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POHow to let a thread A wait until thread B is finished, then continue thread A?
 

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  1. POHow to let a thread A wait until thread B is finished, then continue thread A?
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    <p>Within a thread A I call an asynchronous service, which runs in thread B. The service calls a delegate method once finished. I want thread A to wait until thread B finishes. I used NSCondition for this.</p> <p>This is my set up (skipped the unimportant stuff):</p> <pre><code>-(void)load { self.someCheckIsTrue = YES; self.condition = [[NSCondition alloc] init]; [self.condition lock]; NSLog(@"log1"); Service *service = // set up service [service request:url delegate:self didFinishSelector:@selector(response:)]; while (self.someCheckIsTrue) [self.condition wait]; NSLog(@"log3"); [self.condition unlock]; } -(void)response:(id)data { NSLog(@"log2"); [self.condition lock]; self.someCheckIsTrue = NO; // do something with the response, doesn't matter here [self.condition signal]; [self.condition unlock]; } </code></pre> <p>For some reason, only "log1" is printed, neither "log2" nor "log3". I assume it's why the delegate method <strong>response</strong> is called by the "service thread", which is thread B, whereas <strong>load</strong> is called by thread A.</p> <p>I also tried a Semaphore, but doesn't work either. Here is the code:</p> <pre><code>-(void)load { NSLog(@"log1"); Service *service = // set up service self.sema = dispatch_semaphore_create(0); [service request:url delegate:self didFinishSelector:@selector(response:)]; dispatch_semaphore_wait(self.sema, DISPATCH_TIME_FOREVER); NSLog(@"log3"); } -(void)response:(id)data { NSLog(@"log2"); // do something with the response, doesn't matter here dispatch_semaphore_signal(self.sema); } </code></pre> <p>How can I get this to work?</p>
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    1. COIt looks to me like `service` is just not calling your `response:` method.
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      1. USAaron Brager
    2. COnot impossible, but hard to tell coz the didFinishSelector is supposed to be called in any case, e.g. when the endpoint is not available... etc.
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    3. COWell, if it was called you'd see `log2` at the very least. Have you tried setting any breakpoints?
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