forkserver not reused in child processes

[cchomey]

BPO	42188
Files	test.py

^{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 = None
created_at = <Date 2020-10-29.00:40:06.686>
labels = ['3.8', 'type-bug', 'library']
title = 'forkserver not reused in child processes'
updated_at = <Date 2020-10-29.23:36:31.572>
user = 'https://bugs.python.org/cchomey'

bugs.python.org fields:

activity = <Date 2020-10-29.23:36:31.572>
actor = 'cchomey'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-10-29.00:40:06.686>
creator = 'cchomey'
dependencies = []
files = ['49549']
hgrepos = []
issue_num = 42188
keywords = []
message_count = 1.0
messages = ['379851']
nosy_count = 1.0
nosy_names = ['cchomey']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42188'
versions = ['Python 3.8']

Linked PRs

• gh-86354: Fix child processes not reusing forkserver created by parent #139537

[cchomey]

The docstring on Forkserver.ensure_running states that a child process will use the forkserver process started by its parent:

"""
Make sure that a fork server is running.

This can be called from any process. Note that usually a child
process will just reuse the forkserver started by its parent, so
ensure_running() will do nothing.
"""

Link to definition: https://github.com/python/cpython/blob/master/Lib/multiprocessing/forkserver.py#L105

That is not the behavior that I am seeing, however. I'm seeing each child (that start a process itself) will first spawn a *new* forkserver.