Issue 46787: ProcessPoolExecutor exception memory leak

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This issue has been migrated to GitHub: https://github.com/python/cpython/issues/90943

classification

Title:	ProcessPoolExecutor exception memory leak
Type:	resource usage	Stage:	patch review
Components:	Library (Lib)	Versions:	Python 3.9

process

Status:	open	Resolution:
Dependencies:		Superseder:
Assigned To:		Nosy List:	python-dev, themylogin
Priority:	normal	Keywords:	patch

Created on 2022-02-18 15:16 by themylogin, last changed 2022-04-11 14:59 by admin.

Files
File name	Uploaded	Description	Edit
1.py	themylogin, 2022-02-18 15:16

Pull Requests
URL	Status	Linked	Edit
PR 31408	open	python-dev, 2022-02-18 15:23

Messages (1)
msg413485 - (view)	Author: Vladimir Vinogradenko (themylogin) *	Date: 2022-02-18 15:16
If an exception occurs in ProcessPoolExecutor work item, all the exception frame local variables are not garbage collected (or are garbage collected too lately) because they are referenced by the exception's traceback. Attached file is a test case. With unpatched python 3.9 (debian bullseye) it prints: root@truenas[~/freenas/freenas]# python test.py At iteration 0 memory usage is 226070528 At iteration 1 memory usage is 318763008 At iteration 2 memory usage is 318509056 At iteration 3 memory usage is 321662976 At iteration 4 memory usage is 321404928 At iteration 5 memory usage is 324292608 At iteration 6 memory usage is 324296704 At iteration 7 memory usage is 326922240 At iteration 8 memory usage is 326922240 At iteration 9 memory usage is 329543680 With the proposed patch there is no memory usage growth: At iteration 0 memory usage is 226410496 At iteration 1 memory usage is 226451456 At iteration 2 memory usage is 226451456 At iteration 3 memory usage is 226443264 At iteration 4 memory usage is 226443264 At iteration 5 memory usage is 226435072 At iteration 6 memory usage is 226426880 At iteration 7 memory usage is 226426880 At iteration 8 memory usage is 226435072 At iteration 9 memory usage is 226426880

msg413485 - (view)

Author: Vladimir Vinogradenko (themylogin) *

Date: 2022-02-18 15:16

If an exception occurs in ProcessPoolExecutor work item, all the exception frame local variables are not garbage collected (or are garbage collected too lately) because they are referenced by the exception's traceback.

Attached file is a test case. With unpatched python 3.9 (debian bullseye) it prints:

root@truenas[~/freenas/freenas]# python test.py
At iteration 0 memory usage is 226070528
At iteration 1 memory usage is 318763008
At iteration 2 memory usage is 318509056
At iteration 3 memory usage is 321662976
At iteration 4 memory usage is 321404928
At iteration 5 memory usage is 324292608
At iteration 6 memory usage is 324296704
At iteration 7 memory usage is 326922240
At iteration 8 memory usage is 326922240
At iteration 9 memory usage is 329543680

With the proposed patch there is no memory usage growth:

At iteration 0 memory usage is 226410496
At iteration 1 memory usage is 226451456
At iteration 2 memory usage is 226451456
At iteration 3 memory usage is 226443264
At iteration 4 memory usage is 226443264
At iteration 5 memory usage is 226435072
At iteration 6 memory usage is 226426880
At iteration 7 memory usage is 226426880
At iteration 8 memory usage is 226435072
At iteration 9 memory usage is 226426880

History
Date	User	Action	Args
2022-04-11 14:59:56	admin	set	github: 90943
2022-02-18 15:23:21	python-dev	set	keywords: + patch nosy: + python-dev pull_requests: + pull_request29548 stage: patch review
2022-02-18 15:16:10	themylogin	create