Sleeping barber with GCD (Grand Central Dispatch)

sleeping-barber.m

int main (int argc, const char * argv[]) {
  dispatch_queue_t waitingChairs = dispatch_queue_create("waitingChairs", 0);
  dispatch_queue_t barber = dispatch_queue_create("barber", 0);
  dispatch_semaphore_t semaphore = dispatch_semaphore_create(3);
  NSInteger ident = 0;
  while (++ident) {
    if (dispatch_semaphore_wait(semaphore, DISPATCH_TIME_NOW) != 0) {
      printf("Customer %d turned away\n", ident);
      continue;
    }
    dispatch_async(waitingChairs, ^{
      printf("Customer %d taking a seat\n", ident);
      dispatch_async(barber, ^{
        dispatch_semaphore_signal(semaphore);
        printf("Shave and a haircut for customer %d\n", ident);
      });
    });
  }
  dispatch_release(waitingChairs);
  dispatch_release(barber);
  dispatch_release(semaphore);
  return 0;
}