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GH-84559: Deprecate fork being the multiprocessing default. #100618

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Merged
gpshead merged 23 commits into from
Feb 2, 2023
Merged

GH-84559: Deprecate fork being the multiprocessing default. #100618

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1cecbdb
GH-84559: Deprecate fork being the multiprocessing default.
gpshead Dec 30, 2022
df83fba
address CI test failures?
gpshead Dec 31, 2022
ec1e868
the new warning needs no pickle name mapping
gpshead Dec 31, 2022
a1064de
avoid DeprecationWarnings vs -Werror
gpshead Dec 31, 2022
223b748
prefer forkserver over fork for concurrent.futures
gpshead Dec 31, 2022
fc64626
explicitly use spawn for simple process launchers.
gpshead Dec 31, 2022
e45fab6
warn from concurrent.futures, reword things.
gpshead Dec 31, 2022
29764a2
avoid double warning in futures
gpshead Dec 31, 2022
c52b9db
Cleanup messages, test futures warning.
gpshead Dec 31, 2022
4c8cc34
cleanup warn stacklevel logic
gpshead Dec 31, 2022
7179684
Document all the things!
gpshead Dec 31, 2022
f7e3161
Have all doctests use 'spawn'.
gpshead Jan 1, 2023
9947860
Correct warning stacklevel for Manager.
gpshead Jan 1, 2023
5834f2d
more doctest cleanup.
gpshead Jan 1, 2023
7d48e86
NEWS entry.
gpshead Jan 1, 2023
28c0cfc
docs: add the implicit i
gpshead Jan 10, 2023
2820bb8
Merge branch 'main' into multiprocessing/deprecate-fork-default
gpshead Jan 28, 2023
4c16205
Use skip_file_prefixes.
gpshead Jan 28, 2023
7d84a72
use the modern warnings API, doc updates.
gpshead Jan 28, 2023
8b2029e
documentation cleanup
gpshead Jan 28, 2023
846e9a0
Remove an unused variable.
gpshead Feb 1, 2023
7078986
doc typo fix, unnecessary method change revert.
gpshead Feb 1, 2023
e3e3b3c
Add What's New entries.
gpshead Feb 2, 2023
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Cleanup messages, test futures warning.
  • Loading branch information
@gpshead
gpshead committed Dec 31, 2022
commit c52b9dba4c06e7bc51f62fe44bbe0de243a30b8f
19 changes: 8 additions & 11 deletions Lib/concurrent/futures/process.py
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Original file line number Diff line number Diff line change
Expand Up @@ -650,19 +650,16 @@ def __init__(self, max_workers=None, mp_context=None,
mp_context = mp.get_context("spawn")
else:
mp_context = mp.get_context()
# getattr(...)() instead of .get_start_method() as the docs imply that
# this method is not required. Hokey! But if someone passed us an odd
# duck, we just skip our introspection and warning.
if (getattr(mp_context, "get_start_method", lambda: None)() == "fork"
and mp_context == mp.context._default_context._default_context):
if (mp_context.get_start_method() == "fork" and
mp_context == mp.context._default_context._default_context):
import warnings
warnings.warn(
"The multiprocessing 'fork' start method will change "
"away from 'fork' in Python >= 3.14, per GH-84559. "
"concurrent.futures.process is built upon multiprocessing. "
"If your application requires continued use of 'fork', "
"pass a mp_context= parameter created with the start method "
"explicitly specified.",
"The default multiprocessing start method will change "
"away from 'fork' in Python >= 3.14, per GH-84559. "
"ProcessPoolExecutor uses multiprocessing. "
"If your application requires 'fork', explicitly specify "
"that by passing a mp_context= parameter. "
"The safest start method is 'spawn'.",
category=mp.context.DefaultForkDeprecationWarning,
stacklevel=2,
)
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10 changes: 5 additions & 5 deletions Lib/multiprocessing/context.py
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Expand Up @@ -289,11 +289,11 @@ class _DeprecatedForkProcess(ForkProcess):
def _warn(stacklevel):
import warnings
warnings.warn(
"The multiprocessing 'fork' start method will change "
"change away from 'fork' in Python >= 3.14, per GH-84559. "
"Use a multiprocessing.get_context(X) context or "
"call multiprocessing.set_start_method(X) to explicitly "
"specify your application's need if you really want 'fork'.",
"The default multiprocessing start method will change "
"away from 'fork' in Python >= 3.14, per GH-84559. "
"Use multiprocessing.get_context(X) or .set_start_method(X) to "
"explicitly specify it when your application requires 'fork'. "
"The safest start method is 'spawn'.",
category=DefaultForkDeprecationWarning,
stacklevel=stacklevel,
)
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19 changes: 19 additions & 0 deletions Lib/test/test_concurrent_futures.py
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Expand Up @@ -18,6 +18,7 @@
import threading
import time
import unittest
import warnings
import weakref
from pickle import PicklingError

Expand Down Expand Up @@ -571,6 +572,24 @@ def test_shutdown_no_wait(self):
assert all([r == abs(v) for r, v in zip(res, range(-5, 5))])


@unittest.skipIf(mp.get_all_start_methods()[0] != "fork", "non-fork default.")
class ProcessPoolExecutorDefaultForkWarning(unittest.TestCase):
def test_fork_default_warns(self):
with self.assertWarns(mp.context.DefaultForkDeprecationWarning):
with futures.ProcessPoolExecutor(2):
pass

def test_explicit_fork_does_not_warn(self):
with warnings.catch_warnings(record=True) as ws:
warnings.simplefilter("ignore")
warnings.filterwarnings(
'always', category=mp.context.DefaultForkDeprecationWarning)
ctx = mp.get_context("fork") # Non-default fork context.
with futures.ProcessPoolExecutor(2, mp_context=ctx):
pass
self.assertEqual(len(ws), 0, msg=[str(x) for x in ws])


create_executor_tests(ProcessPoolShutdownTest,
executor_mixins=(ProcessPoolForkMixin,
ProcessPoolForkserverMixin,
Expand Down