dispatch_async timeout method call - ios

Question

Is there a good way to call an external method after a set time limit for completing the long process outlined below? I would like the long process to stop trying after a set interval and call a method to try something else and wrap up the request.
dispatch_async(dispatch_get_global_queue(0, 0), ^{
//// LONG PROCESS
dispatch_async(dispatch_get_main_queue(), ^{
//// RESULTS PROCESS
});
});

Answer 1

In order to "kill" the process that's running your block, you'll have to check a condition. This will allow you to do cleanup. Consider the following modifications:
dispatch_async(dispatch_get_global_queue(0, 0), ^{
BOOL finished = NO;
__block BOOL cancelled = NO;
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 5.0 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
if (!finished) {
cancelled = YES;
}
});
void (^cleanup)() = ^{
// CLEANUP
};
//// LONG PROCESS PORTION #1
if (cancelled) {
cleanup();
return;
}
//// LONG PROCESS PORTION #2
if (cancelled) {
cleanup();
return;
}
// etc.
finished = YES;
dispatch_async(dispatch_get_main_queue(), ^{
//// RESULTS PROCESS
});
});

Answer 2

In the ////Long Process change a boolean value (like BOOL finished) to true when finished.
After the call to dispatch_async(...) you typed here, add this:
int64_t delay = 20.0; // In seconds
dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, delay * NSEC_PER_SEC);
dispatch_after(time, dispatch_get_main_queue(), ^(void){
if (!finished) {
//// Stop process and timeout
}
});
In this way, after 20 seconds (or any time you want) you can check if the process is still loading and take some provisions.

Answer 3

I've used this method for Swift:
let delay = 0.33 * Double(NSEC_PER_SEC)
let time = dispatch_time(DISPATCH_TIME_NOW, Int64(delay))
dispatch_after(time, dispatch_get_main_queue()) {
//// RESULTS PROCESS
}