Enhance comment message, recreate test scenario in _test_multiprocessing

Author: zangjiucheng

Lib/test/_test_multiprocessing.py

@@ -6844,6 +6844,28 @@ def f(x): return x*x
         self.assertEqual("332833500", out.decode('utf-8').strip())
         self.assertFalse(err, msg=err.decode('utf-8'))
 
+    @support.requires_fork()
+    def test_forked_not_started(self):
+        # gh-134381
+        # Ensure that a forked parent process, which has not been started yet,
+        # can be initiated within the child process.
+
+        ctx = multiprocessing.get_context("fork")   # local “fork” cont
+        q = ctx.Queue()
+        t = threading.Thread(target=lambda: q.put("done"), daemon=True)
+
+        def child():
+            t.start()
+            t.join()
+
+        p = ctx.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

Lib/test/test_thread.py

@@ -439,21 +439,6 @@ def fork_thread(read_fd, write_fd):
         self.assertIsNotNone(pid)
         support.wait_process(pid, exitcode=0)
 
-    @support.requires_fork()
-    @threading_helper.reap_threads
-    def test_forked_not_started(self):
-        handle = thread._ThreadHandle()
-        pid = os.fork()
-        if pid == 0:
-            # child process
-            try:
-                self.assertTrue(handle.is_alive())
-                self.assertFalse(handle.is_done())
-            finally:
-                os._exit(0)
-        else:
-            support.wait_process(pid, exitcode=0)
-
     def tearDown(self):
         try:
             os.close(self.read_fd)

Modules/_threadmodule.c

@@ -296,7 +296,8 @@ _PyThread_AfterFork(struct _pythread_runtime_state *state)
             continue;
         }
 
-        // keep not_start handles – they are safe to start in the child
+        // 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;
         }