Re: [tornado] Gracefully Stop PeriodCallback During Shutdown

[Jon Parise]

On Wed, Aug 22, 2012 at 11:03 AM, Calvin <calvin...@gmail.com> wrote:
> Hi all,
>
> I have a PeriodicCallback that makes HTTP requests to an external API via
> SimpleAsyncHTTPClient. Whenever a request is made, it's important to record
> the response in the datatabase; missing a response is bad.
>
> Whenever I shut down the Tornado server, I run the risk of doing so in the
> middle of a request, which would cause my application to miss recording a
> response. Is there a way to gracefully shut down Tornado, but block if the
> PeriodicCallback is currently running?

I use a graceful shutdown process in my application. It blocks for up
to 10 seconds while it waits for IO loop handlers to complete.

Here's the code: https://gist.github.com/3428652

[Calvin]

Ahh this is awesome -- looks like what I was looking for.

But I do one question about how it works.  On line 20 of your gist, you check that there's only a single element in the _handlers list before stopping the ioloop.  Reading through the ioloop code, I can see that PeriodicCallbacks push _Timeouts onto the _timeout queue, but I fail to see how that relates to the _handlers queue.  Why does checking the _handlers queue work here?

Thanks again!

[Jon Parise]

I took a closer look at this code against Tornado 2.3, and it doesn't
behave quite the same way as when I originally wrote it a couple of
years back. For example, the polling behavior doesn't appear to be
working as it once did. I don't know if something changed in the
surrounding code or in Tornado itself, but I'm afraid I don't have the
time to dig into it at the moment.

If you learn anything useful, however, I'd appreciate hearing about it.

[Calvin]

I've taken a look through the code, but haven't been able to figure it out myself.

If anyone else has a couple of clock cycles to spare, I'm sure Jon and I would both really appreciate any help.  Again, the question is about how to poll for the completion of all IO handlers and PeriodicCallbacks before shutting down the IOLoop.

Thanks!

[A. Jesse Jiryu Davis]

Coming to this very late, but I wanted you to know it inspired a use-case for the Lock class in my package, Toro:

https://toro.readthedocs.org/en/latest/examples/lock_example.html

[Calvin]

This is perfect.  Thank you!