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ProcessPool workers hold onto return value of last task in memory #79896

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dchevell mannequin opened this issue Jan 11, 2019 · 2 comments
Closed

ProcessPool workers hold onto return value of last task in memory #79896

dchevell mannequin opened this issue Jan 11, 2019 · 2 comments
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3.8 only security fixes stdlib Python modules in the Lib dir

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@dchevell
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Mannequin

dchevell mannequin commented Jan 11, 2019

BPO 35715
Nosy @brianquinlan, @pitrou, @pablogsal, @dchevell
PRs
  • bpo-35715: Liberate return value of _process_worker #11514
  • bpo-35715: Liberate return value of _process_worker #11514
  • bpo-35715: Liberate return value of _process_worker #11514
  • bpo-35715: Liberate return value of _process_worker #11514
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    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
closed_at = <Date 2019-03-16.22:29:06.895>
created_at = <Date 2019-01-11.08:36:21.237>
labels = ['3.8', 'library']
title = 'ProcessPool workers hold onto return value of last task in memory'
updated_at = <Date 2019-03-16.22:29:06.894>
user = 'https://github.com/dchevell'

    bugs.python.org fields:

    activity = <Date 2019-03-16.22:29:06.894>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2019-03-16.22:29:06.895>
closer = 'pablogsal'
components = ['Library (Lib)']
creation = <Date 2019-01-11.08:36:21.237>
creator = 'dchevell'
dependencies = []
files = []
hgrepos = []
issue_num = 35715
keywords = ['patch', 'patch', 'patch', 'patch']
message_count = 2.0
messages = ['333444', '338105']
nosy_count = 4.0
nosy_names = ['bquinlan', 'pitrou', 'pablogsal', 'dchevell']
pr_nums = ['11514', '11514', '11514', '11514']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue35715'
versions = ['Python 3.8']
    @dchevell
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    dchevell mannequin commented Jan 11, 2019

    ProcessPoolExecutor workers will hold onto the return value of their last task in memory until the next task is received. Since the return value has already been propagated to the parent process's Future or else effectively discarded, this is holding onto objects unnecessarily.

    Simple case to reproduce:

        import concurrent.futures
    import time

    executor = concurrent.futures.ProcessPoolExecutor(max_workers=1)

    def big_val():
        return [{1:1} for i in range(1, 1000000)]

    executor.submit(big_val)

    # Observe the memory usage of the process worker during the sleep interval
    time.sleep(10)

    This should be easily fixed by having the worker explicitly del r after calling _sendback_result as it already does this for call_item

    @dchevell dchevell mannequin added 3.8 only security fixes stdlib Python modules in the Lib dir labels Jan 11, 2019
    @pablogsal
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    New changeset 962bdea by Pablo Galindo (Dave Chevell) in branch 'master':
    bpo-35715: Liberate return value of _process_worker (GH-11514)
    962bdea

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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