Avoid shutdown crash if audio thread is hung.

media/audio/audio_manager.cc

Index: media/audio/audio_manager.cc
diff --git a/media/audio/audio_manager.cc b/media/audio/audio_manager.cc
index 87a2b121e5ca0f73d0e8199f59cc16e25b296013..298a5b523a59acedc983781a367f58d17fc72145 100644
--- a/media/audio/audio_manager.cc
+++ b/media/audio/audio_manager.cc
@@ -81,6 +81,11 @@ class AudioManagerHelper : public base::PowerObserver {
                               base::Unretained(this)));
   }
 
+  bool IsAudioThreadHung() const {
+    base::AutoLock lock(hang_lock_);
+    return audio_thread_status_ == THREAD_HUNG;
+  }
+
   base::SingleThreadTaskRunner* monitor_task_runner() const {
     return monitor_task_runner_.get();
   }
@@ -204,6 +209,7 @@ class AudioManagerHelper : public base::PowerObserver {
 
   void HistogramThreadStatus(ThreadStatus status) {
     DCHECK(monitor_task_runner_->BelongsToCurrentThread());
+    hang_lock_.AssertAcquired();
     audio_thread_status_ = status;
     UMA_HISTOGRAM_ENUMERATION("Media.AudioThreadStatus", audio_thread_status_,
                               THREAD_MAX + 1);
@@ -215,7 +221,7 @@ class AudioManagerHelper : public base::PowerObserver {
   scoped_refptr<base::SingleThreadTaskRunner> monitor_task_runner_;
   scoped_refptr<base::SingleThreadTaskRunner> audio_task_runner_;
 
-  base::Lock hang_lock_;
+  mutable base::Lock hang_lock_;

[DaleCurtis, 2017/06/13 23:43:15]

Just don't make the method const.

[alokp, 2017/06/14 17:34:34]

Done.

   bool hang_detection_enabled_ = true;
   base::TimeTicks last_audio_thread_timer_tick_;
   uint32_t failed_pings_ = 0;
@@ -332,8 +338,6 @@ AudioManager* AudioManager::Get() {
 void AudioManager::Shutdown() {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
 
-  // TODO(alokp): Suspend hang monitor.
-
   if (audio_thread_->GetTaskRunner()->BelongsToCurrentThread()) {
     ShutdownOnAudioThread();
   } else {
@@ -341,7 +345,13 @@ void AudioManager::Shutdown() {
         FROM_HERE, base::Bind(&AudioManager::ShutdownOnAudioThread,
                               base::Unretained(this)));
   }
-  audio_thread_->Stop();
+
+  // Do not attempt to stop the audio thread if it is hung.
+  // Otherwise the current thread will hang too: crbug.com/729494
+  if (!GetHelper()->IsAudioThreadHung())
+    audio_thread_->Stop();

[DaleCurtis, 2017/06/13 23:43:15]

~audio_thread_ will still call stop now. You need to
audio_thread_->ReleaseSoon(audio_thread_) or post it to another thread for
destruction.

[alokp, 2017/06/14 17:34:35]

Good catch. I followed your suggestion of leaking the AudioManager instance
which should take care of this.

+  // TODO(alokp): Suspend hang monitor.
+
   shutdown_ = true;
 }