小编mac*_*lla的帖子

我试图更好地了解队列及其工作原理。这个片段是为了测试他们的行为：

- (void)dispatchQueueTest
{
    NSLog( @"Begin test on %@ thread", [NSThread isMainThread] ? @"main" : @"other" );
    dispatch_semaphore_t s = dispatch_semaphore_create(0);

    dispatch_async( dispatch_get_main_queue(), ^{
        NSLog( @"Signalling semaphore" );
        dispatch_semaphore_signal(s);
    });

    NSLog( @"Waiting for worker" );
    while( dispatch_semaphore_wait( s, DISPATCH_TIME_NOW ) ) {
        NSDate* timeout = [NSDate dateWithTimeIntervalSinceNow:10.f];
        // Process events on the run loop
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:timeout];
    }
    dispatch_release(s);
    NSLog( @"All sync'd up" );
}

正如预期的那样，它会在日志中生成以下内容：

Begin test on main thread
Waiting for worker
Signalling semaphore
All sync'd up …