[Python-Dev] bpo-34837: Multiprocessing.Pool API Extension (original) (raw)

[Python-Dev] bpo-34837: Multiprocessing.Pool API Extension - Pass Data to Workers w/o Globals

Michael Selik michael.selik at gmail.com
Thu Oct 18 12:39:34 EDT 2018

One idea would be for the Pool method to generate a uuid and slap it on the function as an attribute. If a function being passed in doesn't have one, generate one. If it already has one, just pass that instead of pickling. The child process will keep a cache mapping uuids to functions.

I'm still worried about unintended consequences.

On Thu, Oct 18, 2018 at 9:00 AM Michael Selik <michael.selik at gmail.com> wrote:

On Thu, Oct 18, 2018 at 8:35 AM Sean Harrington <seanharr11 at gmail.com> wrote:

The most common use case comes up when passing instance methods (of really big objects!) to Pool.map().

This reminds me of that old joke: "A patient says to the doctor, 'Doctor, it hurts when I ...!' The doctor replies, 'Well, don't do that.'" Further, let me pivot on my idea of qualname...we can use the id of func as the cache key to address your concern, and store this id on the task tuple (i.e. an integer in-lieu of the func previously stored there). Possible. Does the Pool keep a reference to the passed function in the main process? If not, couldn't the garbage collector free that memory location and a new function could replace it? Then it could have the same qualname and id in CPython. Edge case, for sure. Worse, it'd be hard to reproduce as it'd be dependent on the vagaries of memory allocation. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20181018/4d2b7599/attachment.html>

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