Switch audio synchronization from sleep() based to select() based.

media/audio/audio_device_thread.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_device_thread.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/logging.h"
@@ skipping 11 matching lines @@
 // The actual worker thread implementation.  It's very bare bones and much
 // simpler than SimpleThread (no synchronization in Start, etc) and supports
 // joining the thread handle asynchronously via a provided message loop even
 // after the Thread object itself has been deleted.
 class AudioDeviceThread::Thread
     : public PlatformThread::Delegate,
       public base::RefCountedThreadSafe<AudioDeviceThread::Thread> {
  public:
   Thread(AudioDeviceThread::Callback* callback,
          base::SyncSocket::Handle socket,
-         const char* thread_name);
+         const char* thread_name,
+         bool synchronized_buffers);
 
   void Start();
 
   // Stops the thread.  If |loop_for_join| is non-NULL, the function posts
   // a task to join (close) the thread handle later instead of waiting for
   // the thread.  If loop_for_join is NULL, then the function waits
   // synchronously for the thread to terminate.
   void Stop(base::MessageLoop* loop_for_join);
 
  private:
   friend class base::RefCountedThreadSafe<AudioDeviceThread::Thread>;
   virtual ~Thread();
 
   // Overrides from PlatformThread::Delegate.
   virtual void ThreadMain() OVERRIDE;
 
   // Runs the loop that reads from the socket.
   void Run();
 
  private:
   base::PlatformThreadHandle thread_;
   AudioDeviceThread::Callback* callback_;
   base::CancelableSyncSocket socket_;
   base::Lock callback_lock_;
   const char* thread_name_;
+  const bool synchronized_buffers_;
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 // AudioDeviceThread implementation
 
 AudioDeviceThread::AudioDeviceThread() {
 }
 
 AudioDeviceThread::~AudioDeviceThread() { DCHECK(!thread_.get()); }
 
 void AudioDeviceThread::Start(AudioDeviceThread::Callback* callback,
                               base::SyncSocket::Handle socket,
-                              const char* thread_name) {
+                              const char* thread_name,
+                              bool synchronized_buffers) {
   base::AutoLock auto_lock(thread_lock_);
-  CHECK(thread_.get() == NULL);
-  thread_ = new AudioDeviceThread::Thread(callback, socket, thread_name);
+  CHECK(!thread_);
+  thread_ = new AudioDeviceThread::Thread(
+      callback, socket, thread_name, synchronized_buffers);
   thread_->Start();
 }
 
 void AudioDeviceThread::Stop(base::MessageLoop* loop_for_join) {
   base::AutoLock auto_lock(thread_lock_);
   if (thread_.get()) {
     thread_->Stop(loop_for_join);
     thread_ = NULL;
   }
 }
 
 bool AudioDeviceThread::IsStopped() {
   base::AutoLock auto_lock(thread_lock_);
-  return thread_.get() == NULL;
+  return !thread_;
 }
 
 // AudioDeviceThread::Thread implementation
 AudioDeviceThread::Thread::Thread(AudioDeviceThread::Callback* callback,
                                   base::SyncSocket::Handle socket,
-                                  const char* thread_name)
+                                  const char* thread_name,
+                                  bool synchronized_buffers)
     : thread_(),
       callback_(callback),
       socket_(socket),
-      thread_name_(thread_name) {
+      thread_name_(thread_name),
+      synchronized_buffers_(synchronized_buffers) {
 }
 
 AudioDeviceThread::Thread::~Thread() {
   DCHECK(thread_.is_null());
 }
 
 void AudioDeviceThread::Thread::Start() {
   base::AutoLock auto_lock(callback_lock_);
   DCHECK(thread_.is_null());
   // This reference will be released when the thread exists.
@@ skipping 41 matching lines @@
   }
 
   Run();
 
   // Release the reference for the thread. Note that after this, the Thread
   // instance will most likely be deleted.
   Release();
 }
 
 void AudioDeviceThread::Thread::Run() {
+  uint32 buffer_index = 0;
   while (true) {
     int pending_data = 0;
     size_t bytes_read = socket_.Receive(&pending_data, sizeof(pending_data));
     if (bytes_read != sizeof(pending_data)) {
       DCHECK_EQ(bytes_read, 0U);
       break;
     }
 
-    base::AutoLock auto_lock(callback_lock_);
-    if (callback_)
-      callback_->Process(pending_data);
+    {
+      base::AutoLock auto_lock(callback_lock_);
+      if (callback_)
+        callback_->Process(pending_data);
+    }
+
+    // Let the other end know which buffer we just filled.

[henrika (OOO until Aug 14), 2013/09/13 10:25:44]

Can you add a line about how the renderer and browser "communicates" using this
buffer index.

[DaleCurtis, 2013/10/22 23:13:49]

Done.

+    if (synchronized_buffers_) {
+      ++buffer_index;
+      size_t bytes_sent = socket_.Send(&buffer_index, sizeof(buffer_index));
+      if (bytes_sent != sizeof(buffer_index))
+        break;
+    }
   }
 }
 
 // AudioDeviceThread::Callback implementation
 
 AudioDeviceThread::Callback::Callback(
     const AudioParameters& audio_parameters,
     base::SharedMemoryHandle memory,
     int memory_length,
     int total_segments)
@@ skipping 13 matching lines @@
 }
 
 AudioDeviceThread::Callback::~Callback() {}
 
 void AudioDeviceThread::Callback::InitializeOnAudioThread() {
   MapSharedMemory();
   CHECK(shared_memory_.memory());
 }
 
 }  // namespace media.