You can access the property playing
directly on main thread because the operation is read, so it is safe I think :)
But you can't use it to judge if playback has completed as document says : Important: Do not poll this property to determine when playback has completed, instead implement the specified delegate method
You should use delegate and implement the method - (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag
, if the method is called, it means the player stop.