关于dispatch_sync block中的线程的问题

![screenshot](https://oss-cn-hangzhou.aliyuncs.com/yqfiles/0213184c0c20852968df33f6a9038a066a58ef36.png)
dispatch_queue_t myQueue = dispatch_queue_create("com.team", NULL);
NSLog(@"task1 == %@",[NSThread currentThread]);
dispatch_sync(myQueue, ^{
` // task2 为什么在主线程执行，不是应该在block追加到的线程执行吗，就像task4一样,block里的线程应该和 dispatch_sync 的第一个参数的线程相同


    NSLog(@"task2 == %@",[NSThread currentThread]);

});

dispatch_async(myQueue, ^{
    NSLog(@"task3 == %@",[NSThread currentThread]);

    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"task4 == %@",[NSThread currentThread]);

    });
});