gh-127567: Avoid forceful shutting down of handlers during reconfiguration

Lib/logging/config.py

@@ -285,9 +285,20 @@ def _install_loggers(cp, handlers, disable_existing):
 
 
 def _clearExistingHandlers():
-    """Clear and close existing handlers"""
+    """Clear and close handlers that are no longer in use."""
+    active_handlers = {
+        handler
+        for logger in logging.Logger.manager.loggerDict.values()
+        if isinstance(logger, logging.Logger)
+        for handler in logger.handlers
+    }
+
+    for handler_ref in list(logging._handlers.values()):
+        handler = handler_ref() if callable(handler_ref) else handler_ref
+        if handler and handler not in active_handlers:
+            handler.close()
+
     logging._handlers.clear()
-    logging.shutdown(logging._handlerList[:])
     del logging._handlerList[:]
 
 

Lib/test/test_logging.py

@@ -3554,6 +3554,27 @@ def test_config15_ok(self):
         handler = logging.root.handlers[0]
         self.addCleanup(closeFileHandler, handler, fn)
 
+    def test_disable_existing_loggers(self):
+        fn = make_temp_file(".log", "test_logging-disable-existing-loggers-")
+        file_handler = logging.FileHandler(fn, mode="w")
+        file_handler.setFormatter(logging.Formatter("%(message)s"))
+        root_logger = logging.getLogger()
+        root_logger.addHandler(file_handler)
+
+        config = {"version": 1, "disable_existing_loggers": False}
+
+        # we have disable_existing_loggers=False,
+        # so, all handlers should continue working
+        self.apply_config(config)
+
+        msg = "test message"
+        logging.warning(msg)
+        file_handler.close()
+        with open(fn, encoding='utf-8') as f:
+            data = f.read().strip()
+        os.remove(fn)
+        self.assertEqual(data, msg)
+
     def test_config16_ok(self):
         self.apply_config(self.config16)
         h = logging._handlers['hand1']

Misc/NEWS.d/next/Library/2024-12-06-16-40-27.gh-issue-127567.uuPayH.rst

@@ -0,0 +1 @@
+Avoid shutting down handlers during reconfiguration