AudioRendererImpl: Fix data race.

media/renderers/audio_renderer_impl.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/renderers/audio_renderer_impl.h"
 
 #include <math.h>
 #include <stddef.h>
 #include <algorithm>
 #include <utility>
@@ skipping 85 matching lines @@
   // After this call, the |sink_| will not call back into |this| anymore.
   sink_->Stop();
 
   if (!init_cb_.is_null())
     base::ResetAndReturn(&init_cb_).Run(PIPELINE_ERROR_ABORT);
 }
 
 void AudioRendererImpl::StartTicking() {
   DVLOG(1) << __func__;
   DCHECK(task_runner_->BelongsToCurrentThread());
+
+  base::AutoLock auto_lock(lock_);
+
   DCHECK(!rendering_);
   rendering_ = true;
 
-  base::AutoLock auto_lock(lock_);
   // Wait for an eventual call to SetPlaybackRate() to start rendering.
   if (playback_rate_ == 0) {
     DCHECK(!sink_playing_);
     return;
   }
 
   StartRendering_Locked();
 }
 
 void AudioRendererImpl::StartRendering_Locked() {
   DVLOG(1) << __func__;
   DCHECK(task_runner_->BelongsToCurrentThread());
   DCHECK_EQ(state_, kPlaying);
   DCHECK(!sink_playing_);
   DCHECK_NE(playback_rate_, 0.0);
   lock_.AssertAcquired();
 
   sink_playing_ = true;
 
   base::AutoUnlock auto_unlock(lock_);
   sink_->Play();
 }
 
 void AudioRendererImpl::StopTicking() {
   DVLOG(1) << __func__;
   DCHECK(task_runner_->BelongsToCurrentThread());
+
+  base::AutoLock auto_lock(lock_);
+
   DCHECK(rendering_);
   rendering_ = false;
 
-  base::AutoLock auto_lock(lock_);
   // Rendering should have already been stopped with a zero playback rate.
   if (playback_rate_ == 0) {
     DCHECK(!sink_playing_);
     return;
   }
 
   StopRendering_Locked();
 }
 
 void AudioRendererImpl::StopRendering_Locked() {
@@ skipping 823 matching lines @@
   DCHECK_NE(buffering_state_, buffering_state);
   lock_.AssertAcquired();
   buffering_state_ = buffering_state;
 
   task_runner_->PostTask(
       FROM_HERE, base::Bind(&AudioRendererImpl::OnBufferingStateChange,
                             weak_factory_.GetWeakPtr(), buffering_state_));
 }
 
 }  // namespace media