remove 2 observer with name

    for (int i = 0; i < 30; i++) {
        __block __weak id ob1 = nil;
        __block __weak id ob2 = nil;
        
        void (^block)(NSNotification *) = ^(NSNotification *note) {
            NSLog(@"got noti %@, ob1: %@, ob2: %@", note.name, ob1, ob2);
            [[NSNotificationCenter defaultCenter] removeObserver:ob1];
            [[NSNotificationCenter defaultCenter] removeObserver:ob2];
        };
        
        ob1 = [[NSNotificationCenter defaultCenter] addObserverForName:@"obbb1" object:nil queue:nil usingBlock:block];
        ob2 = [[NSNotificationCenter defaultCenter] addObserverForName:@"obbb2" object:nil queue:nil usingBlock:block];
        
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(arc4random() % 1000 / 50.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            int k = arc4random() % 100;
            NSLog(@"k %d", k);
            if (k > 50) {
                NSLog(@"post obbb1");
                [[NSNotificationCenter defaultCenter] postNotificationName:@"obbb1" object:nil];
            }
            else {
                NSLog(@"post obbb2");
                [[NSNotificationCenter defaultCenter] postNotificationName:@"obbb2" object:nil];
            }
        });
    }