关于调用dispatch_queue_t和dispatch_sync [英] About calling of dispatch_queue_t and dispatch_sync

问题描述

为什么需要代码if (dispatch_get_current_queue() == socketQueue)?为什么我们不能直接使用dispatch_sync(socketQueue, block) ???

Why the code if (dispatch_get_current_queue() == socketQueue) is needed? why can't we just use dispatch_sync(socketQueue, block) directly???

提前谢谢！

- (BOOL)isConnected
{
__block BOOL result = NO;

dispatch_block_t block = ^{
    result = (flags & kConnected) ? YES : NO;
};

if (dispatch_get_current_queue() == socketQueue)
    block();
else
    dispatch_sync(socketQueue, block);

return result;
}

顺便说一句，代码来自 XMPPFramework

BTW, the code is from XMPPFramework

推荐答案

您无法调用dispatch_sync来调度当前串行队列上的块，因为这将导致死锁. Dispatch_sync会等到该块完成执行，但是它永远不会在当前块完成运行之前开始运行.

You cannot call dispatch_sync to schedule blocks on the current serial queue since this will deadlock. Dispatch_sync waits until the block finished executing, but it will never start to run before the current block finished running.

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