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/*
* 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.
const int current_access_count = access_count_;
access_count_ = access_count_ + 1;
if (current_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_ = access_count_ - 1;
}
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
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