多个网络请求中GCD信号量的使用

    //信号量
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
    //创建全局并行
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    //任务一
    dispatch_group_async(group, queue, ^{
        [self getAdvertList:^{ //这个block是此网络任务异步请求结束时调用的,代表着网络请求的结束.
        //一个任务结束时标记一个信号量
             dispatch_semaphore_signal(semaphore);
        }];
    });
    //任务二
    dispatch_group_async(group, queue, ^{
        [self getHotCultureList:^{
            dispatch_semaphore_signal(semaphore);
        }];
    });
    //任务三
    dispatch_group_async(group, queue, ^{
        [self getSurroundCulture:^{
            dispatch_semaphore_signal(semaphore);
        }];
    });
    //任务四
    dispatch_group_async(group, queue, ^{
        [self getMySubscibe:^{
             dispatch_semaphore_signal(semaphore);
        }];

    });
    //任务五
    dispatch_group_async(group, queue, ^{
        [self getRecommendCulture:^{
             dispatch_semaphore_signal(semaphore);
        }];
    });
    //任务六
    dispatch_group_async(group, queue, ^{
         [self getNews:^{
              dispatch_semaphore_signal(semaphore);
         }];
    });

    dispatch_group_notify(group, queue, ^{
    //6个任务,6个信号等待.
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        //这里就是所有异步任务请求结束后执行的代码
         [self.homeTableView.mj_header endRefreshing];

    });
-(void)getAdvertList:(void(^)())finish{ 
    //网络请求..成功后调用一下finish,失败也调用finish
}