dispatch_sync block中的线程问题

Question

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]);

    });
});

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Answer 1

编译器会有优化，他发现sync方式，就可能直接同一个线程执行