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gh-134381: Fix RuntimeError when starting not-yet started Thread after fork (gh-134514)
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Lib/test/_test_multiprocessing.py

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@@ -6844,6 +6844,28 @@ def f(x): return x*x
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self.assertEqual("332833500", out.decode('utf-8').strip())
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self.assertFalse(err, msg=err.decode('utf-8'))
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def test_forked_thread_not_started(self):
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# gh-134381: Ensure that a thread that has not been started yet in
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# the parent process can be started within a forked child process.
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if multiprocessing.get_start_method() != "fork":
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self.skipTest("fork specific test")
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q = multiprocessing.Queue()
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t = threading.Thread(target=lambda: q.put("done"), daemon=True)
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def child():
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t.start()
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t.join()
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p = multiprocessing.Process(target=child)
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p.start()
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p.join(support.SHORT_TIMEOUT)
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self.assertEqual(p.exitcode, 0)
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self.assertEqual(q.get_nowait(), "done")
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close_queue(q)
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#
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# Mixins
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Fix :exc:`RuntimeError` when using a not-started :class:`threading.Thread` after calling :func:`os.fork`

Modules/_threadmodule.c

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@@ -296,6 +296,12 @@ _PyThread_AfterFork(struct _pythread_runtime_state *state)
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continue;
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}
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// Keep handles for threads that have not been started yet. They are
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// safe to start in the child process.
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if (handle->state == THREAD_HANDLE_NOT_STARTED) {
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continue;
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}
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// Mark all threads as done. Any attempts to join or detach the
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// underlying OS thread (if any) could crash. We are the only thread;
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// it's safe to set this non-atomically.

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