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Merge pull request #117 from TomHarte/AudioRace

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Works around what appears to be a bug in Apple's AudioQueue.
This commit is contained in:
Thomas Harte 2017-03-26 20:29:41 -04:00 committed by GitHub
commit 04921e64de
1 changed files with 40 additions and 4 deletions
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44
OSBindings/Mac/Clock Signal/Audio/CSAudioQueue.m
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@ -14,11 +14,23 @@
static NSLock *CSAudioQueueDeallocLock;
/*!
Holds a weak reference to a CSAudioQueue. Used to work around an apparent AudioQueue bug.
See -[CSAudioQueue dealloc].
*/
@interface CSWeakAudioQueuePointer: NSObject
@property(nonatomic, weak) CSAudioQueue *queue;
@end
@implementation CSWeakAudioQueuePointer
@end
@implementation CSAudioQueue
{
AudioQueueRef _audioQueue;
AudioQueueBufferRef _storedBuffers[NumberOfStoredAudioQueueBuffer];
NSLock *_storedBuffersLock;
CSWeakAudioQueuePointer *_weakPointer;
}
#pragma mark - AudioQueue callbacks
@ -53,7 +65,7 @@ static void audioOutputCallback(
// lifecycle -dealloc events to result from it.
if([CSAudioQueueDeallocLock tryLock])
{
CSAudioQueue *queue = (__bridge CSAudioQueue *)inUserData;
CSAudioQueue *queue = ((__bridge CSWeakAudioQueuePointer *)inUserData).queue;
BOOL isRunningDry = NO;
isRunningDry = [queue audioQueue:inAQ didCallbackWithBuffer:inBuffer];
id<CSAudioQueueDelegate> delegate = queue.delegate;
@ -100,11 +112,13 @@ static void audioOutputCallback(
outputDescription.mReserved = 0;
// create an audio output queue along those lines
// create an audio output queue along those lines; see -dealloc re: the CSWeakAudioQueuePointer
_weakPointer = [[CSWeakAudioQueuePointer alloc] init];
_weakPointer.queue = self;
if(!AudioQueueNewOutput(
&outputDescription,
audioOutputCallback,
(__bridge void *)(self),
(__bridge void *)(_weakPointer),
NULL,
kCFRunLoopCommonModes,
0,
@ -125,8 +139,30 @@ static void audioOutputCallback(
- (void)dealloc
{
[CSAudioQueueDeallocLock lock];
if(_audioQueue) AudioQueueDispose(_audioQueue, true);
if(_audioQueue)
{
AudioQueueDispose(_audioQueue, true);
_audioQueue = NULL;
}
[CSAudioQueueDeallocLock unlock];
// Yuck. Horrid hack happening here. At least under macOS v10.12, I am frequently seeing calls to
// my registered audio callback (audioOutputCallback in this case) that occur **after** the call
// to AudioQueueDispose above, even though the second parameter there asks for a synchronous shutdown.
// So this appears to be a bug on Apple's side.
//
// Since the audio callback receives a void * pointer that identifies the class it should branch into,
// it's therefore unsafe to pass 'self'. Instead I pass a CSWeakAudioQueuePointer which points to the actual
// queue. The lifetime of that class is the lifetime of this instance plus 1 second, as effected by the
// artificial dispatch_after below — it serves only to keep pointerSaviour alive for an extra second.
//
// Why a second? That's definitely quite a lot longer than any amount of audio that may be queued. So
// probably safe. As and where Apple's audio queue works properly, CSAudioQueueDeallocLock should provide
// absolute safety; elsewhere the CSWeakAudioQueuePointer provides probabilistic.
CSWeakAudioQueuePointer *pointerSaviour = _weakPointer;
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
[pointerSaviour hash];
});
}
#pragma mark - Audio enqueuer