Remove the atomic operations from media::AudioFifo, making it truly thread-unsafe.

This class isn't used in multithreaded fashion anymore.

BUG=NONE

Review URL: https://codereview.chromium.org/337163004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@277796 0039d316-1c4b-4281-b951-d872f2087c98

media/base/audio_fifo.cc

@@ -6,9 +6,6 @@
 
 #include "base/logging.h"
 
-using base::subtle::Atomic32;
-using base::subtle::NoBarrier_Store;
-
 namespace media {
 
 // Given current position in the FIFO, the maximum number of elements in the
@@ -52,7 +49,6 @@ AudioFifo::~AudioFifo() {}
 
 int AudioFifo::frames() const {
   int delta = frames_pushed_ - frames_consumed_;
-  base::subtle::MemoryBarrier();
   return delta;
 }
 
@@ -83,12 +79,7 @@ void AudioFifo::Push(const AudioBus* source) {
     }
   }
 
-  // Ensure the data is *really* written before updating |frames_pushed_|.
-  base::subtle::MemoryBarrier();
-
-  Atomic32 new_frames_pushed = frames_pushed_ + source_size;
-  NoBarrier_Store(&frames_pushed_, new_frames_pushed);
-
+  frames_pushed_ += source_size;
   DCHECK_LE(frames(), max_frames());
   write_pos_ = UpdatePos(write_pos_, source_size, max_frames());
 }
@@ -128,9 +119,7 @@ void AudioFifo::Consume(AudioBus* destination,
     }
   }
 
-  Atomic32 new_frames_consumed = frames_consumed_ + frames_to_consume;
-  NoBarrier_Store(&frames_consumed_, new_frames_consumed);
-
+  frames_consumed_ += frames_to_consume;
   read_pos_ = UpdatePos(read_pos_, frames_to_consume, max_frames());
 }
 

media/base/audio_fifo.h

@@ -5,7 +5,6 @@
 #ifndef MEDIA_BASE_AUDIO_FIFO_H_
 #define MEDIA_BASE_AUDIO_FIFO_H_
 
-#include "base/atomicops.h"
 #include "media/base/audio_bus.h"
 #include "media/base/media_export.h"
 
@@ -15,8 +14,7 @@ namespace media {
 // The maximum number of audio frames in the FIFO is set at construction and
 // can not be extended dynamically.  The allocated memory is utilized as a
 // ring buffer.
-// This class is thread-safe in the limited sense that one thread may call
-// Push(), while a second thread calls Consume().
+// This class is thread-unsafe.
 class MEDIA_EXPORT AudioFifo {
  public:
   // Creates a new AudioFifo and allocates |channels| of length |frames|.
@@ -51,8 +49,8 @@ class MEDIA_EXPORT AudioFifo {
   const int max_frames_;
 
   // Number of actual elements in the FIFO.
-  volatile base::subtle::Atomic32 frames_pushed_;
-  volatile base::subtle::Atomic32 frames_consumed_;
+  int frames_pushed_;
+  int frames_consumed_;
 
   // Current read position.
   int read_pos_;