Waiting on asynchronous results without blocking the run loop

gistfile1.m

// This is a useful bit of code for waiting for the results of an
// asynchronous operation. It's especially useful in unit tests.
// It keeps the run loop going, so it's not blocking delegate callbacks.

BOOL waitForBlock(NSTimeInterval timeout,
                         BOOL (^condition)(void)) {
    NSDate *timeoutDate = [NSDate dateWithTimeIntervalSinceNow:timeout];
    BOOL val = condition();
    while ( val == NO && [timeoutDate timeIntervalSinceNow] > 0 ) { 
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:timeoutDate];
        val = condition();
    }
    return val;
}

// Use like this:

__block id someObject = nil;
[self doSomethingAsynchronousWithBlock:^(id theResult) {
   someObject = theResult;
}];
BOOL succeeded = waitForBlock(5, ^{ return someObject != nil; });

// if succeeded == NO, then the block never returned YES