fix: add exception handling to _run_handle and fix mypy errors

Address PR review comments:
- Wrap _run_handle in try/except to match CPython Handle._run()
  behavior, preventing unhandled exceptions from crashing the event loop
- Fix mypy no-any-return in signal.py params_from_payload
- Fix mypy attr-defined errors for Handle private attributes
- Update tests to verify exceptions are logged rather than propagated

Signed-off-by: Tim Li <ltim@uber.com>
Made-with: Cursor

Author: timl3136

cadence/_internal/workflow/deterministic_event_loop.py

@@ -169,7 +169,22 @@ def _run_once(self) -> None:
 
     @staticmethod
     def _run_handle(handle: events.Handle) -> None:
-        handle._context.run(handle._callback, *handle._args)
+        try:
+            ctx = handle._context  # type: ignore[attr-defined]
+            cb = handle._callback  # type: ignore[attr-defined]
+            args = handle._args  # type: ignore[attr-defined]
+            if ctx is not None:
+                ctx.run(cb, *args)
+            else:
+                cb(*args)
+        except (SystemExit, KeyboardInterrupt):
+            raise
+        except BaseException as exc:
+            handle._loop.call_exception_handler({  # type: ignore[attr-defined]
+                'message': 'Exception in callback %r' % handle,
+                'exception': exc,
+                'handle': handle,
+            })
 
     def _run_forever_setup(self) -> None:
         self._check_closed()

cadence/signal.py

@@ -89,7 +89,8 @@ def params_from_payload(self, data_converter: Any, payload: Any) -> list[Any]:
         type_hints = [p.type_hint for p in self._params]
         if not type_hints:
             return []
-        return data_converter.from_data(payload, type_hints)
+        result: list[Any] = data_converter.from_data(payload, type_hints)
+        return result
 
     @staticmethod
     def wrap(

tests/cadence/_internal/workflow/test_signal_handling.py

@@ -2,7 +2,6 @@
 
 from datetime import timedelta
 
-import pytest
 
 from cadence.api.v1.common_pb2 import ActivityType, Payload
 from cadence.api.v1.history_pb2 import (
@@ -340,7 +339,7 @@ def test_signal_with_empty_payload(self):
         completion = result.decisions[0].complete_workflow_execution_decision_attributes
         assert DATA_CONVERTER.from_data(completion.result, [str]) == ["notified"]
 
-    def test_async_signal_handler_raises(self):
+    def test_async_signal_handler_raises(self, caplog):
         engine = make_workflow_engine(AsyncSignalWorkflow)
         events = [
             HistoryEvent(
@@ -362,8 +361,9 @@ def test_async_signal_handler_raises(self):
             ),
         ]
 
-        with pytest.raises(NotImplementedError, match="Async signal handlers"):
+        with caplog.at_level("ERROR"):
             engine.process_decision(events)
+        assert "Async signal handlers" in caplog.text
 
     def test_multi_param_signal(self):
         """Signal handler with multiple typed parameters decodes correctly."""
@@ -422,8 +422,8 @@ def test_unknown_signal_dropped(self):
         completion = result.decisions[0].complete_workflow_execution_decision_attributes
         assert DATA_CONVERTER.from_data(completion.result, [str]) == ["notified"]
 
-    def test_signal_handler_exception_fails_decision(self):
-        """Exception in a signal handler propagates and fails the decision task."""
+    def test_signal_handler_exception_fails_decision(self, caplog):
+        """Exception in a signal handler is caught and logged by the event loop."""
         engine = make_workflow_engine(FailingSignalWorkflow)
         events = [
             HistoryEvent(
@@ -445,8 +445,9 @@ def test_signal_handler_exception_fails_decision(self):
             ),
         ]
 
-        with pytest.raises(ValueError, match="handler failed on: boom"):
+        with caplog.at_level("ERROR"):
             engine.process_decision(events)
+        assert "handler failed on: boom" in caplog.text
 
 
 class TestSameBatchOrdering: