CODEWITHSUNDEEP
iosobjective-cmacoscocoa
vtukhtarov
vtukhtarov

Reputation: 1902

Interesting place in NSTask's source code

In source code of the NSTask I've found interesting place in method waitUntilExit:

- (void) waitUntilExit
{
    NSTimer *timer = nil;

    while ([self isRunning])
    {
        NSDate  *limit = [[NSDate alloc] initWithTimeIntervalSinceNow: 0.1];
        if (timer == nil)
        {
           timer = [NSTimer scheduledTimerWithTimeInterval: 0.1
                                                    target: nil
                                                  selector: @selector(class)
                                                  userInfo: nil
                                                   repeats: YES];
        }

        [[NSRunLoop currentRunLoop] runMode: NSDefaultRunLoopMode
                                 beforeDate: limit];
        RELEASE(limit);
   }
   [timer invalidate];
}

I can't understand purpose of NSTimer here. And whose method class will be called?

Upvotes: 1

Views: 104

Answers (1)

Martin R
Martin R

Reputation: 539955

The timer target is nil, so the selector is actually irrelevant: You can send any message to nil which is then simply discarded.

The compiler only verifies that the selector refers to some known method, in this case the class method of the NSObject protocol.

This dummy timer is necessary for the following runMode statement which otherwise could terminate immediately, as the NSRunLoop documentation states:

If no input sources or timers are attached to the run loop, this method exits immediately and returns NO; otherwise.

Upvotes: 1

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