses(frames_size);

  int frames_count = backtrace(addresses.start(), frames_size);

  char** symbols = backtrace_symbols(addresses.start(), frames_count);
  if (symbols == NULL) {
    return kStackWalkError;
  }

  for (int i = 0; i < frames_count; i++) {
    frames[i].address = addresses[i];
    // Format a text representation of the frame based on the information
    // available.
    SNPrintF(MutableCStrVector(frames[i].text, kStackWalkMaxTextLen),
             "%s",
             symbols[i]);
    // Make sure line termination is in place.
    frames[i].text[kStackWalkMaxTextLen - 1] = '\0';
  }

  free(symbols);

  return frames_count;
}


// Constants used for mmap.
static const int kMmapFd = -1;
static const int kMmapFdOffset = 0;


VirtualMemory::VirtualMemory(size_t size) {
  address_ = mmap(NULL, size, PROT_NONE,
                  MAP_PRIVATE | MAP_ANON | MAP_NORESERVE,
                  kMmapFd, kMmapFdOffset);
  size_ = size;
}


VirtualMemory::~VirtualMemory() {
  if (IsReserved()) {
    OS::Free(address(), size());
    address_ = MAP_FAILED
  }
}


bool VirtualMemory::IsReserved() {
  return address_ != MAP_FAILED;
}


bool VirtualMemory::Commit(void* address, size_t size, bool executable) {
  int prot = PROT_READ | PROT_WRITE | (executable ? PROT_EXEC : 0);
  if (MAP_FAILED == mmap(address, size, prot,
                         MAP_PRIVATE | MAP_ANON | MAP_FIXED,
                         kMmapFd, kMmapFdOffset)) {
    return false;
  }

  UpdateAllocatedSpaceLimits(address, size);
  return true;
}


bool VirtualMemory::Uncommit(void* address, size_t size) {
  return mmap(address, size, PROT_NONE,
              MAP_PRIVATE | MAP_ANON | MAP_NORESERVE | MAP_FIXED,
              kMmapFd, kMmapFdOffset) != MAP_FAILED;
}


class Thread::PlatformData : public Malloced {
 public:
  pthread_t thread_;  // Thread handle for pthread.
};


Thread::Thread(const Options& options)
    : data_(new PlatformData),
      stack_size_(options.stack_size) {
  set_name(options.name);
}


Thread::Thread(const char* name)
    : data_(new PlatformData),
      stack_size_(0) {
  set_name(name);
}


Thread::~Thread() {
  delete data_;
}


static void* ThreadEntry(void* arg) {
  Thread* thread = reinterpret_cast<Thread*>(arg);
  // This is also initialized by the first argument to pthread_create() but we
  // don't know which thread will run first (the original thread or the new
  // one) so we initialize it here too.
  thread->data()->thread_ = pthread_self();
  ASSERT(thread->data()->thread_ != kNoThread);
  thread->Run();
  return NULL;
}


void Thread::set_name(const char* name) {
  strncpy(name_, name, sizeof(name_));
  name_[sizeof(name_) - 1] = '\0';
}


void Thread::Start() {
  pthread_attr_t* attr_ptr = NULL;
  pthread_attr_t attr;
  if (stack_size_ > 0) {
    pthread_attr_init(&attr);
    pthread_attr_setstacksize(&attr, static_cast<size_t>(stack_size_));
    attr_ptr = &attr;
  }
  pthread_create(&data_->thread_, attr_ptr, ThreadEntry, this);
  ASSERT(data_->thread_ != kNoThread);
}


void Thread::Join() {
  pthread_join(data_->thread_, NULL);
}


Thread::LocalStorageKey Thread::CreateThreadLocalKey() {
  pthread_key_t key;
  int result = pthread_key_create(&key, NULL);
  USE(result);
  ASSERT(result == 0);
  return static_cast<LocalStorageKey>(key);
}


void Thread::DeleteThreadLocalKey(LocalStorageKey key) {
  pthread_key_t pthread_key = static_cast<pthread_key_t>(key);
  int result = pthread_key_delete(pthread_key);
  USE(result);
  ASSERT(result == 0);
}


void* Thread::GetThreadLocal(LocalStorageKey key) {
  pthread_key_t pthread_key = static_cast<pthread_key_t>(key);
  return pthread_getspecific(pthread_key);
}


void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
  pthread_key_t pthread_key = static_cast<pthread_key_t>(key);
  pthread_setspecific(pthread_key, value);
}


void Thread::YieldCPU() {
  sched_yield();
}


class OpenBSDMutex : public Mutex {
 public:
  OpenBSDMutex() {
    pthread_mutexattr_t attrs;
    int result = pthread_mutexattr_init(&attrs);
    ASSERT(result == 0);
    result = pthread_mutexattr_settype(&attrs, PTHREAD_MUTEX_RECURSIVE);
    ASSERT(result == 0);
    result = pthread_mutex_init(&mutex_, &attrs);
    ASSERT(result == 0);
  }

  virtual ~OpenBSDMutex() { pthread_mutex_destroy(&mutex_); }

  virtual int Lock() {
    int result = pthread_mutex_lock(&mutex_);
    return result;
  }

  virtual int Unlock() {
    int result = pthread_mutex_unlock(&mutex_);
    return result;
  }

  virtual bool TryLock() {
    int result = pthread_mutex_trylock(&mutex_);
    // Return false if the lock is busy and locking failed.
    if (result == EBUSY) {
      return false;
    }
    ASSERT(result == 0);  // Verify no other errors.
    return true;
  }

 private:
  pthread_mutex_t mutex_;   // Pthread mutex for POSIX platforms.
};


Mutex* OS::CreateMutex() {
  return new OpenBSDMutex();
}


class OpenBSDSemaphore : public Semaphore {
 public:
  explicit OpenBSDSemaphore(int count) {  sem_init(&sem_, 0, count); }
  virtual ~OpenBSDSemaphore() { sem_destroy(&sem_); }

  virtual void Wait();
  virtual bool Wait(int timeout);
  virtual void Signal() { sem_post(&sem_); }
 private:
  sem_t sem_;
};


void OpenBSDSemaphore::Wait() {
  while (true) {
    int result = sem_wait(&sem_);
    if (result == 0) return;  // Successfully got semaphore.
    CHECK(result == -1 && errno == EINTR);  // Signal caused spurious wakeup.
  }
}


bool OpenBSDSemaphore::Wait(int timeout) {
  const long kOneSecondMicros = 1000000;  // NOLINT

  // Split timeout into second and nanosecond parts.
  struct timeval delta;
  delta.tv_usec = timeout % kOneSecondMicros;
  delta.tv_sec = timeout / kOneSecondMicros;

  struct timeval current_time;
  // Get the current time.
  if (gettimeofday(&current_time, NULL) == -1) {
    return false;
  }

  // Calculate time for end of timeout.
  struct timeval end_time;
  timeradd(&current_time, &delta, &end_time);

  struct timespec ts;
  TIMEVAL_TO_TIMESPEC(&end_time, &ts);

  int to = ts.tv_sec;

  while (true) {
    int result = sem_trywait(&sem_);
    if (result == 0) return true;  // Successfully got semaphore.
    if (!to) return false;  // Timeout.
    CHECK(result == -1 && errno == EINTR);  // Signal caused spurious wakeup.
    usleep(ts.tv_nsec / 1000);
    to--;
  }
}


Semaphore* OS::CreateSemaphore(int count) {
  return new OpenBSDSemaphore(count);
}


static pthread_t GetThreadID() {
  pthread_t thread_id = pthread_self();
  return thread_id;
}


class Sampler::PlatformData : public Malloced {
 public:
  PlatformData() : vm_tid_(GetThreadID()) {}

  pthread_t vm_tid() const { return vm_tid_; }

 private:
  pthread_t vm_tid_;
};


static void ProfilerSignalHandler(int signal, siginfo_t* info, void* context) {
  USE(info);
  if (signal != SIGPROF) return;
  Isolate* isolate = Isolate::UncheckedCurrent();
  if (isolate == NULL || !isolate->IsInitialized() || !isolate->IsInUse()) {
    // We require a fully initialized and entered isolate.
    return;
  }
  if (v8::Locker::IsActive() &&
      !isolate->thread_manager()->IsLockedByCurrentThread()) {
    return;
  }

  Sampler* sampler = isolate->logger()->sampler();
  if (sampler == NULL || !sampler->IsActive()) return;

  TickSample sample_obj;
  TickSample* sample = CpuProfiler::TickSampleEvent(isolate);
  if (sample == NULL) sample = &sample_obj;

  // Extracting the sample from the context is extremely machine dependent.
  ucontext_t* ucontext = reinterpret_cast<ucontext_t*>(context);
  sample->state = isolate->current_vm_state();
#if V8_HOST_ARCH_IA32
  sample->pc = reinterpret_cast<Address>(ucontext->sc_eip);
  sample->sp = reinterpret_cast<Address>(ucontext->sc_esp);
  sample->fp = reinterpret_cast<Address>(ucontext->sc_ebp);
#elif V8_HOST_ARCH_X64
  sample->pc = reinterpret_cast<Address>(ucontext->sc_rip);
  sample->sp = reinterpret_cast<Address>(ucontext->sc_rsp);
  sample->fp = reinterpret_cast<Address>(ucontext->sc_rbp);
#elif V8_HOST_ARCH_ARM
  sample->pc = reinterpret_cast<Address>(ucontext->sc_r15);
  sample->sp = reinterpret_cast<Address>(ucontext->sc_r13);
  sample->fp = reinterpret_cast<Address>(ucontext->sc_r11);
#endif
  sampler->SampleStack(sample);
  sampler->Tick(sample);
}


class SignalSender : public Thread {
 public:
  enum SleepInterval {
    HALF_INTERVAL,
    FULL_INTERVAL
  };

  explicit SignalSender(int interval)
      : Thread("SignalSender"),
        interval_(interval) {}

  static void AddActiveSampler(Sampler* sampler) {
    ScopedLock lock(mutex_);
    SamplerRegistry::AddActiveSampler(sampler);
    if (instance_ == NULL) {
      // Install a signal handler.
      struct sigaction sa;
      sa.sa_sigaction = ProfilerSignalHandler;
      sigemptyset(&sa.sa_mask);
      sa.sa_flags = SA_RESTART | SA_SIGINFO;
      signal_handler_installed_ =
          (sigaction(SIGPROF, &sa, &old_signal_handler_) == 0);

      // Start a thread that sends SIGPROF signal to VM threads.
      instance_ = new SignalSender(sampler->interval());
      instance_->Start();
    } else {
      ASSERT(instance_->interval_ == sampler->interval());
    }
  }

  static void RemoveActiveSampler(Sampler* sampler) {
    ScopedLock lock(mutex_);
    SamplerRegistry::RemoveActiveSampler(sampler);
    if (SamplerRegistry::GetState() == SamplerRegistry::HAS_NO_SAMPLERS) {
      RuntimeProfiler::StopRuntimeProfilerThreadBeforeShutdown(instance_);
      delete instance_;
      instance_ = NULL;

      // Restore the old signal handler.
      if (signal_handler_installed_) {
        sigaction(SIGPROF, &old_signal_handler_, 0);
        signal_handler_installed_ = false;
      }
    }
  }

  // Implement Thread::Run().
  virtual void Run() {
    SamplerRegistry::State state;
    while ((state = SamplerRegistry::GetState()) !=
           SamplerRegistry::HAS_NO_SAMPLERS) {
      bool cpu_profiling_enabled =
          (state == SamplerRegistry::HAS_CPU_PROFILING_SAMPLERS);
      bool runtime_profiler_enabled = RuntimeProfiler::IsEnabled();
      // When CPU profiling is enabled both JavaScript and C++ code is
      // profiled. We must not suspend.
      if (!cpu_profiling_enabled) {
        if (rate_limiter_.SuspendIfNecessary()) continue;
      }
      if (cpu_profiling_enabled && runtime_profiler_enabled) {
        if (!SamplerRegistry::IterateActiveSamplers(&DoCpuProfile, this)) {
          return;
        }
        Sleep(HALF_INTERVAL);
        if (!SamplerRegistry::IterateActiveSamplers(&DoRuntimeProfile, NULL)) {
          return;
        }
        Sleep(HALF_INTERVAL);
      } else {
        if (cpu_profiling_enabled) {
          if (!SamplerRegistry::IterateActiveSamplers(&DoCpuProfile,
                                                      this)) {
            return;
          }
        }
        if (runtime_profiler_enabled) {
          if (!SamplerRegistry::IterateActiveSamplers(&DoRuntimeProfile,
                                                      NULL)) {
            return;
          }
        }
        Sleep(FULL_INTERVAL);
      }
    }
  }

  static void DoCpuProfile(Sampler* sampler, void* raw_sender) {
    if (!sampler->IsProfiling()) return;
    SignalSender* sender = reinterpret_cast<SignalSender*>(raw_sender);
    sender->SendProfilingSignal(sampler->platform_data()->vm_tid());
  }

  static void DoRuntimeProfile(Sampler* sampler, void* ignored) {
    if (!sampler->isolate()->IsInitialized()) return;
    sampler->isolate()->runtime_profiler()->NotifyTick();
  }

  void SendProfilingSignal(pthread_t tid) {
    if (!signal_handler_installed_) return;
    pthread_kill(tid, SIGPROF);
  }

  void Sleep(SleepInterval full_or_half) {
    // Convert ms to us and subtract 100 us to compensate delays
    // occuring during signal delivery.
    useconds_t interval = interval_ * 1000 - 100;
    if (full_or_half == HALF_INTERVAL) interval /= 2;
    int result = usleep(interval);
#ifdef DEBUG
    if (result != 0 && errno != EINTR) {
      fprintf(stderr,
              "SignalSender usleep error; interval = %u, errno = %d\n",
              interval,
              errno);
      ASSERT(result == 0 || errno == EINTR);
    }
#endif
    USE(result);
  }

  const int interval_;
  RuntimeProfilerRateLimiter rate_limiter_;

  // Protects the process wide state below.
  static Mutex* mutex_;
  static SignalSender* instance_;
  static bool signal_handler_installed_;
  static struct sigaction old_signal_handler_;

  DISALLOW_COPY_AND_ASSIGN(SignalSender);
};

Mutex* SignalSender::mutex_ = OS::CreateMutex();
SignalSender* SignalSender::instance_ = NULL;
struct sigaction SignalSender::old_signal_handler_;
bool SignalSender::signal_handler_installed_ = false;


Sampler::Sampler(Isolate* isolate, int interval)
    : isolate_(isolate),
      interval_(interval),
      profiling_(false),
      active_(false),
      samples_taken_(0) {
  data_ = new PlatformData;
}


Sampler::~Sampler() {
  ASSERT(!IsActive());
  delete data_;
}


void Sampler::Start() {
  ASSERT(!IsActive());
  SetActive(true);
  SignalSender::AddActiveSampler(this);
}


void Sampler::Stop() {
  ASSERT(IsActive());
  SignalSender::RemoveActiveSampler(this);
  SetActive(false);
}


} }  // namespace v8::internal