Grand Central Dispatch and unit testing

问题

I have written a simple test case that follows Apple's documentation and I am not seeing the results that I'm expecting.

Here's the code:

- (void)testExample2
{
    NSLog(@"1");

    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0); 

    dispatch_async(dispatch_get_main_queue(), ^{
        NSLog(@"3");
             dispatch_semaphore_signal(semaphore);
        });

    NSLog(@"2");
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

    NSLog(@"4");    
    dispatch_release(semaphore);    
}

I would expect to read: 1, 2, 3, 4 but instead my console just shows me 1, 3.

I've been able to work around the issue using DISPATCH_TIME_NOW in a while loop together with a NSLoop hack but the code above should kind of work... right?

Cheers...

UPDATE

I just realised that I should be using a separate queue rather than dispatch_main_queue()

回答1:

Ended up doing the following in my tearDown.

while (dispatch_semaphore_wait(semaphore, DISPATCH_TIME_NOW)) {
    NSLog(@"...Tearing Down Tests..");
    [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
                             beforeDate:[NSDate dateWithTimeIntervalSinceNow:10]];
}
dispatch_release(semaphore);  

and pushing the semaphore creation into the setUp.

来源：https://stackoverflow.com/questions/10733978/grand-central-dispatch-and-unit-testing