//Create a manager
self.manager = [BHManager new];

//––––––––––––––––––––––––––––––––––––––––––––––––––
//Later when a method with a handler is called...
//––––––––––––––––––––––––––––––––––––––––––––––––––
- (void)doAsyncWork:(void(^)(id result, NSError *error)handler
{
  //Any cache checking goes here...

  //The manager returns an array that will contain all the handlers to call.
  NSArray *handlers = BHManagerAddHandler(self.manager,handler,NSStringFromSelector(_cmd)); //We use the selector as a key
  //Continue only if an array is returned 
  if (!handlers) {
    return;
  }

  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    //Do async work
    for(typeof(handler) aHandler in handlers) {
      aHandler(result, error);
    }
  });
}

//Note this block is never executed nor does it need to do anything, 
//just be of the same interface as the passed handlers

[self.manager setSampleHandler:^(id r, NSError *e){}
              forKey:NSStringFromSelector(@selector(doAsyncWork:))];