6个并发队列两两执行

有6个并发队列A1、A2、B1、B2、C1、C2，实现A1、A2执行完后执行B1、B2，B1、B2执行完后执行C1、C2
使用GCD实现

dispatch_queue_t queue = dispatch_queue_create("com.queue", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        NSLog(@"线程A1开始");
        sleep(1);
        NSLog(@"线程A1结束");
    });
    dispatch_async(queue, ^{
        NSLog(@"线程A2开始");
        sleep(1);
        NSLog(@"线程A2结束");
    });
    
    dispatch_barrier_async(queue, ^{
        dispatch_async(queue, ^{
            NSLog(@"线程B1开始");
            sleep(1);
            NSLog(@"线程B1结束");
        });
        dispatch_async(queue, ^{
            NSLog(@"线程B2开始");
            sleep(1);
            NSLog(@"线程B2结束");
        });
        dispatch_barrier_async(queue, ^{
            dispatch_async(queue, ^{
                NSLog(@"线程C1开始");
                sleep(1);
                NSLog(@"线程C1结束");
            });
            dispatch_async(queue, ^{
                NSLog(@"线程C2开始");
                sleep(1);
                NSLog(@"线程C2结束");
            });
        });
    });

2019-03-31 23:18:47.958148+0800 0108数组字典[19814:705465] 线程A1开始
2019-03-31 23:18:47.958154+0800 0108数组字典[19814:705464] 线程A2开始
2019-03-31 23:18:48.962063+0800 0108数组字典[19814:705464] 线程A2结束
2019-03-31 23:18:48.962063+0800 0108数组字典[19814:705465] 线程A1结束
2019-03-31 23:18:48.962383+0800 0108数组字典[19814:705464] 线程B1开始
2019-03-31 23:18:48.962383+0800 0108数组字典[19814:705465] 线程B2开始
2019-03-31 23:18:49.964813+0800 0108数组字典[19814:705464] 线程B1结束
2019-03-31 23:18:49.964814+0800 0108数组字典[19814:705465] 线程B2结束
2019-03-31 23:18:49.965271+0800 0108数组字典[19814:705464] 线程C1开始
2019-03-31 23:18:49.965279+0800 0108数组字典[19814:705465] 线程C2开始
2019-03-31 23:18:50.967723+0800 0108数组字典[19814:705464] 线程C1结束
2019-03-31 23:18:50.967723+0800 0108数组字典[19814:705465] 线程C2结束

使用NSOperation实现相反顺序

NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    queue.maxConcurrentOperationCount = 2;
    
    NSBlockOperation *operationA1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"线程A1开始");
        sleep(1);
        NSLog(@"线程A1结束");
    }];
    NSBlockOperation *operationA2 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"线程A2开始");
        sleep(1);
        NSLog(@"线程A2结束");
    }];
    NSBlockOperation *operationB1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"线程B1开始");
        sleep(1);
        NSLog(@"线程B1结束");
    }];
    NSBlockOperation *operationB2 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"线程B2开始");
        sleep(1);
        NSLog(@"线程B2结束");
    }];
    NSBlockOperation *operationC1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"线程C1开始");
        sleep(1);
        NSLog(@"线程C1结束");
    }];
    NSBlockOperation *operationC2 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"线程C2开始");
        sleep(1);
        NSLog(@"线程C2结束");
    }];
    
    [operationA1 addDependency:operationB1];
    [operationA1 addDependency:operationB2];
    [operationA2 addDependency:operationB1];
    [operationA2 addDependency:operationB2];
    
    [operationB1 addDependency:operationC1];
    [operationB1 addDependency:operationC2];
    [operationB2 addDependency:operationC1];
    [operationB2 addDependency:operationC2];
    
    [queue addOperation:operationA1];
    [queue addOperation:operationA2];
    [queue addOperation:operationB1];
    [queue addOperation:operationB2];
    [queue addOperation:operationC1];
    [queue addOperation:operationC2];

2019-03-31 23:24:51.753819+0800 0108数组字典[19872:715639] 线程C2开始
2019-03-31 23:24:51.753822+0800 0108数组字典[19872:715642] 线程C1开始
2019-03-31 23:24:52.756609+0800 0108数组字典[19872:715642] 线程C1结束
2019-03-31 23:24:52.756614+0800 0108数组字典[19872:715639] 线程C2结束
2019-03-31 23:24:52.756954+0800 0108数组字典[19872:715642] 线程B2开始
2019-03-31 23:24:52.756956+0800 0108数组字典[19872:715641] 线程B1开始
2019-03-31 23:24:53.761289+0800 0108数组字典[19872:715642] 线程B2结束
2019-03-31 23:24:53.761310+0800 0108数组字典[19872:715641] 线程B1结束
2019-03-31 23:24:53.761751+0800 0108数组字典[19872:715641] 线程A2开始
2019-03-31 23:24:53.761755+0800 0108数组字典[19872:715642] 线程A1开始
2019-03-31 23:24:54.764618+0800 0108数组字典[19872:715641] 线程A2结束
2019-03-31 23:24:54.764618+0800 0108数组字典[19872:715642] 线程A1结束