如何暂停dispatch_queue_t和它创建的队列

I'm creating a program that can, amoung other things, fade in and out music. The problem is that other threads/queues can pause the music, meaning that the fade in and out also need to not only pause, but hold off. I need to be able to pause the "timer" on a dispatch_after (because this is called when the music starts playing in order to tell it when to start fading out, which would need to be delayed if it was paused) and pause a queue itself (in order to pause a fade in or fade out WHILE they're fading in or out)I'm creating a program that can, amoung other t