Add thread safety to AudioManagerBase to protect access to the audio thread member variable.

media/audio/audio_output_dispatcher.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_output_dispatcher.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/message_loop.h"
 #include "base/time.h"
 #include "media/audio/audio_io.h"
 
 AudioOutputDispatcher::AudioOutputDispatcher(
     AudioManager* audio_manager, const AudioParameters& params,
     base::TimeDelta close_delay)
     : audio_manager_(audio_manager),
-      message_loop_(audio_manager->GetMessageLoop()),
+      message_loop_(MessageLoop::current()),
       params_(params),
       pause_delay_(base::TimeDelta::FromMilliseconds(
           2 * params.samples_per_packet *
           base::Time::kMillisecondsPerSecond / params.sample_rate)),
       paused_proxies_(0),
       ALLOW_THIS_IN_INITIALIZER_LIST(weak_this_(this)),
       close_timer_(FROM_HERE,
           close_delay,
           weak_this_.GetWeakPtr(),
           &AudioOutputDispatcher::ClosePendingStreams) {
-  DCHECK_EQ(MessageLoop::current(), message_loop_);
+  // We expect to be instantiated on the audio thread.  Otherwise the
+  // message_loop_ member will point to the wrong message loop!
+  DCHECK(audio_manager->GetMessageLoop()->BelongsToCurrentThread());
 }
 
 AudioOutputDispatcher::~AudioOutputDispatcher() {
   DCHECK_EQ(MessageLoop::current(), message_loop_);
 }
 
 bool AudioOutputDispatcher::StreamOpened() {
   DCHECK_EQ(MessageLoop::current(), message_loop_);
   paused_proxies_++;
 
@@ skipping 87 matching lines @@
   for (; it != idle_streams_.end(); ++it)
     (*it)->Close();
   idle_streams_.clear();
 
   it = pausing_streams_.begin();
   for (; it != pausing_streams_.end(); ++it)
     (*it)->Close();
   pausing_streams_.clear();
 }
 
-MessageLoop* AudioOutputDispatcher::message_loop() {
-  return message_loop_;
-}
-
 bool AudioOutputDispatcher::CreateAndOpenStream() {
   AudioOutputStream* stream = audio_manager_->MakeAudioOutputStream(params_);
   if (!stream)
     return false;
 
   if (!stream->Open()) {
     stream->Close();
     return false;
   }
   idle_streams_.push_back(stream);
@@ skipping 13 matching lines @@
 
 // This method is called by |close_timer_|.
 void AudioOutputDispatcher::ClosePendingStreams() {
   DCHECK_EQ(MessageLoop::current(), message_loop_);
 
   while (!idle_streams_.empty()) {
     idle_streams_.back()->Close();
     idle_streams_.pop_back();
   }
 }