线程等待

dispatch_group_tgroup = dispatch_group_create();

   dispatch_semaphore_t sema = dispatch_semaphore_create(0);

   dispatch_group_async(group,dispatch_queue_create("com.dispatch.test",DISPATCH_QUEUE_CONCURRENT), ^{

       NSURLRequest *request = [[NSURLRequestalloc]initWithURL:[NSURLURLWithString:@"https://www.baidu.com"]];

       NSURLSessionDownloadTask *task = [[NSURLSessionsharedSession]downloadTaskWithRequest:requestcompletionHandler:^(NSURL* _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {

           // 请求完成，可以通知界面刷新界面等操作

           NSLog(@"第一步网络请求完成");

           

        }];

        [taskresume];

       // 以下还要进行一些其他的耗时操作

       NSLog(@"耗时操作继续进行");

       dispatch_semaphore_wait(sema,DISPATCH_TIME_FOREVER);

    });

   dispatch_group_t group1 = dispatch_group_create();

   dispatch_group_async(group1,dispatch_queue_create("com.dispatch.test",DISPATCH_QUEUE_CONCURRENT), ^{

//        dispatch_semaphore_t sema = dispatch_semaphore_create(0);

       NSURLRequest *request = [[NSURLRequestalloc]initWithURL:[NSURLURLWithString:@"https://www.github.com"]];

       NSURLSessionDownloadTask *task = [[NSURLSessionsharedSession]downloadTaskWithRequest:requestcompletionHandler:^(NSURL* _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {

           // 请求完成，可以通知界面刷新界面等操作

           NSLog(@"第二步网络请求完成");

           dispatch_semaphore_signal(sema);

//            dispatch_semaphore_signal(sema);

        }];

        [taskresume];

       // 以下还要进行一些其他的耗时操作

       NSLog(@"耗时操作继续进行");

//        dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);

    });

   dispatch_group_notify(group,dispatch_get_main_queue(), ^{

       NSLog(@"刷新界面等在主线程的操作");

    });

参考文章：http://www.jianshu.com/p/888ea823c8a5