Add a race-checking mechanism.

webrtc/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 "webrtc/base/race_checker.h"
+
+namespace rtc {
+RaceChecker::RaceChecker() {}
+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.
+  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