1 /* 2 * Copyright (c) 2016 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #include "rtc_base/race_checker.h" 12 13 namespace rtc { 14 RaceChecker()15RaceChecker::RaceChecker() {} 16 17 // Note that the implementation here is in itself racy, but we pretend it does 18 // not matter because we want this useful in release builds without having to 19 // pay the cost of using atomics. A race hitting the race checker is likely to 20 // cause access_count_ to diverge from zero and therefore cause the ThreadRef 21 // comparison to fail, signaling a race, although it may not be in the exact 22 // spot where a race *first* appeared in the code we're trying to protect. There 23 // is also a chance that an actual race is missed, however the probability of 24 // that has been considered small enough to be an acceptable trade off. Acquire() const25bool RaceChecker::Acquire() const { 26 const PlatformThreadRef current_thread = CurrentThreadRef(); 27 // Set new accessing thread if this is a new use. 28 const int current_access_count = access_count_; 29 access_count_ = access_count_ + 1; 30 if (current_access_count == 0) 31 accessing_thread_ = current_thread; 32 // If this is being used concurrently this check will fail for the second 33 // thread entering since it won't set the thread. Recursive use of checked 34 // methods are OK since the accessing thread remains the same. 35 const PlatformThreadRef accessing_thread = accessing_thread_; 36 return IsThreadRefEqual(accessing_thread, current_thread); 37 } 38 Release() const39void RaceChecker::Release() const { 40 access_count_ = access_count_ - 1; 41 } 42 43 namespace internal { RaceCheckerScope(const RaceChecker * race_checker)44RaceCheckerScope::RaceCheckerScope(const RaceChecker* race_checker) 45 : race_checker_(race_checker), race_check_ok_(race_checker->Acquire()) {} 46 RaceDetected() const47bool RaceCheckerScope::RaceDetected() const { 48 return !race_check_ok_; 49 } 50 ~RaceCheckerScope()51RaceCheckerScope::~RaceCheckerScope() { 52 race_checker_->Release(); 53 } 54 55 } // namespace internal 56 } // namespace rtc 57