Does dispatch_after block the main thread?

问题

I'm setting a timer so that after a second passes I reset a value for my keyboard extension. The problem is that I feel like the following call is stalling my UI:

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
    [self resetDoubleTapBool];
})

Is there an asynchronous way of doing this, or a better way in general? Thanks!

回答1:

The dispatch_after() call itself does not block. At (or shortly after) the appointed time, the block will be submitted to the main queue. Submitting it doesn't block the main thread. When the main thread next runs its run loop or is idle within dispatch_main(), it will execute the block.

IF your -resetDoubleTapBool method takes any appreciable amount of time, that can stall your UI. That's just the same as any code that runs on the main thread. It's not specific to dispatch_after() or any other part of GCD.

回答2:

According to the function documentation:

This function waits until the specified time and then asynchronously adds block to the specified queue.

来源：https://stackoverflow.com/questions/28382990/does-dispatch-after-block-the-main-thread