objective-c-example-4.mm

dispatch_queue_t queue =
  	dispatch_queue_create("com.example.background", DISPATCH_QUEUE_CONCURRENT);

for (int i = 0; i < 50; i++) {
    dispatch_async(queue, ^{
        sleep(3);
        NSLog(@"Block %d finished", i);
    });
}

NSLog(@"Finished Dispatch");

dispatch_barrier_async(queue, ^{
    NSLog(@"Completed");
});
  
NSLog(@"Continuing Execution");