iOS 【GCD实战之多个网络请求的并发】

摘录：iOS开发网络篇：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

        });
    });

第二种 通过请求数量计数

定义一个block

typedef void(^Complete)();
将block作为类的属性

@property (copy, nonatomic) Complete complete;
实现方式：

NSInteger requestCount = 0;

    //第一个网络请求
    [CommodityViewModel getPriceTransformForIntegral:nil onSuccess:^(id data) {
        NSLog(@"duihuan11");
        requestCount++;
        if (self.complete) {
            self.complete();
        }
    } onFailure:^(NSError *error) {
    }];

    //第二个网络请求
    [CommodityViewModel getPriceTransformForIntegral:nil onSuccess:^(id data) {
        NSLog(@"duihuan22");
        requestCount++;
        if (self.complete) {
            self.complete();
        }
    } onFailure:^(NSError *error) {
    }];

    //第三个网络请求
    [CommodityViewModel getPriceTransformForIntegral:nil onSuccess:^(id data) {
        NSLog(@"duihuan33");
        requestCount++;
        if (self.complete) {
            self.complete();
        }
    } onFailure:^(NSError *error) {
    }];

    self.complete = ^{

            //请求网络的数量等于3表示三个网络请求已完成
            if (requestCount == 3) {

                //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

                });

            }

        };

dispatch_group + 信号量

- (void)groupSync
{
    dispatch_group_t group = dispatch_group_create();
    dispatch_group_enter(group);
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
       
        sleep(5);
        NSLog(@"任务一完成");
        dispatch_group_leave(group);
    });
    dispatch_group_enter(group);
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        sleep(8);
        NSLog(@"任务二完成");
        dispatch_group_leave(group);
    });
    dispatch_group_notify(group, dispatch_get_global_queue(0, 0), ^{
        
        NSLog(@"任务完成");
    });
}

- (void)groupSync2
{
    dispatch_queue_t dispatchQueue = dispatch_queue_create("com.shidaiyinuo.NetWorkStudy1", DISPATCH_QUEUE_CONCURRENT);
    dispatch_queue_t globalQueue = dispatch_get_global_queue(0, 0);
    dispatch_group_t dispatchGroup = dispatch_group_create();
    dispatch_group_async(dispatchGroup, dispatchQueue, ^(){
        
        dispatch_async(globalQueue, ^{
           
            sleep(3);
            NSLog(@"任务一完成");
        });

    });
    dispatch_group_async(dispatchGroup, dispatchQueue, ^(){
        
        dispatch_async(globalQueue, ^{
            
            sleep(2);
            NSLog(@"任务二完成");
        });
        
    });
    dispatch_group_notify(dispatchGroup, dispatch_get_main_queue(), ^(){
        NSLog(@"dispatch_group_notify 被执行了");
    });
}

#pragma mark - 等任务1执行完再执行任务2
- (void)groupSync3
{
    __block dispatch_semaphore_t semap = dispatch_semaphore_create(0);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        sleep(5);
        NSLog(@"我是任务一");
        dispatch_semaphore_signal(semap);
        semap = nil;
    });
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        if (dispatch_semaphore_wait(semap, dispatch_time(DISPATCH_TIME_NOW, 30 * NSEC_PER_SEC)))//超时返回非零
        {
            //处理超时  也可以把超时时间设置成forever；会一直等待直到收到信号
        }
        else//不超时返回0
        {
            dispatch_async(dispatch_get_global_queue(0, 0), ^{
                
                NSLog(@"我是任务二");
            });
        }

    });
}

dispach_group的使用