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gh-77377: Ensure multiprocessing SemLock is valid for spawn-based Process before serializing it (#107275)

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Ensure multiprocessing SemLock is valid for spawn Process before serializing it.

Creating a multiprocessing SemLock with a fork context, and then trying to pass it to a spawn-created Process, would segfault if not detected early.

---------

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Antoine Pitrou <pitrou@free.fr>
This commit is contained in:
albanD 2023-08-23 16:27:35 -04:00 • committed by GitHub
parent 5d18715765
commit 1700d34d31
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3 changed files with 30 additions and 2 deletions
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9
Lib/multiprocessing/synchronize.py
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@ -50,8 +50,8 @@ class SemLock(object):
def __init__(self, kind, value, maxvalue, *, ctx):
if ctx is None:
ctx = context._default_context.get_context()
name = ctx.get_start_method()
unlink_now = sys.platform == 'win32' or name == 'fork'
self.is_fork_ctx = ctx.get_start_method() == 'fork'
unlink_now = sys.platform == 'win32' or self.is_fork_ctx
for i in range(100):
try:
sl = self._semlock = _multiprocessing.SemLock(
@ -103,6 +103,11 @@ class SemLock(object):
if sys.platform == 'win32':
h = context.get_spawning_popen().duplicate_for_child(sl.handle)
else:
if self.is_fork_ctx:
raise RuntimeError('A SemLock created in a fork context is being '
'shared with a process in a spawn context. This is '
'not supported. Please use the same context to create '
'multiprocessing objects and Process.')
h = sl.handle
return (h, sl.kind, sl.maxvalue, sl.name)