问题描述
此代码
dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
NSLog(@"Main Thread? %d", [NSThread isMainThread]);
});
表明我在主线程中。即使这样做：
shows that I'm in the main thread. Even doing this:
queue = dispatch_queue_create("nonMainQueue", NULL);
仍然报告我在主队列中。这似乎是
still reports that I'm in the main queue. This is, it seems, because I'm using dispatch sync.
这是否意味着我的代码与完全不使用dispatch_sync相同？另外：如果dispatch_sync什么都不做，那又有什么意义呢？
Does this mean that my code is the same as not using dispatch_sync at all? Also: what's the point of dispatch_sync if it does nothing at all, then?
推荐答案
因为队列不是线程，为了检查你是否在主'队列'，你必须使用不同的代码，类似于：
Because queues are not threads, in order to check if you are on the main 'queue', you must use different code, something similar to this:
if (dispatch_get_current_queue() == dispatch_get_main_queue()) {
NSLog(@"On Main Thread!");
}
请注意 dispatch_get_current_queue 已弃用，并且可能会在以后的iOS / Mac OS版本中完全删除。
Just note that dispatch_get_current_queue is deprecated, and is subject to be completely removed in a later iOS/Mac OS version.
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