Fixing multiprocessing memory leak in downbeats.py

[igalcohenhadria]

Moving the multiprocessing pool initialisation to the process area.
(using multiprocessing.pool in the init section cause the pool to never release thus creating zombies)

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[superbock]

That's a bit weird, since I exactly did the opposite — moving the pool creation to __init__() — because it was leaking memory and file descriptors when being set up in process(), at least this is what the comment I left in processors.py suggests.

May I ask in which situations these zombie processes appear?

If there's a problem with zombies, we should probably aim for a dedicated process/pool destruction mechanism or use a dedicated pooling solution which does what we need.

[igalcohenhadria]

Hello, I was using the processor in a simple loop and ended up with a memory allocation failure after a few thousands … I tracked down the problem there and fixed it for me the way I sent in the pool request … I ll try to send you more info tomorrow if you want Envoyé de mon iPhone

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Le 19 juin 2022 à 15:00, Sebastian Böck ***@***.***> a écrit :  That's a bit weird, since I exactly did the opposite — moving the pool creation to __init__() — because it was leaking memory and file descriptors when being set up in process(), at least this is what the comment I left in processors.py suggests. May I ask in which situations these zombie processes appear? If there's a problem with zombies, we should probably aim for a dedicated process/pool destruction mechanism or use a dedicated pooling solution which does what we need. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you authored the thread.

[superbock]

Maybe you can paste a snippet of the code you're using. Using the processor in a loop doesn't sound too efficient... usually it's much better to instantiate the processor only once and then call it either in a loop or with all files at once and let it do the processing (in parallel) for you.

[igalcohenhadria]

Here the code and the running test in a youtube video.

https://www.youtube.com/watch?v=4DY8wW19QrE

The code just loop freely and you will see zombies appearing in the processor counter i made.
Initializing once may be effective to limit the number of zombies, but after python3 stops, zombies would still remains.

Also good practice around multiprocessing is to use the pool inside a "with" or closing the pool at some point manually.

An alternative to the patch i gave would be to keep the pool as an attribute in the init and close the pool in the del())