bpo-42378: fixed log truncation on logging shutdown (GH-27310)

Automerge-Triggered-By: GH:vsajip

1 files changed, 11 insertions, 2 deletions

diff --git a/Lib/logging/__init__.py b/Lib/logging/__init__.py
index 3538f06..e49e0d0 100644
--- a/Lib/logging/__init__.py
+++ b/Lib/logging/__init__.py
@@ -882,6 +882,7 @@ class Handler(Filterer):
         self._name = None
         self.level = _checkLevel(level)
         self.formatter = None
+        self._closed = False
         # Add the handler to the global _handlerList (for cleanup on shutdown)
         _addHandlerRef(self)
         self.createLock()
@@ -1000,6 +1001,7 @@ class Handler(Filterer):
         #get the module data lock, as we're updating a shared structure.
         _acquireLock()
         try:    #unlikely to raise an exception, but you never know...
+            self._closed = True
             if self._name and self._name in _handlers:
                 del _handlers[self._name]
         finally:
@@ -1188,6 +1190,8 @@ class FileHandler(StreamHandler):
             finally:
                 # Issue #19523: call unconditionally to
                 # prevent a handler leak when delay is set
+                # Also see Issue #42378: we also rely on
+                # self._closed being set to True there
                 StreamHandler.close(self)
         finally:
             self.release()
@@ -1207,10 +1211,15 @@ class FileHandler(StreamHandler):
 
         If the stream was not opened because 'delay' was specified in the
         constructor, open it before calling the superclass's emit.
+
+        If stream is not open, current mode is 'w' and `_closed=True`, record
+        will not be emitted (see Issue #42378).
         """
         if self.stream is None:
-            self.stream = self._open()
-        StreamHandler.emit(self, record)
+            if self.mode != 'w' or not self._closed:
+                self.stream = self._open()
+        if self.stream:
+            StreamHandler.emit(self, record)
 
     def __repr__(self):
         level = getLevelName(self.level)