From c5ea06e5bbffc9e1b8d69d5f4c9fc707f0bbe9ae Mon Sep 17 00:00:00 2001 From: "Jiucheng(Oliver)" Date: Fri, 23 May 2025 15:22:14 -0400 Subject: [PATCH] gh-134381: Fix RuntimeError when starting not-yet started Thread after fork (gh-134514) (cherry picked from commit 9a2346df861f26d5f8d054ad2f9c37134dee3822) Co-authored-by: Jiucheng(Oliver) --- Lib/test/_test_multiprocessing.py | 22 +++++++++++++++++++ ...-05-22-14-48-19.gh-issue-134381.2BXhth.rst | 1 + Modules/_threadmodule.c | 6 +++++ 3 files changed, 29 insertions(+) create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2025-05-22-14-48-19.gh-issue-134381.2BXhth.rst diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py index 9e3330e40ffaab..0b8de96f1b0c96 100644 --- a/Lib/test/_test_multiprocessing.py +++ b/Lib/test/_test_multiprocessing.py @@ -6494,6 +6494,28 @@ def f(x): return x*x self.assertEqual("332833500", out.decode('utf-8').strip()) self.assertFalse(err, msg=err.decode('utf-8')) + def test_forked_thread_not_started(self): + # gh-134381: Ensure that a thread that has not been started yet in + # the parent process can be started within a forked child process. + + if multiprocessing.get_start_method() != "fork": + self.skipTest("fork specific test") + + q = multiprocessing.Queue() + t = threading.Thread(target=lambda: q.put("done"), daemon=True) + + def child(): + t.start() + t.join() + + p = multiprocessing.Process(target=child) + p.start() + p.join(support.SHORT_TIMEOUT) + + self.assertEqual(p.exitcode, 0) + self.assertEqual(q.get_nowait(), "done") + close_queue(q) + # # Mixins diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-05-22-14-48-19.gh-issue-134381.2BXhth.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-05-22-14-48-19.gh-issue-134381.2BXhth.rst new file mode 100644 index 00000000000000..aa8900296ae2fc --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-05-22-14-48-19.gh-issue-134381.2BXhth.rst @@ -0,0 +1 @@ +Fix :exc:`RuntimeError` when using a not-started :class:`threading.Thread` after calling :func:`os.fork` diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c index 2853f3d26773d0..52bb45f1891ac3 100644 --- a/Modules/_threadmodule.c +++ b/Modules/_threadmodule.c @@ -262,6 +262,12 @@ _PyThread_AfterFork(struct _pythread_runtime_state *state) continue; } + // Keep handles for threads that have not been started yet. They are + // safe to start in the child process. + if (handle->state == THREAD_HANDLE_NOT_STARTED) { + continue; + } + // Mark all threads as done. Any attempts to join or detach the // underlying OS thread (if any) could crash. We are the only thread; // it's safe to set this non-atomically. pFad - Phonifier reborn

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