https://github.com/python/cpython/commit/c2202a7e661d40b1837cc0109cdb9ab40ec4e486
commit: c2202a7e661d40b1837cc0109cdb9ab40ec4e486
branch: main
author: AN Long <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2025-12-23T19:28:32Z
summary:
gh-109263: Start process from spawn context in multiprocessing no longer have
side effect (GH-135813)
files:
A Misc/NEWS.d/next/Library/2025-06-22-18-57-19.gh-issue-109263.f92V95.rst
M Lib/multiprocessing/spawn.py
M Lib/test/_test_multiprocessing.py
diff --git a/Lib/multiprocessing/spawn.py b/Lib/multiprocessing/spawn.py
index daac1ecc34b55e..d43864c939cb63 100644
--- a/Lib/multiprocessing/spawn.py
+++ b/Lib/multiprocessing/spawn.py
@@ -184,7 +184,7 @@ def get_preparation_data(name):
sys_argv=sys.argv,
orig_dir=process.ORIGINAL_DIR,
dir=os.getcwd(),
- start_method=get_start_method(),
+ start_method=get_start_method(allow_none=True),
)
# Figure out whether to initialise main in the subprocess as a module
diff --git a/Lib/test/_test_multiprocessing.py
b/Lib/test/_test_multiprocessing.py
index d03eb1dfb253ec..c8c386101a0669 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -5967,6 +5967,26 @@ def test_context(self):
self.assertRaises(ValueError, ctx.set_start_method, None)
self.check_context(ctx)
+ @staticmethod
+ def _dummy_func():
+ pass
+
+ @warnings_helper.ignore_fork_in_thread_deprecation_warnings()
+ def test_spawn_dont_set_context(self):
+ # Run a process with spawn or forkserver context may change
+ # the global start method, see gh-109263.
+ for method in ('fork', 'spawn', 'forkserver'):
+ multiprocessing.set_start_method(None, force=True)
+
+ try:
+ ctx = multiprocessing.get_context(method)
+ except ValueError:
+ continue
+ process = ctx.Process(target=self._dummy_func)
+ process.start()
+ process.join()
+
self.assertIsNone(multiprocessing.get_start_method(allow_none=True))
+
def test_context_check_module_types(self):
try:
ctx = multiprocessing.get_context('forkserver')
diff --git
a/Misc/NEWS.d/next/Library/2025-06-22-18-57-19.gh-issue-109263.f92V95.rst
b/Misc/NEWS.d/next/Library/2025-06-22-18-57-19.gh-issue-109263.f92V95.rst
new file mode 100644
index 00000000000000..6b96b5b9b2a0de
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-06-22-18-57-19.gh-issue-109263.f92V95.rst
@@ -0,0 +1,2 @@
+Starting a process from spawn context in :mod:`multiprocessing` no longer
+sets the start method globally.
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