Handle logger flushing already closed file (#686)

This is a partial cherry-pick of
saltstack/salt@9683260

salt/_logging/handlers.py

@@ -95,6 +95,9 @@ def __init__(self, stream, max_queue_size=10000):
         super().__init__(stream)
         self.__messages = deque(maxlen=max_queue_size)
         self.__emitting = False
+        import traceback
+
+        self.stack = "".join(traceback.format_stack())
 
     def handle(self, record):
         self.acquire()
@@ -116,6 +119,7 @@ def flush(self):
                 super().handle(record)
             finally:
                 self.__emitting = False
+        # This will raise a ValueError if the file handle has been closed.
         super().flush()
 
     def sync_with_handlers(self, handlers=()):

salt/_logging/impl.py

@@ -488,7 +488,15 @@ def setup_temp_handler(log_level=None):
             break
     else:
         handler = DeferredStreamHandler(sys.stderr)
-        atexit.register(handler.flush)
+
+        def tryflush():
+            try:
+                handler.flush()
+            except ValueError:
+                # File handle has already been closed.
+                pass
+
+        atexit.register(tryflush)
     handler.setLevel(log_level)
 
     # Set the default temporary console formatter config