rtc_base/race_checker.cc

/*
 *  Copyright (c) 2016 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/race_checker.h"

namespace rtc {

RaceChecker::RaceChecker() {}

// Note that the implementation here is in itself racy, but we pretend it does
// not matter because we want this useful in release builds without having to
// pay the cost of using atomics. A race hitting the race checker is likely to
// cause access_count_ to diverge from zero and therefore cause the ThreadRef
// comparison to fail, signaling a race, although it may not be in the exact
// spot where a race *first* appeared in the code we're trying to protect. There
// is also a chance that an actual race is missed, however the probability of
// that has been considered small enough to be an acceptable trade off.
bool RaceChecker::Acquire() const {
  const PlatformThreadRef current_thread = CurrentThreadRef();
  // Set new accessing thread if this is a new use.
  if (access_count_++ == 0)
    accessing_thread_ = current_thread;
  // If this is being used concurrently this check will fail for the second
  // thread entering since it won't set the thread. Recursive use of checked
  // methods are OK since the accessing thread remains the same.
  const PlatformThreadRef accessing_thread = accessing_thread_;
  return IsThreadRefEqual(accessing_thread, current_thread);
}

void RaceChecker::Release() const {
  --access_count_;
}

namespace internal {
RaceCheckerScope::RaceCheckerScope(const RaceChecker* race_checker)
    : race_checker_(race_checker), race_check_ok_(race_checker->Acquire()) {}

bool RaceCheckerScope::RaceDetected() const {
  return !race_check_ok_;
}

RaceCheckerScope::~RaceCheckerScope() {
  race_checker_->Release();
}

}  // namespace internal
}  // namespace rtc