gh-95804: Respect MemoryHandler.flushOnClose in logging shutdown. (GH-95857)

Lib/logging/__init__.py

@@ -2245,7 +2245,11 @@ def shutdown(handlerList=_handlerList):
             if h:
                 try:
                     h.acquire()
-                    h.flush()
+                    # MemoryHandlers might not want to be flushed on close,
+                    # but circular imports prevent us scoping this to just
+                    # those handlers.  hence the default to True.
+                    if getattr(h, 'flushOnClose', True):
+                        h.flush()
                     h.close()
                 except (OSError, ValueError):
                     # Ignore errors which might be caused

Lib/test/test_logging.py

@@ -1225,6 +1225,35 @@ class MemoryHandlerTest(BaseTest):
         # assert that no new lines have been added
         self.assert_log_lines(lines)  # no change
 
+    def test_shutdown_flush_on_close(self):
+        """
+        Test that the flush-on-close configuration is respected by the
+        shutdown method.
+        """
+        self.mem_logger.debug(self.next_message())
+        self.assert_log_lines([])
+        self.mem_logger.info(self.next_message())
+        self.assert_log_lines([])
+        # Default behaviour is to flush on close. Check that it happens.
+        logging.shutdown(handlerList=[logging.weakref.ref(self.mem_hdlr)])
+        lines = [
+            ('DEBUG', '1'),
+            ('INFO', '2'),
+        ]
+        self.assert_log_lines(lines)
+        # Now configure for flushing not to be done on close.
+        self.mem_hdlr = logging.handlers.MemoryHandler(10, logging.WARNING,
+                                                       self.root_hdlr,
+                                                       False)
+        self.mem_logger.addHandler(self.mem_hdlr)
+        self.mem_logger.debug(self.next_message())
+        self.assert_log_lines(lines)  # no change
+        self.mem_logger.info(self.next_message())
+        self.assert_log_lines(lines)  # no change
+        # assert that no new lines have been added after shutdown
+        logging.shutdown(handlerList=[logging.weakref.ref(self.mem_hdlr)])
+        self.assert_log_lines(lines) # no change
+
     @threading_helper.requires_working_threading()
     def test_race_between_set_target_and_flush(self):
         class MockRaceConditionHandler:

Misc/ACKS

@@ -198,6 +198,7 @@ Gawain Bolton
 Carl Friedrich Bolz-Tereick
 Forest Bond
 Gregory Bond
+David Bonner
 Angelin Booz
 Médéric Boquien
 Matias Bordese

Misc/NEWS.d/next/Library/2022-08-10-11-54-04.gh-issue-95804.i5FCFK.rst

@@ -0,0 +1,2 @@
+Fix ``logging`` shutdown handler so it respects
+``MemoryHandler.flushOnClose``.