[3.12] gh-88110: Clear concurrent.futures.thread._threads_queues after fork to avoid...

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 3b3a36a5093336cfd9491d3cf269d49fdac9dd63..61dbff8a485bcdf38ad095d50ed0eeb705615a97 100644 (file)
--- 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 812f989d8f3ad2deae2bbd107f9c95acc17dd602..6e4a4b7caff48176ec2edfc6c725409c474ba559 100644 (file)
--- 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 (file)
index 0000000..42a83ed
--- /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`.