iOS dispatch_sync

dispatch_sync

Submits a block object for execution on a dispatch queue and waits until that block completes.
提交块对象以在调度队列上执行，并等待该块完成。

Declaration

void dispatch_sync(dispatch_queue_t queue, dispatch_block_t block);

Parameters

• queue

The queue on which to submit the block. This parameter cannot be NULL.
提交块的队列。 
此参数不能为NULL。

• block

The block to be invoked on the target dispatch queue. This parameter cannot be NULL.
要在目标调度队列上调用的块。 
此参数不能为NULL。

Discussion

Submits a block to a dispatch queue for synchronous execution. Unlike dispatch_async, this function does not return until the block has finished. Calling this function and targeting the current queue results in deadlock.
将块提交到调度队列以进行同步执行。 与dispatch_async不同，此功能在块完成之前不会返回。 调用此函数并以当前队列为目标队列会导致死锁。

Unlike with dispatch_async, no retain is performed on the target queue. Because calls to this function are synchronous, it "borrows" the reference of the caller. Moreover, no Block_copy is performed on the block.
与dispatch_async不同，不对目标队列执行持有。 因为调用此函数是同步的，所以它“借用”调用者的引用。 此外，不对块执行Block_copy。

As an optimization, this function invokes the block on the current thread when possible.
作为优化，可能的话此函数会在当前线程上调用块.