一段简单dispatch_group_async 调用测试代码

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    //参考链接
    //http://www.jianshu.com/p/5617ad407678
    //http://www.jianshu.com/p/56313152e87e
    dispatch_group_t group = dispatch_group_create();
    
    dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);
    
    dispatch_group_enter(group);
    dispatch_group_async(group, queue, ^{
        NSLog(@"%@ start 任务1", [NSThread currentThread]);
        //如下使用 After 是模拟向服务器请求
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            NSLog(@"%@ 任务1", [NSThread currentThread]);
            dispatch_group_leave(group);
        });
    });
    
    dispatch_group_enter(group);
    dispatch_group_async(group, queue, ^{
        NSLog(@"%@ start 任务2", [NSThread currentThread]);
        NSLog(@"%@ 任务2", [NSThread currentThread]);
        dispatch_group_leave(group);
    });
    
    dispatch_group_enter(group);
    dispatch_group_async(group, queue, ^{
        NSLog(@"%@ start 任务3", [NSThread currentThread]);
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            NSLog(@"%@ 任务3", [NSThread currentThread]);
            dispatch_group_leave(group);
        });
    });
    
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"%@ 完成", [NSThread currentThread]);
    });
    
    NSLog(@"%@ 😝😝😝😝😝😝😝", [NSThread currentThread]);
    

}

//将 blockMainThreadTest 放到 主线程中调用 测试
- (void)blockMainThreadTest {
    //如果在主线程中 将任务 派发到 group ，同时采用 group wait 功能的话会导致主线程阻塞，demo 如下
    
//    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ //在其他线程中派发任务到 group 后再采用 group wait 功能则无问题 ； 又或者任务是一个无分叉的代码列，即不是服务请求类型的也可以在主线程中派发任务同时使用 group wait功能而不会导致主线程阻塞
    
        dispatch_group_t group = dispatch_group_create();
        
        dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);
        
        dispatch_group_enter(group);
        dispatch_group_async(group, queue, ^{
            NSLog(@"%@ start 任务1", [NSThread currentThread]);
            //如下使用 After 是模拟向服务器请求
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                NSLog(@"%@ 任务1", [NSThread currentThread]);
                dispatch_group_leave(group);
            });
        });
        
        dispatch_group_enter(group);
        dispatch_group_async(group, queue, ^{
            NSLog(@"%@ start 任务2", [NSThread currentThread]);
            NSLog(@"%@ 任务2", [NSThread currentThread]);
            dispatch_group_leave(group);
        });
        
        dispatch_group_enter(group);
        dispatch_group_async(group, queue, ^{
            NSLog(@"%@ start 任务3", [NSThread currentThread]);
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                NSLog(@"%@ 任务3", [NSThread currentThread]);
                dispatch_group_leave(group);
            });
        });
        
        //    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        //        NSLog(@"%@ 完成", [NSThread currentThread]);
        //    });
        
        dispatch_group_wait(group, DISPATCH_TIME_FOREVER); //等待 group 里的任务都结束后才执行后续代码
        NSLog(@"啦啦啦啦啦");
        NSLog(@"%@ 完成", [NSThread currentThread]);
        
//    });
}