Replaced thread checker with race checker in AudioMixer.

webrtc/modules/audio_mixer/audio_mixer_impl.h

Index: webrtc/modules/audio_mixer/audio_mixer_impl.h
diff --git a/webrtc/modules/audio_mixer/audio_mixer_impl.h b/webrtc/modules/audio_mixer/audio_mixer_impl.h
index 1abc679480e69d35920d39eb1bb68693c622e1ac..b44fddb1dc74289b5f71749004d19e45d2e31977 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_impl.h
+++ b/webrtc/modules/audio_mixer/audio_mixer_impl.h
@@ -17,7 +17,7 @@
 #include "webrtc/api/audio/audio_mixer.h"
 #include "webrtc/base/scoped_ref_ptr.h"
 #include "webrtc/base/thread_annotations.h"
-#include "webrtc/base/thread_checker.h"
+#include "webrtc/base/race_checker.h"
 #include "webrtc/modules/audio_processing/include/audio_processing.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/system_wrappers/include/critical_section_wrapper.h"
@@ -90,23 +90,23 @@ class AudioMixerImpl : public AudioMixer {
   rtc::CriticalSection crit_;
 
   // The current sample frequency and sample size when mixing.
-  int output_frequency_ ACCESS_ON(&thread_checker_);
-  size_t sample_size_ ACCESS_ON(&thread_checker_);
+  int output_frequency_ GUARDED_BY(&race_checker_);

[kwiberg-webrtc, 2016/10/20 09:37:14]

Is the & necessary?

[aleloi, 2016/10/20 09:52:01]

Turns out it isn't. I've removed it.

I looked in thread_annotations.h and couldn't find anything. Then I searched for
what is used in the rest of WebRTC code. We use both, but no address is more
common than address. I checked that it still works by compiling without
acquiring a lock.

[kwiberg-webrtc, 2016/10/20 10:47:13]

👍

+  size_t sample_size_ GUARDED_BY(&race_checker_);
 
   // List of all audio sources. Note all lists are disjunct
   SourceStatusList audio_source_list_ GUARDED_BY(crit_);  // May be mixed.
 
   // Determines if we will use a limiter for clipping protection during
   // mixing.
-  bool use_limiter_ ACCESS_ON(&thread_checker_);
+  bool use_limiter_ GUARDED_BY(&race_checker_);
 
-  uint32_t time_stamp_ ACCESS_ON(&thread_checker_);
+  uint32_t time_stamp_ GUARDED_BY(&race_checker_);
 
-  // Ensures that Mix is called from the same thread.
-  rtc::ThreadChecker thread_checker_;
+  // Checks that Mix is called sequentially.

[aleloi, 2016/10/20 09:24:23]

We cannot *ensure* at compile time, because (if I understand correctly) the race
checker is not guaranteed to detect a race.

+  rtc::RaceChecker race_checker_;

[kwiberg-webrtc, 2016/10/20 09:37:14]

I would move this up to where crit_ is defined, and have a single comment that
describes both of them. (Protecting different parts of a class with different
protection thingies is slightly unusual, and deserves an explanation.)

[aleloi, 2016/10/20 09:52:01]

Moved up and reworded comment.

[kwiberg-webrtc, 2016/10/20 10:47:13]

Excellent.

 
   // Used for inhibiting saturation in mixing.
-  std::unique_ptr<AudioProcessing> limiter_ ACCESS_ON(&thread_checker_);
+  std::unique_ptr<AudioProcessing> limiter_ GUARDED_BY(&race_checker_);
 
   RTC_DISALLOW_COPY_AND_ASSIGN(AudioMixerImpl);
 };