[3.10] bpo-42378: fixed log truncation on logging shutdown (GH-27310) (GH-30468)

Co-authored-by: andrei kulakov <andrei.avk@gmail.com>

Lib/logging/__init__.py

@@ -878,6 +878,7 @@ 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()
@@ -996,6 +997,7 @@ 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:
@@ -1184,6 +1186,8 @@ 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()
@@ -1203,10 +1207,15 @@ 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)