当使用暂停、取消任务时，需要等到正在执行的任务执行完成后，才会执行这个动作。其中取消任务的动作不可逆，取消之后任务不能重新开启。具体代码如下：

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    //当self.operationQueue.suspended 为YES时执行任务，为NO时暂停任务
    //每个任务都有执行状态，暂停的时候正在执行的任务执行完，才会暂停
    self.operationQueue.suspended = !self.operationQueue.suspended;
    
    //取消所有的任务，正在执行的任务执行完，才会执行这个动作，和暂停类似。该方法不可逆，取消后不能恢复执行
//    [self.operationQueue  cancelAllOperations];
}


//NSOperationQueue，最大并发数
- (void)operationQueueMaxConcurrentOperationCount
{
    //1:创建队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    /*
     默认是并发队列，如果最大并发数>1，并发
     如果最大并发数==1，串行
     系统默认的并发数是-1，所有任务全部并发执行
     */
    queue.maxConcurrentOperationCount = 1;
    //2:封装操作
    NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1.0];
        NSLog(@"1------%@",[NSThread currentThread]);
    }];
    NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1.0];
        NSLog(@"2------%@",[NSThread currentThread]);
    }];
    NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1.0];
        NSLog(@"3------%@",[NSThread currentThread]);
    }];
    NSBlockOperation *op4 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1.0];
        NSLog(@"4------%@",[NSThread currentThread]);
    }];
    NSBlockOperation *op5 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1.0];
        NSLog(@"5------%@",[NSThread currentThread]);
    }];
    NSBlockOperation *op6 = [NSBlockOperation blockOperationWithBlock:^{
        [NSThread sleepForTimeInterval:1.0];
        NSLog(@"6------%@",[NSThread currentThread]);
    }];
    
    //3:把操作添加到队列
    [queue addOperation:op1];
    [queue addOperation:op2];
    [queue addOperation:op3];
    [queue addOperation:op4];
    [queue addOperation:op5];
    [queue addOperation:op6];
    self.operationQueue = queue;
}