iphone - How do I kill/suspend/close an asyncronous block in GCD?

Question

I've implemented a block that is dispatched asynchronously using GCD as follows:

__block BOOL retValue;
dispatch_async(dispatch_get_global_queue(0, 0), ^{
    retValue = [self GCDHandler:actionName WithServiceType:serviceType :arguments];
});

return retValue;

How do I cancel such a block if it is running for longer than I would like? Is there a way to cancel GCD-dispatched blocks, or provide a timeout to them?

Answer 1

There is no built in way to cancel GCD blocks. They're rather set and forget. One way I've done this in the past is to provide 'tokens' for blocks.

- (NSString*)dispatchCancelable:(dispatch_block_t)block
{
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        if (!checkIfCanceled)
            block();
    }
    return blah; //Create a UUID or something
}

- (void)cancelBlock:(NSString*)token
{
   //Flag something to mark as canceled
}