Use multiple shared memory buffers cyclically for audio capture.

media/audio/audio_device_thread.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_AUDIO_AUDIO_DEVICE_THREAD_H_
 #define MEDIA_AUDIO_AUDIO_DEVICE_THREAD_H_
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
 #include "base/shared_memory.h"
 #include "base/sync_socket.h"
 #include "base/synchronization/lock.h"
 #include "media/base/media_export.h"
 #include "media/audio/audio_parameters.h"
 #include "media/audio/shared_memory_util.h"
 
 class MessageLoop;
 
 namespace media {
 class AudioBus;
 
 // Data transfer between browser and render process uses a combination
 // of sync sockets and shared memory. To read from the socket and render
 // data, we use a worker thread, a.k.a. the AudioDeviceThread, which reads
 // data from the browser via the socket and fills the shared memory from the
 // audio thread via the AudioDeviceThread::Callback interface/class.
 // For more details see the documentation in audio_device.h.
 //
 // TODO(tommi): Multiple audio input/output device instances should be able to
 // share the same thread instead of spinning one per instance.
 class MEDIA_EXPORT AudioDeviceThread {
  public:
   // This is the callback interface/base class that Audio[Output|Input]Device
   // implements to render input/output data. The callbacks run on the
   // thread owned by AudioDeviceThread.
   class Callback {
    public:
+    typedef std::vector<base::SharedMemoryHandle> SharedMemoryHandleVector;
+
     Callback(const AudioParameters& audio_parameters,
-             base::SharedMemoryHandle memory,
+             SharedMemoryHandleVector& memory,
              int memory_length);
     virtual ~Callback();
 
     // One time initialization for the callback object on the audio thread.
     void InitializeOnAudioThread();
 
     // Derived implementations must call shared_memory_.Map appropriately
     // before Process can be called.
     virtual void MapSharedMemory() = 0;
 
     // Called whenever we receive notifications about pending data.

[henrika (OOO until Aug 14), 2013/03/04 13:12:51]

No comment about |index|.

[wjia(left Chromium), 2013/03/05 02:40:13]

Done.

-    virtual void Process(int pending_data) = 0;
+    virtual void Process(int pending_data, int index) = 0;
 
    protected:
     // Protected so that derived classes can access directly.
     // The variables are 'const' since values are calculated/set in the
     // constructor and must never change.
     const AudioParameters audio_parameters_;
     const int samples_per_ms_;
     const int bytes_per_ms_;
 
-    base::SharedMemory shared_memory_;
+    ScopedVector<base::SharedMemory> shared_memory_;
     const int memory_length_;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(Callback);
   };
 
-  AudioDeviceThread();
+  AudioDeviceThread(bool read_index);
   ~AudioDeviceThread();
 
   // Starts the audio thread. The thread must not already be running.
   void Start(AudioDeviceThread::Callback* callback,
              base::SyncSocket::Handle socket,
              const char* thread_name);
 
   // This tells the audio thread to stop and clean up the data.
   // The method can stop the thread synchronously or asynchronously.
   // In the latter case, the thread will still be running after Stop()
@@ skipping 11 matching lines @@
  private:
   // Our own private SimpleThread override.  We implement this in a
   // private class so that we get the following benefits:
   // 1) AudioDeviceThread doesn't expose SimpleThread methods.
   //    I.e. the caller can't call Start()/Stop() - which would be bad.
   // 2) We override ThreadMain to add additional on-thread initialization
   //    while still synchronized with SimpleThread::Start() to provide
   //    reliable initialization.
   class Thread;
 
+  // Flag indicating whether need to read index from sync socket.
+  bool read_index_;

[henrika (OOO until Aug 14), 2013/03/04 13:12:51]

It feels odd to use index as name in a flag. When I read the code I did the
error to think that is was an actual index. Also, please add a comment about
this guy always being false on the output side.

[wjia(left Chromium), 2013/03/05 02:40:13]

Changed name to need_read_index_ to be self explained.

+
   base::Lock thread_lock_;
   scoped_refptr<AudioDeviceThread::Thread> thread_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioDeviceThread);
 };
 
 }  // namespace media.
 
 #endif  // MEDIA_AUDIO_AUDIO_DEVICE_THREAD_H_