Use multiple shared memory buffers cyclically for audio capture.

media/audio/audio_device_thread.h

Index: media/audio/audio_device_thread.h
===================================================================
--- media/audio/audio_device_thread.h	(revision 186213)
+++ media/audio/audio_device_thread.h	(working copy)
@@ -8,6 +8,7 @@
 #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"
@@ -36,8 +37,10 @@
   // 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();
 
@@ -49,7 +52,8 @@
     virtual void MapSharedMemory() = 0;
 
     // Called whenever we receive notifications about pending data.
-    virtual void Process(int pending_data) = 0;
+    // The |index| states which shared memory buffer is used.
+    virtual void Process(int pending_data, int index) = 0;
 
    protected:
     // Protected so that derived classes can access directly.
@@ -59,14 +63,14 @@
     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 need_read_index);
   ~AudioDeviceThread();
 
   // Starts the audio thread. The thread must not already be running.
@@ -98,6 +102,9 @@
   //    reliable initialization.
   class Thread;
 
+  // Flag indicating whether need to read index from sync socket.
+  bool need_read_index_;
+
   base::Lock thread_lock_;
   scoped_refptr<AudioDeviceThread::Thread> thread_;