python · serhiy-storchaka · May 20, 2025 · May 20, 2025
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
@@ -1352,6 +1352,34 @@ def do_flush(*args, **kwargs):
        ''')
        assert_python_ok("-c", script)

+    @skip_unless_reliable_fork
+    def test_native_id_after_fork(self):
+        script = """if True:
+            import threading
+            import os
+            from test import support
+
+            parent_thread_native_id = threading.current_thread().native_id
+            print(parent_thread_native_id, flush=True)
+            assert parent_thread_native_id == threading.get_native_id()
+            childpid = os.fork()
+            if childpid == 0:
+                print(threading.current_thread().native_id, flush=True)
+                assert threading.current_thread().native_id == threading.get_native_id()
+            else:
+                try:
+                    assert parent_thread_native_id == threading.current_thread().native_id
+                    assert parent_thread_native_id == threading.get_native_id()
+                finally:
+                    support.wait_process(childpid, exitcode=0)
+            """
+        rc, out, err = assert_python_ok('-c', script)
+        self.assertEqual(rc, 0)
+        self.assertEqual(err, b"")
+        native_ids = out.strip().splitlines()
+        self.assertEqual(len(native_ids), 2)
+        self.assertNotEqual(native_ids[0], native_ids[1])
+
 class ThreadJoinOnShutdown(BaseTestCase):

    def _run_and_join(self, script):

diff --git a/Lib/threading.py b/Lib/threading.py
@@ -951,6 +951,8 @@ def _after_fork(self, new_ident=None):
            # This thread is alive.
            self._ident = new_ident
            assert self._os_thread_handle.ident == new_ident
+            if _HAVE_THREAD_NATIVE_ID:
+                self._set_native_id()
        else:
            # Otherwise, the thread is dead, Jim.  _PyThread_AfterFork()
            # already marked our handle done.

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-04-19-17-16-46.gh-issue-132542.7T_TY_.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-04-19-17-16-46.gh-issue-132542.7T_TY_.rst
@@ -0,0 +1,2 @@
+Update :attr:`Thread.native_id <threading.Thread.native_id>` after
+:manpage:`fork(2)` to ensure accuracy. Patch by Noam Cohen.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Update :attr:`Thread.native_id <threading.Thread.native_id>` after
		:manpage:`fork(2)` to ensure accuracy. Patch by Noam Cohen.