Add a race-checking mechanism.

webrtc/base/race_checker.h

Index: webrtc/base/race_checker.h
diff --git a/webrtc/base/race_checker.h b/webrtc/base/race_checker.h
new file mode 100644
index 0000000000000000000000000000000000000000..692d6b76668233a6db3910b8622b2e8cf2e15a83
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+++ b/webrtc/base/race_checker.h
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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.
+ */
+
+#ifndef WEBRTC_BASE_RACE_CHECKER_H_
+#define WEBRTC_BASE_RACE_CHECKER_H_
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/platform_thread.h"
+#include "webrtc/base/thread_annotations.h"
+
+namespace rtc {
+
+namespace internal {
+class RaceCheckerScope;
+}  // namespace internal
+
+// Best-effort race-checking implementation. This primitive uses no
+// synchronization at all to be as-fast-as-possible in the non-racy case.
+class LOCKABLE RaceChecker {
+ public:
+  friend class internal::RaceCheckerScope;
+  RaceChecker();
+
+ private:
+  bool Acquire() const EXCLUSIVE_LOCK_FUNCTION();
+  void Release() const UNLOCK_FUNCTION();
+
+  // Volatile to prevent code being optimized away in Acquire()/Release().
+  mutable volatile int access_count_ = 0;
+  mutable volatile PlatformThreadRef accessing_thread_;
+};
+
+namespace internal {
+class SCOPED_LOCKABLE RaceCheckerScope {
+ public:
+  explicit RaceCheckerScope(const RaceChecker* race_checker)
+      EXCLUSIVE_LOCK_FUNCTION(race_checker);
+
+  bool RaceDetected() const;
+  ~RaceCheckerScope() UNLOCK_FUNCTION();
+
+ private:
+  const RaceChecker* const race_checker_;
+  const bool race_check_ok_;
+};
+
+class SCOPED_LOCKABLE RaceCheckerScopeDoNothing {
+ public:
+  explicit RaceCheckerScopeDoNothing(const RaceChecker* race_checker)
+      EXCLUSIVE_LOCK_FUNCTION(race_checker) {}
+
+  ~RaceCheckerScopeDoNothing() UNLOCK_FUNCTION() {}
+};
+
+}  // namespace internal
+}  // namespace rtc
+
+#define RTC_CHECK_RUNS_SYNCHRONIZED(x)             \
+  rtc::internal::RaceCheckerScope race_checker(x); \
+  RTC_CHECK(!race_checker.RaceDetected())
+
+#if RTC_DCHECK_IS_ON
+#define RTC_DCHECK_RUNS_SYNCHRONIZED(x)            \
+  rtc::internal::RaceCheckerScope race_checker(x); \
+  RTC_DCHECK(!race_checker.RaceDetected())
+#else
+#define RTC_DCHECK_RUNS_SYNCHRONIZED(x) \
+  rtc::internal::RaceCheckerScopeDoNothing race_checker(x)
+#endif
+
+#endif  // WEBRTC_BASE_RACE_CHECKER_H_