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gh-100228: Warn from os.fork() if other threads exist. (#100229)

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Not comprehensive, best effort warning. There are cases when threads exist on some platforms that this code cannot detect. macOS when API permissions allow and Linux with a readable /proc procfs present are the currently supported cases where a warning should show up reliably.

Starting with a DeprecationWarning for now, it is less disruptive than something like RuntimeWarning and most likely to only be seen in people's CI tests - a good place to start with this messaging.
This commit is contained in:
Gregory P. Smith 2022-12-29 14:41:39 -08:00 • committed by GitHub
parent 2df82db485
commit 894f2c3c16
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12 changed files with 283 additions and 66 deletions
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110
Lib/test/test_threading.py
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@ -20,6 +20,7 @@
import signal
import textwrap
import traceback
import warnings
from unittest import mock
from test import lock_tests
@ -563,7 +564,7 @@ def test_dummy_thread_after_fork(self):
# Issue #14308: a dummy thread in the active list doesn't mess up
# the after-fork mechanism.
code = """if 1:
import _thread, threading, os, time
import _thread, threading, os, time, warnings
def background_thread(evt):
# Creates and registers the _DummyThread instance
@ -575,11 +576,16 @@ def background_thread(evt):
_thread.start_new_thread(background_thread, (evt,))
evt.wait()
assert threading.active_count() == 2, threading.active_count()
if os.fork() == 0:
assert threading.active_count() == 1, threading.active_count()
os._exit(0)
else:
os.wait()
with warnings.catch_warnings(record=True) as ws:
warnings.filterwarnings(
"always", category=DeprecationWarning)
if os.fork() == 0:
assert threading.active_count() == 1, threading.active_count()
os._exit(0)
else:
assert ws[0].category == DeprecationWarning, ws[0]
assert 'fork' in str(ws[0].message), ws[0]
os.wait()
"""
_, out, err = assert_python_ok("-c", code)
self.assertEqual(out, b'')
@ -598,13 +604,15 @@ def test_is_alive_after_fork(self):
for i in range(20):
t = threading.Thread(target=lambda: None)
t.start()
pid = os.fork()
if pid == 0:
os._exit(11 if t.is_alive() else 10)
else:
t.join()
# Ignore the warning about fork with threads.
with warnings.catch_warnings(category=DeprecationWarning,
action="ignore"):
if (pid := os.fork()) == 0:
os._exit(11 if t.is_alive() else 10)
else:
t.join()
support.wait_process(pid, exitcode=10)
support.wait_process(pid, exitcode=10)
def test_main_thread(self):
main = threading.main_thread()
@ -645,21 +653,26 @@ def test_main_thread_after_fork(self):
@unittest.skipUnless(hasattr(os, 'waitpid'), "test needs os.waitpid()")
def test_main_thread_after_fork_from_nonmain_thread(self):
code = """if 1:
import os, threading, sys
import os, threading, sys, warnings
from test import support
def func():
pid = os.fork()
if pid == 0:
main = threading.main_thread()
print(main.name)
print(main.ident == threading.current_thread().ident)
print(main.ident == threading.get_ident())
# stdout is fully buffered because not a tty,
# we have to flush before exit.
sys.stdout.flush()
else:
support.wait_process(pid, exitcode=0)
with warnings.catch_warnings(record=True) as ws:
warnings.filterwarnings(
"always", category=DeprecationWarning)
pid = os.fork()
if pid == 0:
main = threading.main_thread()
print(main.name)
print(main.ident == threading.current_thread().ident)
print(main.ident == threading.get_ident())
# stdout is fully buffered because not a tty,
# we have to flush before exit.
sys.stdout.flush()
else:
assert ws[0].category == DeprecationWarning, ws[0]
assert 'fork' in str(ws[0].message), ws[0]
support.wait_process(pid, exitcode=0)
th = threading.Thread(target=func)
th.start()
@ -667,7 +680,7 @@ def func():
"""
_, out, err = assert_python_ok("-c", code)
data = out.decode().replace('\r', '')
self.assertEqual(err, b"")
self.assertEqual(err.decode('utf-8'), "")
self.assertEqual(data, "Thread-1 (func)\nTrue\nTrue\n")
def test_main_thread_during_shutdown(self):
@ -1173,15 +1186,18 @@ def do_fork_and_wait():
else:
os._exit(50)
# start a bunch of threads that will fork() child processes
threads = []
for i in range(16):
t = threading.Thread(target=do_fork_and_wait)
threads.append(t)
t.start()
# Ignore the warning about fork with threads.
with warnings.catch_warnings(category=DeprecationWarning,
action="ignore"):
# start a bunch of threads that will fork() child processes
threads = []
for i in range(16):
t = threading.Thread(target=do_fork_and_wait)
threads.append(t)
t.start()
for t in threads:
t.join()
for t in threads:
t.join()
@support.requires_fork()
def test_clear_threads_states_after_fork(self):
@ -1194,18 +1210,22 @@ def test_clear_threads_states_after_fork(self):
threads.append(t)
t.start()
pid = os.fork()
if pid == 0:
# check that threads states have been cleared
if len(sys._current_frames()) == 1:
os._exit(51)
else:
os._exit(52)
else:
support.wait_process(pid, exitcode=51)
for t in threads:
t.join()
try:
# Ignore the warning about fork with threads.
with warnings.catch_warnings(category=DeprecationWarning,
action="ignore"):
pid = os.fork()
if pid == 0:
# check that threads states have been cleared
if len(sys._current_frames()) == 1:
os._exit(51)
else:
os._exit(52)
else:
support.wait_process(pid, exitcode=51)
finally:
for t in threads:
t.join()
class SubinterpThreadingTests(BaseTestCase):