GCD和NSOperationQueue简单使用，取消和按顺序执

代码如下：

#pragma mark TODO:可取消的group
- (void)test3 {
    dispatch_group_t group =  dispatch_group_create ();
    dispatch_queue_t pp = dispatch_queue_create ("ssss", DISPATCH_QUEUE_SERIAL);

    NSMutableArray *kk = @[].mutableCopy;
    __block dispatch_block_t block111;
    dispatch_apply (10, pp, ^(size_t index) {
        dispatch_block_t block = dispatch_block_create (0, ^{
            NSLog (@"index:%d %@", index, [NSThread currentThread]);
            [kk removeObject:block];
            if (index > 5) {
                for (dispatch_block_t tmp in kk) {
                    dispatch_block_cancel (tmp);
                }
            }
        });

        dispatch_async (pp, block);
        [kk addObject:block];
        dispatch_group_wait (group, DISPATCH_TIME_FOREVER);
    });
    dispatch_group_notify (group, pp, ^{
        NSLog (@"任务已经完成");
    });
}

#pragma mark TODO: 可取消的NSOperationQueue
- (void)test2 {
    NSOperationQueue *oq = [[NSOperationQueue alloc] init];
    NSMutableArray *opArryM = @[].mutableCopy;
    NSBlockOperation *cureent;
    BOOL stop = NO;

    for (int i = 0; i < 10; i++) {
        __block int x = i;
        NSBlockOperation *bo1 = [NSBlockOperation blockOperationWithBlock:^{
            NSLog (@"请求%d", x);

            if (x > 5) {
                [oq cancelAllOperations];
            }
        }];
        if (cureent) {
            [bo1 addDependency:cureent];
            cureent = bo1;
        } else {
            cureent = bo1;
        }
        [opArryM addObject:bo1];
    }

    [oq addOperations:opArryM waitUntilFinished:YES];

    [oq addBarrierBlock:^{
        NSLog (@"执行完成");
    }];

    self.task = oq;
}

- (void)test {
    dispatch_group_t group =  dispatch_group_create ();
    dispatch_queue_t pp = dispatch_queue_create ("ssss", DISPATCH_QUEUE_SERIAL);
    dispatch_group_enter (group);
    dispatch_after (dispatch_time (DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), pp, ^{
        NSLog (@"任务1");
        NSLog (@"任务1===%@", [NSThread currentThread]);
        dispatch_group_leave (group);
    });

    dispatch_group_wait (group, DISPATCH_TIME_FOREVER);
    dispatch_group_enter (group);
    dispatch_after (dispatch_time (DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), pp, ^{
        NSLog (@"任务2");
        NSLog (@"任务2===%@", [NSThread currentThread]);
        dispatch_group_leave (group);
    });

    dispatch_group_wait (group, DISPATCH_TIME_FOREVER);
    dispatch_group_enter (group);
    dispatch_after (dispatch_time (DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), pp, ^{
        NSLog (@"任务3");
        NSLog (@"任务3===%@", [NSThread currentThread]);
        dispatch_group_leave (group);
    });

    dispatch_group_notify (group, dispatch_get_global_queue (0, 0), ^{
        NSLog (@"任务完成");
    });
}

- (void)test1 {
    NSOperationQueue *oq = [[NSOperationQueue alloc] init];
    NSBlockOperation *bo1 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog (@"请求1");
        NSLog (@"请求1===%@", [NSThread currentThread]);
    }];

    NSBlockOperation *bo2 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog (@"请求2");
        NSLog (@"请求2===%@", [NSThread currentThread]);

        [oq cancelAllOperations];
    }];

    NSBlockOperation *bo3 = [NSBlockOperation blockOperationWithBlock:^{
        NSLog (@"请求3");
        NSLog (@"请求3===%@", [NSThread currentThread]);
    }];

    [bo3 addDependency:bo2];
    [bo2 addDependency:bo1];

    [oq addOperations:@[bo3, bo2, bo1] waitUntilFinished:YES];
}