AVAudioPlayer on background thread - objective-c

Question

I know very little about using background threads, but this seems to play my sound in the way that I need it to as follows:
1) I need this very short sound effect to play repeatedly even if the sound overlaps.
2) I need the sound to be played perfectly on time.
3) I need the loading of the sound to not affect the on-screen graphics by stuttering.
I am currently just trying out this method with one sound, but if successful, I will roll it out to other sound effects that need the same treatment. My question is this: Am I using the background thread properly? Will there be any sort of memory leaks?
Here's the code:
-(void) playAudio {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
NSString *path = [NSString stringWithFormat:#"%#/metronome.mp3", [[NSBundle mainBundle] resourcePath]];
NSURL *metronomeSound = [NSURL fileURLWithPath:path];
_audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:metronomeSound error:nil];
[_audioPlayer prepareToPlay];
[_audioPlayer play];
});
}
//handles collision detection
-(void) didBeginContact:(SKPhysicsContact *)contact {
uint32_t categoryA = contact.bodyA.categoryBitMask;
uint32_t categoryB = contact.bodyB.categoryBitMask;
if (categoryA == kLineCategory || categoryB == kLineCategory) {
NSLog(#"line contact");
[self playAudio];
}
}

Answer 1

I use the AVAudioPlayer and use it asynchronously and in background threads without any problems and no leaks as far as I can tell. However, I have implemented a singleton class that handles all the allocations and keeps an array of AVAudioPlayer instances that also play asynchronously as needed. If you need to play a sound repeatedly, you should allocate an AVAudioPlayer instance for every time you want to play it. In that case, latency will be negligible and you can even play the same sound simultaneously.
Concerning your strategy I think it needs some refinements, in particular if you want to prevent any delays. The main problem is always reading from disk, which is the slowest operation of all and your limiting step.
Thus, I would also implement an array of AVAudioPlayers each already initialized to play a specific sound, in particular if this sound is played often and repeatedly. You could remove those instances of players that are played less often from the array if memory starts to grow and reload them a few seconds before if you can tell which ones will be needed.
And one more thing... Don't forget to lock and unlock the array, if you are going to access it from multiple threads or better yet, create a GCD queue to handle all accesses to the array.