python · miss-islington · Nov 19, 2019 · Nov 19, 2019
diff --git a/Lib/multiprocessing/process.py b/Lib/multiprocessing/process.py
@@ -301,6 +301,8 @@ def _bootstrap(self, parent_sentinel=None):
            _current_process = self
            _parent_process = _ParentProcess(
                self._parent_name, self._parent_pid, parent_sentinel)
+            if threading._HAVE_THREAD_NATIVE_ID:
+                threading.main_thread()._set_native_id()
            try:
                util._finalizer_registry.clear()
                util._run_after_forkers()

diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
@@ -367,6 +367,28 @@ def test_process(self):
        self.assertNotIn(p, self.active_children())
        close_queue(q)

+    @unittest.skipUnless(threading._HAVE_THREAD_NATIVE_ID, "needs native_id")
+    def test_process_mainthread_native_id(self):
+        if self.TYPE == 'threads':
+            self.skipTest('test not appropriate for {}'.format(self.TYPE))
+
+        current_mainthread_native_id = threading.main_thread().native_id
+
+        q = self.Queue(1)
+        p = self.Process(target=self._test_process_mainthread_native_id, args=(q,))
+        p.start()
+
+        child_mainthread_native_id = q.get()
+        p.join()
+        close_queue(q)
+
+        self.assertNotEqual(current_mainthread_native_id, child_mainthread_native_id)
+
+    @classmethod
+    def _test_process_mainthread_native_id(cls, q):
+        mainthread_native_id = threading.main_thread().native_id
+        q.put(mainthread_native_id)
+
    @classmethod
    def _sleep_some(cls):
        time.sleep(100)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-11-08-00-36-10.bpo-38707.SZL036.rst b/Misc/NEWS.d/next/Core and Builtins/2019-11-08-00-36-10.bpo-38707.SZL036.rst
@@ -0,0 +1 @@
+``MainThread.native_id`` is now correctly reset in child processes spawned using :class:`multiprocessing.Process`, instead of retaining the parent's value.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		``MainThread.native_id`` is now correctly reset in child processes spawned using :class:`multiprocessing.Process`, instead of retaining the parent's value.