fix: prevent once handlers from refiring on epoch termination

ignite/engine/engine.py

@@ -325,6 +325,9 @@ def execute_something():
             return RemovableEventHandle(event_name, handler, self)
         if isinstance(event_name, CallableEventWithFilter) and event_name.filter is not None:
             event_filter = event_name.filter
+            once = getattr(event_filter, "_once", None)
+            if once is not None:
+                event_filter = Events.once_event_filter(list(once))
             handler = self._handler_wrapper(handler, event_name, event_filter)
 
         self._assert_allowed_event(event_name)

ignite/engine/events.py

@@ -140,12 +140,15 @@ def wrapper(engine: "Engine", event: int) -> bool:
     @staticmethod
     def once_event_filter(once: list) -> Callable:
         """A wrapper for once event filter."""
+        remaining = set(once)
 
         def wrapper(engine: "Engine", event: int) -> bool:
-            if event in once:
+            if event in remaining:
+                remaining.remove(event)
                 return True
             return False
 
+        wrapper._once = tuple(once)  # type: ignore[attr-defined]
         return wrapper
 
     @staticmethod

tests/ignite/engine/test_engine.py

@@ -395,6 +395,7 @@ def check_previous_events2():
 
             epoch_completed_events = [e for e in engine.called_events if e[2] == Events.EPOCH_COMPLETED.name]
             assert len(epoch_completed_events) == max_epochs - skip_epoch_completed
+            assert call_count == 1
 
     @pytest.mark.parametrize("data", [None, "mock_data_loader"])
     def test_iteration_events_are_fired(self, data):