How do I stop Tornado web server?

Question

I\'ve been playing around a bit with the Tornado web server and have come to a point where I want to stop the web server (for example during unit testing). The following sim

Answer 1

If you need this behavior for unit testing, take a look at tornado.testing.AsyncTestCase.

By default, a new IOLoop is constructed for each test and is available as self.io_loop. This IOLoop should be used in the construction of HTTP clients/servers, etc. If the code being tested requires a global IOLoop, subclasses should override get_new_ioloop to return it.

If you need to start and stop an IOLoop for some other purpose and can't call ioloop.stop() from a callback for some reason, a multi-threaded implementation is possible. To avoid race conditions, however, you need to synchronize access to the ioloop, which is actually impossible. Something like the following will result in deadlock:

Thread 1:

with lock:
    ioloop.start()

Thread 2:

with lock:
    ioloop.stop()

because thread 1 will never release the lock (start() is blocking) and thread 2 will wait till the lock is released to stop the ioloop.

The only way to do it is for thread 2 to call ioloop.add_callback(ioloop.stop), which will call stop() on thread 1 in the event loop's next iteration. Rest assured, ioloop.add_callback() is thread-safe.