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iOS AFNetworking中使用“信号量”无返回结果

iOS AFNetworking中使用“信号量”无返回结果

作者: 心猿意码_ | 来源:发表于2022-05-12 11:10 被阅读0次

    示例如下:

    - (void)viewDidLoad {
      NSLog(@"开始====%@",@"A");
      [self loadListMenuWithFinishMark:@"A"];
      NSLog(@"开始====%@",@"B");
      [self loadListMenuWithFinishMark:@"B"];
      NSLog(@"开始====%@",@"C");
      [self loadListMenuWithFinishMark:@"C"];
    }
    
    - (void)loadListMenuWithFinishMark:(NSString *)mark{
        // 创建信号量
        dispatch_semaphore_t sema = dispatch_semaphore_create(0);
        NSString *urlString = @"http://www.qubaobei.com/ios/cf/dish_list.php?stage_id=1&limit=20&page=1";
        [[AFHTTPSessionManager manager] GET:urlString parameters:nil headers:nil progress:^(NSProgress * _Nonnull downloadProgress) {
        } success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
            // 发送信号 (+ 1)
            dispatch_semaphore_signal(sema);
            NSLog(@"结束======%@",mark);
        } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
            dispatch_semaphore_signal(sema);
            NSLog(@"结束======%@", mark);
        }];
        // 等待signal执行+1后(>0),才执行wait后的业务
        dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
    }
    

    打印结果:

    2022-05-12 10:35:50.871154+0800 SemaphoreDemo[12896:3290528] 开始====A
    

    原因是:
    如果在主线程运行以上代码,会发现没有结果输出;这是因为AFNetworking回调默认是主线程,这样dispatch_semaphore_waitdispatch_semaphore_signal在同一个线程,这样就死锁了。
    所以以上代码需要放在异步线程执行如下:

    - (void)viewDidLoad {
      dispatch_async(dispatch_get_global_queue(0, 0), ^{
            NSLog(@"开始====%@",@"A");
            [self loadListMenuWithFinishMark:@"A"];
            NSLog(@"开始====%@",@"B");
            [self loadListMenuWithFinishMark:@"B"];
            NSLog(@"开始====%@",@"C");
            [self loadListMenuWithFinishMark:@"C"];
        });
    }
    
    - (void)loadListMenuWithFinishMark:(NSString *)mark{
        // 创建信号量
        dispatch_semaphore_t sema = dispatch_semaphore_create(0);
        NSString *urlString = @"http://www.qubaobei.com/ios/cf/dish_list.php?stage_id=1&limit=20&page=1";
        [[AFHTTPSessionManager manager] GET:urlString parameters:nil headers:nil progress:^(NSProgress * _Nonnull downloadProgress) {
        } success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
            // 发送信号 (+ 1)
            dispatch_semaphore_signal(sema);
            NSLog(@"结束======%@",mark);
        } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
            dispatch_semaphore_signal(sema);
            NSLog(@"结束======%@", mark);
        }];
        // 等待signal执行+1后(>0),才执行wait后的业务
        dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
    }
    

    打印结果:

    2022-05-12 10:29:55.555207+0800 SemaphoreDemo[12269:3284921] 开始====A
    2022-05-12 10:29:55.706748+0800 SemaphoreDemo[12269:3284782] 结束======A
    2022-05-12 10:29:55.706758+0800 SemaphoreDemo[12269:3284921] 开始====B
    2022-05-12 10:29:55.712722+0800 SemaphoreDemo[12269:3284782] 结束======B
    2022-05-12 10:29:55.712728+0800 SemaphoreDemo[12269:3284921] 开始====C
    2022-05-12 10:29:55.715101+0800 SemaphoreDemo[12269:3284782] 结束======C
    

    走过路过,点个👍🏻在走哈!!~~

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