ios - 分派(dispatch)到并发队列导致在主线程上执行？

Question

Apple 的 GCD 文档说明如下:

GCD provides and manages FIFO queues to which your application can submit tasks in the form of block objects. Blocks submitted to dispatch queues are executed on a pool of threads fully managed by the system. No guarantee is made as to the thread on which a task executes. GCD offers three kinds of queues:

这是否意味着即使我发出诸如

之类的请求

dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{...});

它会导致代码块在主线程上执行吗？在那种情况下，似乎在主线程上使用并发队列调用 dispatch_sync 可能会导致主线程卡在等待自身的死锁情况。

我对 GCD 文档的解释是否正确？

Answer 1

是的，如果调用者在主线程上，似乎 dispatch_sync 到全局队列可能意味着在主线程上执行代码。 dispatch_sync 的文档说明:

As an optimization, this function invokes the block on the current thread when possible.

dispatch_sync always scheduling a block on Main Thread