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

This is is a tentative fix for an issue where the AudioManager can crash while tearing down
the audio thread. I suspect that this happens because more than one cleanup attempts were
made since the class wasn't thread safe. I'm also changing direct access to the thread's
MessageLoop* to use MessageLoopProxy based on the same theory.

BUG=110051
TEST=Run media tests.

Review URL: https://chromiumcodereview.appspot.com/9255017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@118272 0039d316-1c4b-4281-b951-d872f2087c98

16 files changed, 125 insertions, 103 deletions

diff --git a/content/test/webrtc_audio_device_test.cc b/content/test/webrtc_audio_device_test.cc
index d4ea8b7..94c155b 100644
--- a/content/test/webrtc_audio_device_test.cc
+++ b/content/test/webrtc_audio_device_test.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -277,7 +277,8 @@ bool WebRTCAudioDeviceTest::OnMessageReceived(const IPC::Message& message) {
 
 // Posts a final task to the IO message loop and waits for completion.
 void WebRTCAudioDeviceTest::WaitForIOThreadCompletion() {
-  WaitForMessageLoopCompletion(ChildProcess::current()->io_message_loop());
+  WaitForMessageLoopCompletion(
+      ChildProcess::current()->io_message_loop()->message_loop_proxy());
 }
 
 void WebRTCAudioDeviceTest::WaitForAudioManagerCompletion() {
@@ -285,7 +286,8 @@ void WebRTCAudioDeviceTest::WaitForAudioManagerCompletion() {
     WaitForMessageLoopCompletion(audio_manager_->GetMessageLoop());
 }
 
-void WebRTCAudioDeviceTest::WaitForMessageLoopCompletion(MessageLoop* loop) {
+void WebRTCAudioDeviceTest::WaitForMessageLoopCompletion(
+    base::MessageLoopProxy* loop) {
   base::WaitableEvent* event = new base::WaitableEvent(false, false);
   loop->PostTask(FROM_HERE, base::Bind(&base::WaitableEvent::Signal,
                  base::Unretained(event)));
diff --git a/content/test/webrtc_audio_device_test.h b/content/test/webrtc_audio_device_test.h
index d1caead..f821ad6 100644
--- a/content/test/webrtc_audio_device_test.h
+++ b/content/test/webrtc_audio_device_test.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -144,7 +144,7 @@ class WebRTCAudioDeviceTest
   // Posts a final task to the IO message loop and waits for completion.
   void WaitForIOThreadCompletion();
   void WaitForAudioManagerCompletion();
-  void WaitForMessageLoopCompletion(MessageLoop* loop);
+  void WaitForMessageLoopCompletion(base::MessageLoopProxy* loop);
 
   // Convenience getter for gmock.
   MockMediaObserver& media_observer() const {
diff --git a/media/audio/audio_low_latency_input_output_unittest.cc b/media/audio/audio_low_latency_input_output_unittest.cc
index 683bf2b..a989a4e 100644
--- a/media/audio/audio_low_latency_input_output_unittest.cc
+++ b/media/audio/audio_low_latency_input_output_unittest.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -6,6 +6,7 @@
 #include "base/environment.h"
 #include "base/file_util.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/message_loop.h"
 #include "base/path_service.h"
 #include "base/synchronization/lock.h"
 #include "base/test/test_timeouts.h"
@@ -82,8 +83,8 @@ class MockAudioManager : public AudioManagerAnyPlatform {
 
   virtual ~MockAudioManager() {}
 
-  virtual MessageLoop* GetMessageLoop() OVERRIDE {
-    return MessageLoop::current();
+  virtual scoped_refptr<base::MessageLoopProxy> GetMessageLoop() OVERRIDE {
+    return MessageLoop::current()->message_loop_proxy();
   }
 
  private:
diff --git a/media/audio/audio_manager.h b/media/audio/audio_manager.h
index fd59486..b1ca217 100644
--- a/media/audio/audio_manager.h
+++ b/media/audio/audio_manager.h
@@ -16,6 +16,9 @@
 class AudioInputStream;
 class AudioOutputStream;
 class MessageLoop;
+namespace base {
+class MessageLoopProxy;
+}
 
 // Manages all audio resources. In particular it owns the AudioOutputStream
 // objects. Provides some convenience functions that avoid the need to provide
@@ -121,7 +124,7 @@ class MEDIA_EXPORT AudioManager
   virtual bool IsRecordingInProcess() = 0;
 
   // Returns message loop used for audio IO.
-  virtual MessageLoop* GetMessageLoop() = 0;
+  virtual scoped_refptr<base::MessageLoopProxy> GetMessageLoop() = 0;
 
  protected:
   // Called from Create() to initialize the instance.
diff --git a/media/audio/audio_manager_base.cc b/media/audio/audio_manager_base.cc
index 696dd86..9202e58 100644
--- a/media/audio/audio_manager_base.cc
+++ b/media/audio/audio_manager_base.cc
@@ -5,6 +5,8 @@
 #include "media/audio/audio_manager_base.h"
 
 #include "base/bind.h"
+#include "base/message_loop_proxy.h"
+#include "base/threading/thread.h"
 #include "media/audio/audio_output_dispatcher.h"
 #include "media/audio/audio_output_proxy.h"
 
@@ -14,8 +16,7 @@ const char AudioManagerBase::kDefaultDeviceName[] = "Default";
 const char AudioManagerBase::kDefaultDeviceId[] = "default";
 
 AudioManagerBase::AudioManagerBase()
-    : audio_thread_("AudioThread"),
-      num_active_input_streams_(0) {
+    : num_active_input_streams_(0) {
 }
 
 AudioManagerBase::~AudioManagerBase() {
@@ -24,36 +25,45 @@ AudioManagerBase::~AudioManagerBase() {
 
 #ifndef NDEBUG
 void AudioManagerBase::AddRef() const {
-  const MessageLoop* loop = audio_thread_.message_loop();
-  DCHECK(loop == NULL || loop != MessageLoop::current());
+  {
+    base::AutoLock lock(audio_thread_lock_);
+    const MessageLoop* loop = audio_thread_.get() ?
+        audio_thread_->message_loop() : NULL;
+    DCHECK(loop == NULL || loop != MessageLoop::current());
+  }
   AudioManager::AddRef();
 }
 
 void AudioManagerBase::Release() const {
-  const MessageLoop* loop = audio_thread_.message_loop();
-  DCHECK(loop == NULL || loop != MessageLoop::current());
+  {
+    base::AutoLock lock(audio_thread_lock_);
+    const MessageLoop* loop = audio_thread_.get() ?
+        audio_thread_->message_loop() : NULL;
+    DCHECK(loop == NULL || loop != MessageLoop::current());
+  }
   AudioManager::Release();
 }
 #endif
 
 void AudioManagerBase::Init() {
-  CHECK(audio_thread_.Start());
+  base::AutoLock lock(audio_thread_lock_);
+  DCHECK(!audio_thread_.get());
+  audio_thread_.reset(new base::Thread("AudioThread"));
+  CHECK(audio_thread_->Start());
 }
 
 string16 AudioManagerBase::GetAudioInputDeviceModel() {
   return string16();
 }
 
-MessageLoop* AudioManagerBase::GetMessageLoop() {
-  return audio_thread_.message_loop();
+scoped_refptr<base::MessageLoopProxy> AudioManagerBase::GetMessageLoop() {
+  base::AutoLock lock(audio_thread_lock_);
+  return audio_thread_.get() ? audio_thread_->message_loop_proxy() : NULL;
 }
 
 AudioOutputStream* AudioManagerBase::MakeAudioOutputStreamProxy(
     const AudioParameters& params) {
-  DCHECK_EQ(MessageLoop::current(), GetMessageLoop());
-
-  if (!initialized())
-    return NULL;
+  DCHECK(GetMessageLoop()->BelongsToCurrentThread());
 
   scoped_refptr<AudioOutputDispatcher>& dispatcher =
       output_dispatchers_[params];
@@ -88,23 +98,34 @@ bool AudioManagerBase::IsRecordingInProcess() {
 }
 
 void AudioManagerBase::Shutdown() {
-  if (!initialized())
-    return;
+  // To avoid running into deadlocks while we stop the thread, shut it down
+  // via a local variable while not holding the audio thread lock.
+  scoped_ptr<base::Thread> audio_thread;
+  {
+    base::AutoLock lock(audio_thread_lock_);
+    audio_thread_.swap(audio_thread);
+  }
 
-  DCHECK_NE(MessageLoop::current(), GetMessageLoop());
+  if (!audio_thread.get())
+      return;
+
+  CHECK_NE(MessageLoop::current(), audio_thread->message_loop());
 
   // We must use base::Unretained since Shutdown might have been called from
   // the destructor and we can't alter the refcount of the object at that point.
-  GetMessageLoop()->PostTask(FROM_HERE, base::Bind(
+  audio_thread->message_loop()->PostTask(FROM_HERE, base::Bind(
       &AudioManagerBase::ShutdownOnAudioThread,
       base::Unretained(this)));
+
   // Stop() will wait for any posted messages to be processed first.
-  audio_thread_.Stop();
+  audio_thread->Stop();
 }
 
 void AudioManagerBase::ShutdownOnAudioThread() {
-  DCHECK_EQ(MessageLoop::current(), GetMessageLoop());
-
+  // This should always be running on the audio thread, but since we've cleared
+  // the audio_thread_ member pointer when we get here, we can't verify exactly
+  // what thread we're running on.  The method is not public though and only
+  // called from one place, so we'll leave it at that.
   AudioOutputDispatchersMap::iterator it = output_dispatchers_.begin();
   for (; it != output_dispatchers_.end(); ++it) {
     scoped_refptr<AudioOutputDispatcher>& dispatcher = (*it).second;
diff --git a/media/audio/audio_manager_base.h b/media/audio/audio_manager_base.h
index 15e18be..1cba8a8 100644
--- a/media/audio/audio_manager_base.h
+++ b/media/audio/audio_manager_base.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -9,11 +9,16 @@
 
 #include "base/atomic_ref_count.h"
 #include "base/compiler_specific.h"
-#include "base/threading/thread.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/synchronization/lock.h"
 #include "media/audio/audio_manager.h"
 
 class AudioOutputDispatcher;
 
+namespace base {
+class Thread;
+}
+
 // AudioManagerBase provides AudioManager functions common for all platforms.
 class MEDIA_EXPORT AudioManagerBase : public AudioManager {
  public:
@@ -34,7 +39,7 @@ class MEDIA_EXPORT AudioManagerBase : public AudioManager {
 
   virtual void Init() OVERRIDE;
 
-  virtual MessageLoop* GetMessageLoop() OVERRIDE;
+  virtual scoped_refptr<base::MessageLoopProxy> GetMessageLoop() OVERRIDE;
 
   virtual string16 GetAudioInputDeviceModel() OVERRIDE;
 
@@ -66,12 +71,13 @@ class MEDIA_EXPORT AudioManagerBase : public AudioManager {
 
   void ShutdownOnAudioThread();
 
-  bool initialized() { return audio_thread_.IsRunning(); }
-
   // Thread used to interact with AudioOutputStreams created by this
   // audio manger.
-  base::Thread audio_thread_;
+  scoped_ptr<base::Thread> audio_thread_;
+  mutable base::Lock audio_thread_lock_;
 
+  // Map of cached AudioOutputDispatcher instances.  Must only be touched
+  // from the audio thread (no locking).
   AudioOutputDispatchersMap output_dispatchers_;
 
   // Counts the number of active input streams to find out if something else
diff --git a/media/audio/audio_output_controller.cc b/media/audio/audio_output_controller.cc
index 9f6d7da..d087a70 100644
--- a/media/audio/audio_output_controller.cc
+++ b/media/audio/audio_output_controller.cc
@@ -42,10 +42,11 @@ AudioOutputController::AudioOutputController(AudioManager* audio_manager,
 
 AudioOutputController::~AudioOutputController() {
   DCHECK_EQ(kClosed, state_);
-  if (message_loop_ == MessageLoop::current()) {
+  DCHECK(message_loop_);
+
+  if (!message_loop_.get() || message_loop_->BelongsToCurrentThread()) {
     DoStopCloseAndClearStream(NULL);
   } else {
-    DCHECK(message_loop_);
     WaitableEvent completion(true /* manual reset */,
                              false /* initial state */);
     message_loop_->PostTask(FROM_HERE,
@@ -145,7 +146,7 @@ void AudioOutputController::EnqueueData(const uint8* data, uint32 size) {
 }
 
 void AudioOutputController::DoCreate(const AudioParameters& params) {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
 
   // Close() can be called before DoCreate() is executed.
   if (state_ == kClosed)
@@ -185,7 +186,7 @@ void AudioOutputController::DoCreate(const AudioParameters& params) {
 }
 
 void AudioOutputController::DoPlay() {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
 
   // We can start from created or paused state.
   if (state_ != kCreated && state_ != kPaused)
@@ -204,14 +205,14 @@ void AudioOutputController::DoPlay() {
         FROM_HERE,
         base::Bind(&AudioOutputController::PollAndStartIfDataReady,
         weak_this_.GetWeakPtr()),
-        base::TimeDelta::FromMilliseconds(kPollPauseInMilliseconds));
+        kPollPauseInMilliseconds);
   } else {
     StartStream();
   }
 }
 
 void AudioOutputController::PollAndStartIfDataReady() {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
 
   // Being paranoid: do nothing if state unexpectedly changed.
   if ((state_ != kStarting) && (state_ != kPausedWhenStarting))
@@ -232,12 +233,12 @@ void AudioOutputController::PollAndStartIfDataReady() {
         FROM_HERE,
         base::Bind(&AudioOutputController::PollAndStartIfDataReady,
         weak_this_.GetWeakPtr()),
-        base::TimeDelta::FromMilliseconds(kPollPauseInMilliseconds));
+        kPollPauseInMilliseconds);
   }
 }
 
 void AudioOutputController::StartStream() {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
   state_ = kPlaying;
 
   // We start the AudioOutputStream lazily.
@@ -248,7 +249,7 @@ void AudioOutputController::StartStream() {
 }
 
 void AudioOutputController::DoPause() {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
 
   if (stream_)
     stream_->Stop();
@@ -282,7 +283,7 @@ void AudioOutputController::DoPause() {
 }
 
 void AudioOutputController::DoFlush() {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
 
   // TODO(hclam): Actually flush the audio device.
 
@@ -296,7 +297,7 @@ void AudioOutputController::DoFlush() {
 }
 
 void AudioOutputController::DoClose(const base::Closure& closed_task) {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
 
   if (state_ != kClosed) {
     DoStopCloseAndClearStream(NULL);
@@ -312,7 +313,7 @@ void AudioOutputController::DoClose(const base::Closure& closed_task) {
 }
 
 void AudioOutputController::DoSetVolume(double volume) {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
 
   // Saves the volume to a member first. We may not be able to set the volume
   // right away but when the stream is created we'll set the volume.
@@ -332,7 +333,7 @@ void AudioOutputController::DoSetVolume(double volume) {
 }
 
 void AudioOutputController::DoReportError(int code) {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
   if (state_ != kClosed)
     handler_->OnError(this, code);
 }
@@ -415,7 +416,7 @@ void AudioOutputController::SubmitOnMoreData_Locked() {
 }
 
 void AudioOutputController::DoStopCloseAndClearStream(WaitableEvent *done) {
-  DCHECK_EQ(message_loop_, MessageLoop::current());
+  DCHECK(message_loop_->BelongsToCurrentThread());
 
   // Allow calling unconditionally and bail if we don't have a stream_ to close.
   if (stream_ != NULL) {
diff --git a/media/audio/audio_output_controller.h b/media/audio/audio_output_controller.h
index 24de175..f6e5722 100644
--- a/media/audio/audio_output_controller.h
+++ b/media/audio/audio_output_controller.h
@@ -254,7 +254,7 @@ class MEDIA_EXPORT AudioOutputController
   SyncReader* sync_reader_;
 
   // The message loop of audio thread that this object runs on.
-  MessageLoop* message_loop_;
+  scoped_refptr<base::MessageLoopProxy> message_loop_;
 
   // When starting stream we wait for data to become available.
   // Number of times left.
diff --git a/media/audio/audio_output_dispatcher.cc b/media/audio/audio_output_dispatcher.cc
index 8e40277..b1f265b 100644
--- a/media/audio/audio_output_dispatcher.cc
+++ b/media/audio/audio_output_dispatcher.cc
@@ -14,7 +14,7 @@ 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 *
@@ -25,7 +25,9 @@ AudioOutputDispatcher::AudioOutputDispatcher(
           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() {
@@ -133,10 +135,6 @@ void AudioOutputDispatcher::Shutdown() {
   pausing_streams_.clear();
 }
 
-MessageLoop* AudioOutputDispatcher::message_loop() {
-  return message_loop_;
-}
-
 bool AudioOutputDispatcher::CreateAndOpenStream() {
   AudioOutputStream* stream = audio_manager_->MakeAudioOutputStream(params_);
   if (!stream)
diff --git a/media/audio/audio_output_dispatcher.h b/media/audio/audio_output_dispatcher.h
index 08e6893..cf01a31 100644
--- a/media/audio/audio_output_dispatcher.h
+++ b/media/audio/audio_output_dispatcher.h
@@ -69,8 +69,6 @@ class MEDIA_EXPORT AudioOutputDispatcher
   // Called on the audio thread when the AudioManager is shutting down.
   void Shutdown();
 
-  MessageLoop* message_loop();
-
  private:
   friend class AudioOutputProxyTest;
 
diff --git a/media/audio/audio_output_proxy.cc b/media/audio/audio_output_proxy.cc
index e8309cf..29490db 100644
--- a/media/audio/audio_output_proxy.cc
+++ b/media/audio/audio_output_proxy.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -14,17 +14,16 @@ AudioOutputProxy::AudioOutputProxy(AudioOutputDispatcher* dispatcher)
       state_(kCreated),
       physical_stream_(NULL),
       volume_(1.0) {
-  DCHECK_EQ(MessageLoop::current(), dispatcher_->message_loop());
 }
 
 AudioOutputProxy::~AudioOutputProxy() {
-  DCHECK_EQ(MessageLoop::current(), dispatcher_->message_loop());
+  DCHECK(CalledOnValidThread());
   DCHECK(state_ == kCreated || state_ == kClosed);
   DCHECK(!physical_stream_);
 }
 
 bool AudioOutputProxy::Open() {
-  DCHECK_EQ(MessageLoop::current(), dispatcher_->message_loop());
+  DCHECK(CalledOnValidThread());
   DCHECK_EQ(state_, kCreated);
 
   if (!dispatcher_->StreamOpened()) {
@@ -37,7 +36,7 @@ bool AudioOutputProxy::Open() {
 }
 
 void AudioOutputProxy::Start(AudioSourceCallback* callback) {
-  DCHECK_EQ(MessageLoop::current(), dispatcher_->message_loop());
+  DCHECK(CalledOnValidThread());
   DCHECK(physical_stream_ == NULL);
   DCHECK_EQ(state_, kOpened);
 
@@ -54,7 +53,7 @@ void AudioOutputProxy::Start(AudioSourceCallback* callback) {
 }
 
 void AudioOutputProxy::Stop() {
-  DCHECK_EQ(MessageLoop::current(), dispatcher_->message_loop());
+  DCHECK(CalledOnValidThread());
   if (state_ != kPlaying)
     return;
 
@@ -66,7 +65,7 @@ void AudioOutputProxy::Stop() {
 }
 
 void AudioOutputProxy::SetVolume(double volume) {
-  DCHECK_EQ(MessageLoop::current(), dispatcher_->message_loop());
+  DCHECK(CalledOnValidThread());
   volume_ = volume;
   if (physical_stream_) {
     physical_stream_->SetVolume(volume);
@@ -74,12 +73,12 @@ void AudioOutputProxy::SetVolume(double volume) {
 }
 
 void AudioOutputProxy::GetVolume(double* volume) {
-  DCHECK_EQ(MessageLoop::current(), dispatcher_->message_loop());
+  DCHECK(CalledOnValidThread());
   *volume = volume_;
 }
 
 void AudioOutputProxy::Close() {
-  DCHECK_EQ(MessageLoop::current(), dispatcher_->message_loop());
+  DCHECK(CalledOnValidThread());
   DCHECK(state_ == kCreated || state_ == kError || state_ == kOpened);
   DCHECK(!physical_stream_);
 
diff --git a/media/audio/audio_output_proxy.h b/media/audio/audio_output_proxy.h
index af081c1..8e1b350 100644
--- a/media/audio/audio_output_proxy.h
+++ b/media/audio/audio_output_proxy.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -8,6 +8,7 @@
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
+#include "base/threading/non_thread_safe.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_parameters.h"
 
@@ -21,7 +22,9 @@ class AudioOutputDispatcher;
 //
 // AudioOutputProxy uses AudioOutputDispatcher to open and close
 // physical output streams.
-class MEDIA_EXPORT AudioOutputProxy : public AudioOutputStream {
+class MEDIA_EXPORT AudioOutputProxy
+  : public AudioOutputStream,
+    public NON_EXPORTED_BASE(base::NonThreadSafe) {
  public:
   // Caller keeps ownership of |dispatcher|.
   explicit AudioOutputProxy(AudioOutputDispatcher* dispatcher);
diff --git a/media/audio/audio_output_proxy_unittest.cc b/media/audio/audio_output_proxy_unittest.cc
index b2ff1a9..957e77a 100644
--- a/media/audio/audio_output_proxy_unittest.cc
+++ b/media/audio/audio_output_proxy_unittest.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "base/message_loop.h"
+#include "base/message_loop_proxy.h"
 #include "base/threading/platform_thread.h"
 #include "media/audio/audio_output_dispatcher.h"
 #include "media/audio/audio_output_proxy.h"
@@ -50,7 +51,7 @@ class MockAudioManager : public AudioManager {
   MOCK_METHOD0(UnMuteAll, void());
   MOCK_METHOD0(CanShowAudioInputSettings, bool());
   MOCK_METHOD0(ShowAudioInputSettings, void());
-  MOCK_METHOD0(GetMessageLoop, MessageLoop*());
+  MOCK_METHOD0(GetMessageLoop, scoped_refptr<base::MessageLoopProxy>());
   MOCK_METHOD1(GetAudioInputDeviceNames, void(
       media::AudioDeviceNames* device_name));
   MOCK_METHOD0(IsRecordingInProcess, bool());
@@ -69,7 +70,7 @@ class AudioOutputProxyTest : public testing::Test {
   virtual void SetUp() {
     MockAudioManager* manager = new MockAudioManager();
     EXPECT_CALL(*manager, GetMessageLoop())
-        .WillRepeatedly(Return(&message_loop_));
+        .WillRepeatedly(Return(message_loop_.message_loop_proxy()));
     manager_ = manager;
     InitDispatcher(base::TimeDelta::FromMilliseconds(kTestCloseDelayMs));
   }
diff --git a/media/audio/linux/alsa_output.cc b/media/audio/linux/alsa_output.cc
index ef872c0..b3f931d 100644
--- a/media/audio/linux/alsa_output.cc
+++ b/media/audio/linux/alsa_output.cc
@@ -206,7 +206,7 @@ AlsaPcmOutputStream::AlsaPcmOutputStream(const std::string& device_name,
       state_(kCreated),
       volume_(1.0f),
       source_callback_(NULL) {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   // Sanity check input values.
   if ((params.sample_rate > kAlsaMaxSampleRate) || (params.sample_rate <= 0)) {
@@ -235,7 +235,7 @@ AlsaPcmOutputStream::~AlsaPcmOutputStream() {
 }
 
 bool AlsaPcmOutputStream::Open() {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   if (state() == kInError)
     return false;
@@ -293,7 +293,7 @@ bool AlsaPcmOutputStream::Open() {
 }
 
 void AlsaPcmOutputStream::Close() {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   // Sanity check that the transition occurs correctly.  It is safe to
   // continue anyways because all operations for closing are idempotent.
@@ -322,7 +322,7 @@ void AlsaPcmOutputStream::Close() {
 }
 
 void AlsaPcmOutputStream::Start(AudioSourceCallback* callback) {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   CHECK(callback);
 
@@ -361,7 +361,7 @@ void AlsaPcmOutputStream::Start(AudioSourceCallback* callback) {
 }
 
 void AlsaPcmOutputStream::Stop() {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   // Reset the callback, so that it is not called anymore.
   set_source_callback(NULL);
@@ -370,19 +370,19 @@ void AlsaPcmOutputStream::Stop() {
 }
 
 void AlsaPcmOutputStream::SetVolume(double volume) {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   volume_ = static_cast<float>(volume);
 }
 
 void AlsaPcmOutputStream::GetVolume(double* volume) {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   *volume = volume_;
 }
 
 void AlsaPcmOutputStream::BufferPacket(bool* source_exhausted) {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   // If stopped, simulate a 0-length packet.
   if (stop_stream_) {
@@ -473,7 +473,7 @@ void AlsaPcmOutputStream::BufferPacket(bool* source_exhausted) {
 }
 
 void AlsaPcmOutputStream::WritePacket() {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   // If the device is in error, just eat the bytes.
   if (stop_stream_) {
@@ -537,7 +537,7 @@ void AlsaPcmOutputStream::WritePacket() {
 }
 
 void AlsaPcmOutputStream::WriteTask() {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   if (stop_stream_)
     return;
@@ -553,7 +553,7 @@ void AlsaPcmOutputStream::WriteTask() {
 }
 
 void AlsaPcmOutputStream::ScheduleNextWrite(bool source_exhausted) {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   if (stop_stream_)
     return;
@@ -607,7 +607,7 @@ void AlsaPcmOutputStream::ScheduleNextWrite(bool source_exhausted) {
       manager_->GetMessageLoop()->PostDelayedTask(FROM_HERE,
           base::Bind(&AlsaPcmOutputStream::WriteTask,
                      weak_factory_.GetWeakPtr()),
-          base::TimeDelta::FromMilliseconds(next_fill_time_ms));
+          next_fill_time_ms);
     }
   }
 }
@@ -695,7 +695,7 @@ snd_pcm_sframes_t AlsaPcmOutputStream::GetCurrentDelay() {
 }
 
 snd_pcm_sframes_t AlsaPcmOutputStream::GetAvailableFrames() {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   if (stop_stream_)
     return 0;
@@ -809,7 +809,7 @@ bool AlsaPcmOutputStream::CanTransitionTo(InternalState to) {
 
 AlsaPcmOutputStream::InternalState
 AlsaPcmOutputStream::TransitionTo(InternalState to) {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
 
   if (!CanTransitionTo(to)) {
     NOTREACHED() << "Cannot transition from: " << state_ << " to: " << to;
@@ -843,6 +843,6 @@ void AlsaPcmOutputStream::RunErrorCallback(int code) {
 // Changes the AudioSourceCallback to proxy calls to.  Pass in NULL to
 // release ownership of the currently registered callback.
 void AlsaPcmOutputStream::set_source_callback(AudioSourceCallback* callback) {
-  DCHECK_EQ(MessageLoop::current(), manager_->GetMessageLoop());
+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
   source_callback_ = callback;
 }
diff --git a/media/audio/linux/alsa_output_unittest.cc b/media/audio/linux/alsa_output_unittest.cc
index 5b8405a..f1870d2 100644
--- a/media/audio/linux/alsa_output_unittest.cc
+++ b/media/audio/linux/alsa_output_unittest.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -88,8 +88,8 @@ class MockAudioManagerLinux : public AudioManagerLinux {
 
   // We don't mock this method since all tests will do the same thing
   // and use the current message loop.
-  virtual MessageLoop* GetMessageLoop() {
-    return MessageLoop::current();
+  virtual scoped_refptr<base::MessageLoopProxy> GetMessageLoop() OVERRIDE {
+    return MessageLoop::current()->message_loop_proxy();
   }
 };
 
diff --git a/media/audio/linux/audio_manager_linux.cc b/media/audio/linux/audio_manager_linux.cc
index 6aaf591..da24f12 100644
--- a/media/audio/linux/audio_manager_linux.cc
+++ b/media/audio/linux/audio_manager_linux.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -49,17 +49,9 @@ bool AudioManagerLinux::HasAudioInputDevices() {
 
 AudioOutputStream* AudioManagerLinux::MakeAudioOutputStream(
     const AudioParameters& params) {
-  // Early return for testing hook.  Do this before checking for
-  // |initialized_|.
-  if (params.format == AudioParameters::AUDIO_MOCK) {
+  // Early return for testing hook.
+  if (params.format == AudioParameters::AUDIO_MOCK)
     return FakeAudioOutputStream::MakeFakeStream(params);
-  }
-
-  if (!initialized()) {
-    // We should never get here since this method is called on the audio thread.
-    NOTREACHED();
-    return NULL;
-  }
 
   // Don't allow opening more than |kMaxOutputStreams| streams.
   if (active_output_stream_count_ >= kMaxOutputStreams)
@@ -97,9 +89,6 @@ AudioInputStream* AudioManagerLinux::MakeAudioInputStream(
     return FakeAudioInputStream::MakeFakeStream(params);
   }
 
-  if (!initialized())
-    return NULL;
-
   std::string device_name = (device_id == AudioManagerBase::kDefaultDeviceId) ?
       AlsaPcmInputStream::kAutoSelectDevice : device_id;
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kAlsaInputDevice)) {