如果dispatch_sync不使用其他线程，可以更快吗? [英] If dispatch_sync does not use a different thread, can it be faster?

问题描述

我正在运行这段代码

dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
      NSLog(@"Main Thread? %d", [NSThread isMainThread]);
      // non-trivial non-UI code here

});

NSLog 表示我实际上在主线程上，但是...我的印象是，如果我使用 dispatch_sync <，那么平凡的非UI代码的运行速度会更快/code>(而不是什么).

The NSLog indicates that I'm actually on the main thread, but... my impression is that the non-trivial non-UI code runs much faster if I use dispatch_sync (as opposed to nothing).

如果它在主线程上运行，有什么办法可以更快?

推荐答案

全局并发GCD队列没有排序，将其中一个传递给dispatch_sync()是noop，而dispatch_sync()只会在此直接执行指定的块情况，就好像您写过

The global concurrent GCD queues have no ordering, passing one of them to dispatch_sync() is a noop and dispatch_sync() will just execute the specified block directly in this case, as if you had written

^{...}();

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