rtc_base/event.cc

/*
 *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "rtc_base/event.h"

#if defined(WEBRTC_WIN)
#include <windows.h>
#elif defined(WEBRTC_POSIX)
#include <errno.h>
#include <pthread.h>
#include <sys/time.h>
#include <time.h>
#else
#error "Must define either WEBRTC_WIN or WEBRTC_POSIX."
#endif

#include "rtc_base/checks.h"
#include "rtc_base/synchronization/yield_policy.h"
#include "rtc_base/system/warn_current_thread_is_deadlocked.h"

namespace rtc {

Event::Event() : Event(false, false) {}

#if defined(WEBRTC_WIN)

Event::Event(bool manual_reset, bool initially_signaled) {
  event_handle_ = ::CreateEvent(nullptr,  // Security attributes.
                                manual_reset, initially_signaled,
                                nullptr);  // Name.
  RTC_CHECK(event_handle_);
}

Event::~Event() {
  CloseHandle(event_handle_);
}

void Event::Set() {
  SetEvent(event_handle_);
}

void Event::Reset() {
  ResetEvent(event_handle_);
}

bool Event::Wait(int milliseconds) {
  ScopedYieldPolicy::YieldExecution();
  DWORD ms = (milliseconds == kForever) ? INFINITE : milliseconds;
  return (WaitForSingleObject(event_handle_, ms) == WAIT_OBJECT_0);
}

#elif defined(WEBRTC_POSIX)

// On MacOS, clock_gettime is available from version 10.12, and on
// iOS, from version 10.0. So we can't use it yet.
#if defined(WEBRTC_MAC) || defined(WEBRTC_IOS)
#define USE_CLOCK_GETTIME 0
#define USE_PTHREAD_COND_TIMEDWAIT_MONOTONIC_NP 0
// On Android, pthread_condattr_setclock is available from version 21. By
// default, we target a new enough version for 64-bit platforms but not for
// 32-bit platforms. For older versions, use
// pthread_cond_timedwait_monotonic_np.
#elif defined(WEBRTC_ANDROID) && (__ANDROID_API__ < 21)
#define USE_CLOCK_GETTIME 1
#define USE_PTHREAD_COND_TIMEDWAIT_MONOTONIC_NP 1
#else
#define USE_CLOCK_GETTIME 1
#define USE_PTHREAD_COND_TIMEDWAIT_MONOTONIC_NP 0
#endif

Event::Event(bool manual_reset, bool initially_signaled)
    : is_manual_reset_(manual_reset), event_status_(initially_signaled) {
  RTC_CHECK(pthread_mutex_init(&event_mutex_, nullptr) == 0);
  pthread_condattr_t cond_attr;
  RTC_CHECK(pthread_condattr_init(&cond_attr) == 0);
#if USE_CLOCK_GETTIME && !USE_PTHREAD_COND_TIMEDWAIT_MONOTONIC_NP
  RTC_CHECK(pthread_condattr_setclock(&cond_attr, CLOCK_MONOTONIC) == 0);
#endif
  RTC_CHECK(pthread_cond_init(&event_cond_, &cond_attr) == 0);
  pthread_condattr_destroy(&cond_attr);
}

Event::~Event() {
  pthread_mutex_destroy(&event_mutex_);
  pthread_cond_destroy(&event_cond_);
}

void Event::Set() {
  pthread_mutex_lock(&event_mutex_);
  event_status_ = true;
  pthread_cond_broadcast(&event_cond_);
  pthread_mutex_unlock(&event_mutex_);
}

void Event::Reset() {
  pthread_mutex_lock(&event_mutex_);
  event_status_ = false;
  pthread_mutex_unlock(&event_mutex_);
}

namespace {

timespec GetTimespec(const int milliseconds_from_now) {
  timespec ts;

  // Get the current time.
#if USE_CLOCK_GETTIME
  clock_gettime(CLOCK_MONOTONIC, &ts);
#else
  timeval tv;
  gettimeofday(&tv, nullptr);
  ts.tv_sec = tv.tv_sec;
  ts.tv_nsec = tv.tv_usec * 1000;
#endif

  // Add the specified number of milliseconds to it.
  ts.tv_sec += (milliseconds_from_now / 1000);
  ts.tv_nsec += (milliseconds_from_now % 1000) * 1000000;

  // Normalize.
  if (ts.tv_nsec >= 1000000000) {
    ts.tv_sec++;
    ts.tv_nsec -= 1000000000;
  }

  return ts;
}

}  // namespace

bool Event::Wait(const int milliseconds) {
  // Set a timeout for the given number of milliseconds, or 3000 ms if the
  // caller asked for kForever.
  const timespec ts =
      GetTimespec(milliseconds == kForever ? 3000 : milliseconds);

  ScopedYieldPolicy::YieldExecution();
  pthread_mutex_lock(&event_mutex_);

  // Wait for the event to trigger or the timeout to expire, whichever comes
  // first.
  int error = 0;
  while (!event_status_ && error == 0) {
#if USE_PTHREAD_COND_TIMEDWAIT_MONOTONIC_NP
    error =
        pthread_cond_timedwait_monotonic_np(&event_cond_, &event_mutex_, &ts);
#else
    error = pthread_cond_timedwait(&event_cond_, &event_mutex_, &ts);
#endif
  }

  if (milliseconds == kForever && error == ETIMEDOUT) {
    // Our 3000 ms timeout expired, but the caller asked us to wait forever, so
    // do that.
    webrtc::WarnThatTheCurrentThreadIsProbablyDeadlocked();
    error = 0;
    while (!event_status_ && error == 0) {
      error = pthread_cond_wait(&event_cond_, &event_mutex_);
    }
  }

  // NOTE(liulk): Exactly one thread will auto-reset this event. All
  // the other threads will think it's unsignaled.  This seems to be
  // consistent with auto-reset events in WEBRTC_WIN
  if (error == 0 && !is_manual_reset_)
    event_status_ = false;

  pthread_mutex_unlock(&event_mutex_);

  return (error == 0);
}

#endif

}  // namespace rtc