fix crash in AUAudioOutputStream::Render()

media/audio/mac/audio_low_latency_output_mac.cc

Index: media/audio/mac/audio_low_latency_output_mac.cc
diff --git a/media/audio/mac/audio_low_latency_output_mac.cc b/media/audio/mac/audio_low_latency_output_mac.cc
index af23e6708f9bd2edaa0aae287b798d1b5b31e2a5..5dfb2c057a011b5364460e6b721d0bb99fc51da0 100644
--- a/media/audio/mac/audio_low_latency_output_mac.cc
+++ b/media/audio/mac/audio_low_latency_output_mac.cc
@@ -50,7 +50,8 @@ AUAudioOutputStream::AUAudioOutputStream(
       output_unit_(0),
       output_device_id_(kAudioObjectUnknown),
       volume_(1),
-      hardware_latency_frames_(0) {
+      hardware_latency_frames_(0),
+      stopped_(false) {
   // We must have a manager.
   DCHECK(manager_);
   // A frame is one sample across all channels. In interleaved audio the per
@@ -178,6 +179,7 @@ void AUAudioOutputStream::Start(AudioSourceCallback* callback) {
   if (!output_unit_)
     return;
 
+  stopped_ = false;
   source_ = callback;
 
   AudioOutputUnitStart(output_unit_);
@@ -186,9 +188,14 @@ void AUAudioOutputStream::Start(AudioSourceCallback* callback) {
 void AUAudioOutputStream::Stop() {
   // We request a synchronous stop, so the next call can take some time. In
   // the windows implementation we block here as well.
-  source_ = NULL;
+  if (stopped_)
+    return;
+
+  stopped_ = true;

[Chris Rogers, 2012/03/28 18:55:10]

Should this maybe be set to "true" only after AudioOutputUnitStop() has
returned?

and you can also remove the check down below for stopped_ in the Render() method

[no longer working on chromium, 2012/03/28 19:25:32]

Done.

 
   AudioOutputUnitStop(output_unit_);
+
+  source_ = NULL;
 }
 
 void AUAudioOutputStream::SetVolume(double volume) {
@@ -211,6 +218,9 @@ void AUAudioOutputStream::GetVolume(double* volume) {
 OSStatus AUAudioOutputStream::Render(UInt32 number_of_frames,
                                      AudioBufferList* io_data,
                                      const AudioTimeStamp* output_time_stamp) {
+  if (stopped_)

[no longer working on chromium, 2012/03/27 11:01:32]

I don't use atomic operation here since there is comment requiring not to add
locks in this real-time thread.

[Chris Rogers, 2012/03/28 18:55:10]

Strictly speaking, I don't think it's even necessary to do this check here,
since you're now calling AudioOutputStop() (which is synchronous) before setting
source_ = NULL 

On 2012/03/27 11:01:32, xians1 wrote:

[no longer working on chromium, 2012/03/28 19:25:32]

True, thanks for pointing out. It just feels safer to use a check to make sure
we quit the callback as quickly as possible after Stop() is called. But I agree
this is not necessary.

+    return -1;
+
   // Update the playout latency.
   double playout_latency_frames = GetPlayoutLatency(output_time_stamp);