关于gcd调度组的简单使用

两种写法：

/*
调度组最重要的任务：监听一组任务的完成
 */
-(void)group1{
    //创建调度组
    dispatch_group_t group = dispatch_group_create();
    //创建队列
    dispatch_queue_t t = dispatch_get_global_queue(0, 0);
    //调度组监听队列调度任务
    dispatch_group_async(group, t, ^{
        NSLog(@"download A %@",[NSThread currentThread]);
    });
    dispatch_group_async(group, t, ^{
        NSLog(@"download b %@",[NSThread currentThread]);
    });
    dispatch_group_notify(group, t, ^{
        NSLog(@"come here");
    });
}

-(void)group2{
    //1.创建调度组
    dispatch_group_t group = dispatch_group_create();
    //2.创建队列
    dispatch_queue_t t = dispatch_get_global_queue(0, 0);
    //3.调度组
    //1>入组
    dispatch_group_enter(group);
    dispatch_group_async(group, t, ^{
        NSLog(@"download A %@",[NSThread currentThread]);
        //2>出组
        dispatch_group_leave(group);
    });
    //1>入组
    dispatch_group_enter(group);
    dispatch_group_async(group, t, ^{
        NSLog(@"download A %@",[NSThread currentThread]);
        //2>出组
        dispatch_group_leave(group);
    });
    dispatch_group_notify(group, t, ^{
        NSLog(@"come here");
    });

}