GCD实战之多个网络请求的并发

 // 创建信号量
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
    // 创建全局并行
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_group_t group = dispatch_group_create();
    dispatch_group_async(group, queue, ^{

        // 请求一
        [loginCode getUserInfoWithNick:nil andUserId:kUserId onSuc:^(id data) {
            NSLog(@"yue");
            dispatch_semaphore_signal(semaphore);

        } andFail:^(NSError *error) {
        }];

    });
    dispatch_group_async(group, queue, ^{

        // 请求二
        [CommodityViewModel getPriceTransformForIntegral:nil onSuccess:^(id data) {

            NSLog(@"duihuan11");
            dispatch_semaphore_signal(semaphore);

        } onFailure:^(NSError *error) {
        }];
    });
    dispatch_group_async(group, queue, ^{

        // 请求三
        [CommodityViewModel getPriceTransformForIntegral:nil onSuccess:^(id data) {
            NSLog(@"duihuan22");
            dispatch_semaphore_signal(semaphore);

        } onFailure:^(NSError *error) {
        }];
    });

    dispatch_group_notify(group, queue, ^{

        // 三个请求对应三次信号等待
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
        dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

        //在这里 进行请求后的方法，回到主线程
        dispatch_async(dispatch_get_main_queue(), ^{

            //更新UI操作

        });

    });