Use multiple shared memory buffers cyclically for audio capture.

media/audio/audio_input_ipc.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_INPUT_IPC_H_
 #define MEDIA_AUDIO_AUDIO_INPUT_IPC_H_
 
 #include "base/shared_memory.h"
 #include "base/sync_socket.h"
 #include "media/audio/audio_parameters.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 // Contains IPC notifications for the state of the server side
 // (AudioInputController) audio state changes and when an AudioInputController
 // has been created.  Implemented by AudioInputDevice.
 class MEDIA_EXPORT AudioInputIPCDelegate {
  public:
   // Valid states for the input stream.
   enum State {
     kRecording,
     kStopped,
     kError
   };
 
   // Called when an AudioInputController has been created.
+  // The |socket_handle| is used by the AudioInputController to signal
+  // notifications that more data is available and can optionally provide
+  // parameter changes back.  The AudioInputDevice must read from this socket
+  // and process the shared memory whenever data is read from the socket.
+  virtual void OnStreamCreated(base::SyncSocket::Handle socket_handle,

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

Nothing is mentioned about |total_handles| here.

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

Done.

+                               int total_handles) = 0;
+
+  // Called when an AudioInputController has been created.
   // The shared memory |handle| points to a memory section that's used to
   // transfer data between the AudioInputDevice and AudioInputController
   // objects.  The implementation of OnStreamCreated takes ownership.

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

Add comments about |length| and |index|.

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

Done.

-  // The |socket_handle| is used by the AudioInputController to signal
-  // notifications that more data is available and can optionally provide
-  // parameter changes back.  The AudioInputDevice must read from this socket
-  // and process the shared memory whenever data is read from the socket.
-  virtual void OnStreamCreated(base::SharedMemoryHandle handle,
-                               base::SyncSocket::Handle socket_handle,
-                               int length) = 0;
+  virtual void OnSharedMemoryCreated(base::SharedMemoryHandle handle,
+                                     int length,
+                                     int index) = 0;
 
   // Called when state of an audio stream has changed.
   virtual void OnStateChanged(State state) = 0;
 
   // Called when the input stream volume has changed.
   virtual void OnVolume(double volume) = 0;
 
   // Called when a device has been started on the server side.
   // If the device could not be started, |device_id| will be empty.
   virtual void OnDeviceReady(const std::string& device_id) = 0;
@@ skipping 21 matching lines @@
   // Unregisters a delegate that was previously registered via a call to
   // AddDelegate().  The audio stream should be in a closed state prior to
   // calling this function.
   virtual void RemoveDelegate(int stream_id) = 0;
 
   // Sends a request to create an AudioInputController object in the peer
   // process, identify it by |stream_id| and configure it to use the specified
   // audio |params|.  Once the stream has been created, the implementation must
   // generate a notification to the AudioInputIPCDelegate and call
   // OnStreamCreated().
-  virtual void CreateStream(int stream_id, const AudioParameters& params,
-      const std::string& device_id, bool automatic_gain_control) = 0;
+  virtual void CreateStream(
+      int stream_id,
+      const AudioParameters& params,
+      const std::string& device_id,
+      bool automatic_gain_control,
+      int shared_memory_count) = 0;
 
   // Starts the device on the server side.  Once the device has started,
   // or failed to start, a callback to
   // AudioInputIPCDelegate::OnDeviceReady() must be made.
   virtual void StartDevice(int stream_id, int session_id) = 0;
 
   // Corresponds to a call to AudioInputController::Record() on the server side.
   virtual void RecordStream(int stream_id) = 0;
 
   // Sets the volume of the audio stream.
   virtual void SetVolume(int stream_id, double volume) = 0;
 
   // Closes the audio stream and deletes the matching AudioInputController
   // instance.  Prior to deleting the AudioInputController object, a call to
   // AudioInputController::Close must be made.
   virtual void CloseStream(int stream_id) = 0;
 
  protected:
   virtual ~AudioInputIPC();
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_INPUT_IPC_H_