From: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>
Date: Sat, 30 Nov 2024 09:05:46 +0000 (+0100)
Subject: [3.12] gh-88110: Clear concurrent.futures.thread._threads_queues after fork to avoid... 
X-Git-Tag: v3.12.8~18
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=7c7ed49b518f986806edf2f3d67198cb516b7a98;p=thirdparty%2FPython%2Fcpython.git

[3.12] gh-88110: Clear concurrent.futures.thread._threads_queues after fork to avoid joining parent process' threads (GH-126098) (GH-127164)

Threads are gone after fork, so clear the queues too. Otherwise the
child process (here created via multiprocessing.Process) crashes on
interpreter exit.

(cherry picked from commit 1848ce61f349533ae5892a8c24c2e0e3c364fc8a)

Co-authored-by: Andrei Bodrov <Drino@users.noreply.github.com>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
---

diff --git a/Lib/concurrent/futures/thread.py b/Lib/concurrent/futures/thread.py
index 3b3a36a50933..61dbff8a485b 100644
--- a/Lib/concurrent/futures/thread.py
+++ b/Lib/concurrent/futures/thread.py
@@ -41,6 +41,7 @@ if hasattr(os, 'register_at_fork'):
     os.register_at_fork(before=_global_shutdown_lock.acquire,
                         after_in_child=_global_shutdown_lock._at_fork_reinit,
                         after_in_parent=_global_shutdown_lock.release)
+    os.register_at_fork(after_in_child=_threads_queues.clear)
 
 
 class _WorkItem:
diff --git a/Lib/test/test_concurrent_futures/test_thread_pool.py b/Lib/test/test_concurrent_futures/test_thread_pool.py
index 812f989d8f3a..6e4a4b7caff4 100644
--- a/Lib/test/test_concurrent_futures/test_thread_pool.py
+++ b/Lib/test/test_concurrent_futures/test_thread_pool.py
@@ -64,6 +64,25 @@ class ThreadPoolExecutorTest(ThreadPoolMixin, ExecutorTest, BaseTestCase):
                 with futures.ProcessPoolExecutor(1, mp_context=mp.get_context('fork')) as workers:
                     workers.submit(tuple)
 
+    @support.requires_fork()
+    @unittest.skipUnless(hasattr(os, 'register_at_fork'), 'need os.register_at_fork')
+    def test_process_fork_from_a_threadpool(self):
+        # bpo-43944: clear concurrent.futures.thread._threads_queues after fork,
+        # otherwise child process will try to join parent thread
+        def fork_process_and_return_exitcode():
+            # Ignore the warning about fork with threads.
+            with self.assertWarnsRegex(DeprecationWarning,
+                                       r"use of fork\(\) may lead to deadlocks in the child"):
+                p = mp.get_context('fork').Process(target=lambda: 1)
+                p.start()
+            p.join()
+            return p.exitcode
+
+        with futures.ThreadPoolExecutor(1) as pool:
+            process_exitcode = pool.submit(fork_process_and_return_exitcode).result()
+
+        self.assertEqual(process_exitcode, 0)
+
     def test_executor_map_current_future_cancel(self):
         stop_event = threading.Event()
         log = []
diff --git a/Misc/NEWS.d/next/Library/2023-02-15-23-54-42.gh-issue-88110.KU6erv.rst b/Misc/NEWS.d/next/Library/2023-02-15-23-54-42.gh-issue-88110.KU6erv.rst
new file mode 100644
index 000000000000..42a83edc3ba6
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-02-15-23-54-42.gh-issue-88110.KU6erv.rst
@@ -0,0 +1,2 @@
+Fixed :class:`multiprocessing.Process` reporting a ``.exitcode`` of 1 even on success when
+using the ``"fork"`` start method while using a :class:`concurrent.futures.ThreadPoolExecutor`.