Tricks with grand central dispatch

gcd.m

// Using grand central dispatch (GCD) so we don't block the GUI
dispatch_async(dispatch_get_global_queue(0, 0), ^{
    
    // Background, long stuff runs here, but doesn't affect the GUI
    
    dispatch_async(dispatch_get_main_queue(), ^{

        // The GUI thread stuff goes here
        [self.tableView reloadData]; // example
		
    });
});


// Just like javascript's setTimeout: call a block after a delay, on the main thread:
dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_SEC * 0.5); // Make it happen in half a second
dispatch_after(delay, dispatch_get_main_queue(), ^(void){
    // This will happen after the delay
});