pythongh-127567: Avoid shuting down 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 +3554,32 @@ def test_config15_ok(self):
         handler = logging.root.handlers[0]
         self.addCleanup(closeFileHandler, handler, fn)
 
+    def test_clear_existing_handlers_preserves_active_handlers(self):
+        """Test that active handlers are preserved and unused handlers are closed."""
+
+        with self.check_no_resource_warning():
+            fn = make_temp_file(".log", "test_logging-clear-")
+            config = {
+                "version": 1,
+                "handlers": {
+                    "file": {
+                        "class": "logging.FileHandler",
+                        "filename": fn,
+                        "encoding": "utf-8",
+                    }
+                },
+                "root": {
+                    "handlers": ["file"]
+                }
+            }
+
+            self.apply_config(config)
+            self.apply_config(config)
+
+            handler = logging.root.handlers[0]
+            self.assertFalse(handler._closed, "Handler should not be closed")
+            self.addCleanup(closeFileHandler, handler, fn)
+
     def test_config16_ok(self):
         self.apply_config(self.config16)
         h = logging._handlers['hand1']