Tornado 的绝大部分 API 都不是线程安全的，从其它线程操作会出（各种奇怪的）问题。只有 IOLoop.add_callback 这一个 API 是线程安全的：

It is safe to call this method from any thread at any time, except from a signal handler. Note that this is the only method in IOLoop that makes this thread-safety guarantee; all other interaction with the IOLoop must be done from that IOLoop‘s thread.

你使用 tornado.concurrent.run_on_executor 就可以了。它自动帮你完成扔任务到线程池、得到结果时取回的逻辑。