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
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index 0000000000000000000000000000000000000000..ab6f2f7694538f4f89cdfdbad469472880955a16
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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(RaceChecker* race_checker)
+      EXCLUSIVE_LOCK_FUNCTION(race_checker) {}
+
+  ~RaceCheckerScopeDoNothing() UNLOCK_FUNCTION() {}
+};
+
+}  // namespace internal
+}  // namespace rtc
+
+#define RTC_CHECK_RUNS_SINGLE_THREADED(x)          \

[danilchap, 2016/06/27 17:58:57]

race checkers doesn't verify it is single thread, it verify it was properly
synchronized (may be by running on same thread, but any other synchronization
method is fine too unlike for thread_checker)

may be rename to RTC_(D)CHECK_RUNS_SYNCHRONIZED
or use more generic name RTC_(D)CHECK_WITH(&race_checker_object);

[pbos-webrtc, 2016/06/27 18:06:39]

For me single threaded means that it's accessed as if only by a single thread.
Tommi, do you have a preferred name for this?

[pbos-webrtc, 2016/06/28 11:04:24]

I replaced this with RUNS_SYNCHRONIZED, I don't remember if that was the
phrasing you used this morning tommi@?

+  rtc::internal::RaceCheckerScope race_checker(x); \
+  RTC_CHECK(!race_checker.RaceDetected())
+
+#if RTC_DCHECK_IS_ON
+#define RTC_DCHECK_RUNS_SINGLE_THREADED(x)         \
+  rtc::internal::RaceCheckerScope race_checker(x); \
+  RTC_DCHECK(!race_checker.RaceDetected())
+#else
+#define RTC_DCHECK_RUNS_SINGLE_THREADED(x) \
+  rtc::internal::RaceCheckerScopeDoNothing race_checker(x)
+#endif
+
+#endif  // WEBRTC_BASE_RACE_CHECKER_H_