gh-59705: Set OS thread name when Thread.name is changed (#127702)

Co-authored-by: Petr Viktorin <encukou@gmail.com>

2 files changed, 30 insertions, 5 deletions

diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index d05161f..3e164a1 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -2164,6 +2164,25 @@ class MiscTestCase(unittest.TestCase):
                 self.assertEqual(work_name, expected,
                                  f"{len(work_name)=} and {len(expected)=}")
 
+    @unittest.skipUnless(hasattr(_thread, 'set_name'), "missing _thread.set_name")
+    @unittest.skipUnless(hasattr(_thread, '_get_name'), "missing _thread._get_name")
+    def test_change_name(self):
+        # Change the name of a thread while the thread is running
+
+        name1 = None
+        name2 = None
+        def work():
+            nonlocal name1, name2
+            name1 = _thread._get_name()
+            threading.current_thread().name = "new name"
+            name2 = _thread._get_name()
+
+        thread = threading.Thread(target=work, name="name")
+        thread.start()
+        thread.join()
+        self.assertEqual(name1, "name")
+        self.assertEqual(name2, "new name")
+
 
 class InterruptMainTests(unittest.TestCase):
     def check_interrupt_main_with_signal_handler(self, signum):
diff --git a/Lib/threading.py b/Lib/threading.py
index 3abd22a..78e5911 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -1026,16 +1026,20 @@ class Thread:
         def _set_native_id(self):
             self._native_id = get_native_id()
 
+    def _set_os_name(self):
+        if _set_name is None or not self._name:
+            return
+        try:
+            _set_name(self._name)
+        except OSError:
+            pass
+
     def _bootstrap_inner(self):
         try:
             self._set_ident()
             if _HAVE_THREAD_NATIVE_ID:
                 self._set_native_id()
-            if _set_name is not None and self._name:
-                try:
-                    _set_name(self._name)
-                except OSError:
-                    pass
+            self._set_os_name()
             self._started.set()
             with _active_limbo_lock:
                 _active[self._ident] = self
@@ -1115,6 +1119,8 @@ class Thread:
     def name(self, name):
         assert self._initialized, "Thread.__init__() not called"
         self._name = str(name)
+        if get_ident() == self._ident:
+            self._set_os_name()
 
     @property
     def ident(self):