Use multiple shared memory buffers cyclically for audio capture.

media/audio/audio_input_device.cc

 // 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.
 
 #include "media/audio/audio_input_device.h"
 
 #include "base/bind.h"
 #include "base/message_loop.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/time.h"
 #include "media/audio/audio_manager_base.h"
 #include "media/base/audio_bus.h"
 
 namespace media {
 
+// The number of shared memory buffer segments indicated to browser process
+// in order to avoid data overwriting. This number can be any positive number,
+// dependent how fast the renderer process can pick up captured data from
+// shared memory.
+static const int kRequestedSharedMemoryCount = 10;
+
 // Takes care of invoking the capture callback on the audio thread.
 // An instance of this class is created for each capture stream in
 // OnLowLatencyCreated().
 class AudioInputDevice::AudioThreadCallback
     : public AudioDeviceThread::Callback {
  public:
   AudioThreadCallback(const AudioParameters& audio_parameters,
                       base::SharedMemoryHandle memory,
                       int memory_length,
+                      int total_segments,
                       CaptureCallback* capture_callback);
   virtual ~AudioThreadCallback();
 
   virtual void MapSharedMemory() OVERRIDE;
 
   // Called whenever we receive notifications about pending data.
   virtual void Process(int pending_data) OVERRIDE;
 
  private:
+  int current_segment_id_;
   CaptureCallback* capture_callback_;
   scoped_ptr<AudioBus> audio_bus_;
   DISALLOW_COPY_AND_ASSIGN(AudioThreadCallback);
 };
 
 AudioInputDevice::AudioInputDevice(
     AudioInputIPC* ipc,
     const scoped_refptr<base::MessageLoopProxy>& io_loop)
     : ScopedLoopObserver(io_loop),
       callback_(NULL),
@@ skipping 53 matching lines @@
 void AudioInputDevice::SetAutomaticGainControl(bool enabled) {
   DVLOG(1) << "SetAutomaticGainControl(enabled=" << enabled << ")";
   message_loop()->PostTask(FROM_HERE,
       base::Bind(&AudioInputDevice::SetAutomaticGainControlOnIOThread,
           this, enabled));
 }
 
 void AudioInputDevice::OnStreamCreated(
     base::SharedMemoryHandle handle,
     base::SyncSocket::Handle socket_handle,
-    int length) {
+    int length,
+    int total_segments) {
   DCHECK(message_loop()->BelongsToCurrentThread());
 #if defined(OS_WIN)
   DCHECK(handle);
   DCHECK(socket_handle);
 #else
   DCHECK_GE(handle.fd, 0);
   DCHECK_GE(socket_handle, 0);
 #endif
   DCHECK(length);
   DVLOG(1) << "OnStreamCreated (stream_id=" << stream_id_ << ")";
 
   // We should only get this callback if stream_id_ is valid.  If it is not,
   // the IPC layer should have closed the shared memory and socket handles
   // for us and not invoked the callback.  The basic assertion is that when
   // stream_id_ is 0 the AudioInputDevice instance is not registered as a
   // delegate and hence it should not receive callbacks.
   DCHECK(stream_id_);
 
   base::AutoLock auto_lock(audio_thread_lock_);
 
   DCHECK(audio_thread_.IsStopped());
   audio_callback_.reset(
-      new AudioInputDevice::AudioThreadCallback(audio_parameters_, handle,
-                                                length, callback_));
+      new AudioInputDevice::AudioThreadCallback(
+          audio_parameters_, handle, length, total_segments, callback_));
   audio_thread_.Start(audio_callback_.get(), socket_handle, "AudioInputDevice");
 
   MessageLoop::current()->PostTask(FROM_HERE,
       base::Bind(&AudioInputDevice::StartOnIOThread, this));
 }
 
 void AudioInputDevice::OnVolume(double volume) {
   NOTIMPLEMENTED();
 }
 
@@ skipping 47 matching lines @@
   if (!pending_device_ready_)
     return;
 
   // If AudioInputDeviceManager returns an empty string, it means no device
   // is ready for start.
   if (device_id.empty()) {
     ipc_->RemoveDelegate(stream_id_);
     stream_id_ = 0;
   } else {
     ipc_->CreateStream(stream_id_, audio_parameters_, device_id,
-                       agc_is_enabled_);
+                       agc_is_enabled_, kRequestedSharedMemoryCount);
   }
 
   pending_device_ready_ = false;
   // Notify the client that the device has been started.
   if (event_handler_)
     event_handler_->OnDeviceStarted(device_id);
 }
 
 void AudioInputDevice::OnIPCClosed() {
   ipc_ = NULL;
@@ skipping 11 matching lines @@
   DCHECK_EQ(0, stream_id_);
   if (stream_id_)
     return;
 
   stream_id_ = ipc_->AddDelegate(this);
   // If |session_id_| is not specified, it will directly create the stream;
   // otherwise it will send a AudioInputHostMsg_StartDevice msg to the browser
   // and create the stream when getting a OnDeviceReady() callback.
   if (!session_id_) {
     ipc_->CreateStream(stream_id_, audio_parameters_,
-        AudioManagerBase::kDefaultDeviceId, agc_is_enabled_);
+        AudioManagerBase::kDefaultDeviceId, agc_is_enabled_,
+        kRequestedSharedMemoryCount);
   } else {
     ipc_->StartDevice(stream_id_, session_id_);
     pending_device_ready_ = true;
   }
 }
 
 void AudioInputDevice::SetSessionIdOnIOThread(int session_id) {
   DCHECK(message_loop()->BelongsToCurrentThread());
   session_id_ = session_id;
 }
@@ skipping 53 matching lines @@
 void AudioInputDevice::WillDestroyCurrentMessageLoop() {
   LOG(ERROR) << "IO loop going away before the input device has been stopped";
   ShutDownOnIOThread();
 }
 
 // AudioInputDevice::AudioThreadCallback
 AudioInputDevice::AudioThreadCallback::AudioThreadCallback(
     const AudioParameters& audio_parameters,
     base::SharedMemoryHandle memory,
     int memory_length,
+    int total_segments,
     CaptureCallback* capture_callback)
-    : AudioDeviceThread::Callback(audio_parameters, memory, memory_length),
+    : AudioDeviceThread::Callback(audio_parameters, memory, memory_length,
+                                  total_segments),
+      current_segment_id_(0),
       capture_callback_(capture_callback) {
   audio_bus_ = AudioBus::Create(audio_parameters_);
 }
 
 AudioInputDevice::AudioThreadCallback::~AudioThreadCallback() {
 }
 
 void AudioInputDevice::AudioThreadCallback::MapSharedMemory() {
   shared_memory_.Map(memory_length_);
 }
 
 void AudioInputDevice::AudioThreadCallback::Process(int pending_data) {
   // The shared memory represents parameters, size of the data buffer and the
   // actual data buffer containing audio data. Map the memory into this
   // structure and parse out parameters and the data area.
-  AudioInputBuffer* buffer =
-      reinterpret_cast<AudioInputBuffer*>(shared_memory_.memory());
+  uint8* ptr = static_cast<uint8*>(shared_memory_.memory());
+  ptr += current_segment_id_ * segment_length_;
+  AudioInputBuffer* buffer = reinterpret_cast<AudioInputBuffer*>(ptr);
   DCHECK_EQ(buffer->params.size,
-            memory_length_ - sizeof(AudioInputBufferParameters));
+            segment_length_ - sizeof(AudioInputBufferParameters));
   double volume = buffer->params.volume;
 
   int audio_delay_milliseconds = pending_data / bytes_per_ms_;
   int16* memory = reinterpret_cast<int16*>(&buffer->audio[0]);
   const int bytes_per_sample = sizeof(memory[0]);
 
+  if (++current_segment_id_ >= total_segments_)
+    current_segment_id_ = 0;
+
   // Deinterleave each channel and convert to 32-bit floating-point
   // with nominal range -1.0 -> +1.0.
   audio_bus_->FromInterleaved(memory, audio_bus_->frames(), bytes_per_sample);
 
   // Deliver captured data to the client in floating point format
   // and update the audio-delay measurement.
   capture_callback_->Capture(audio_bus_.get(),
                              audio_delay_milliseconds, volume);
 }
 
 }  // namespace media