On Mon, Nov 19, 2018 at 8:26 AM Maarten ter Huurne wrote:

On maandag 19 november 2018 12:40:20 CET Darren Govoni wrote:

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Hi, I am using twisted to run my Flask app via WSGI like so.

twistd --pidfile $PORT/pidfile -l $PORT/logfile -n web --port tcp:$PORT --wsgi my.app

Naturally, I have functions representing routes that enter and exit just fine.

However, I notice the twisted daemon process is :"gathering threads". Eventually system runs out of them.

Here's a full status for one twisted server. 504 threads???

I have a server running inside twistd which uses exactly 1 thread after running for a few weeks, so the problem may not be in twistd itself.

I'm using a reverse-proxy HTTP setup though, not WSGI. Maybe the problem is specific to WSGI, Flask or your application?

Twisted's WSGI support definitely uses threads (as this is essentially a requirement of WSGI). It uses the reactor thread pool (if you launch it from the CLI with twistd) which used to be limited to 10 threads. I don't know if the same limit is in place these days. Jean-Paul

On Nov 19, 2018, at 6:16 AM, Darren Govoni wrote:

I tried to find out if there is a way to limit the thread pool size from command line for twisted web and found nothing. Does it exist?

The thread pool is limited to 10. While this is configurable via the API, no command line option is exposed to tune it. (This would be a great contribution if you were so inclined!) It seems likely to me that Flask is spawning background threads for some reason; given the way Twisted's threadpool works, leaks like this are not common. However, anything is possible: you probably want to gather some information about what all those threads are doing. Can you add a route to your Flask application to call https://docs.python.org/3/library/faulthandler.html#dumping-the-traceback https://docs.python.org/3/library/faulthandler.html#dumping-the-traceback and then save the output somewhere? That will at least give you a hint as to whether Twisted's threadpool is at fault, and if it is, what it is blocked doing. -g

Thanks. I added Tipper to my program and will see what it shows when I ping the process. https://pypi.org/project/tipper/ On Thu, Nov 22, 2018 at 6:43 AM Chris Withers wrote:

On 22/11/2018 02:30, Glyph wrote:

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On Nov 19, 2018, at 6:16 AM, Darren Govoni mailto:darrenuspto@gmail.com> wrote:

I tried to find out if there is a way to limit the thread pool size from command line for twisted web and found nothing. Does it exist?

The thread pool is limited to 10. While this is configurable via the API, no command line option is exposed to tune it. (This would be a great contribution if you were so inclined!)

It seems likely to me that Flask is spawning background threads for some reason; given the way Twisted's threadpool works, leaks like this are not common. However, anything is possible: you probably want to gather some information about what all those threads are doing.

Some ideas on this front:

- pstree/ps and strace will tell you at a low level

- http://pyrasite.com/ and then use Python's thread introspection stuff.

cheers,

Chris

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