Handle illegal StateMachine transition as Non-Deterministic error (#597)

internal/error.go

@@ -113,7 +113,7 @@ type (
 
 	// PanicError contains information about panicked workflow/activity.
 	PanicError struct {
-		value      string
+		value      interface{}
 		stackTrace string
 	}
 
@@ -296,12 +296,12 @@ func (e *CanceledError) Details(d ...interface{}) error {
 }
 
 func newPanicError(value interface{}, stackTrace string) *PanicError {
-	return &PanicError{value: fmt.Sprintf("%v", value), stackTrace: stackTrace}
+	return &PanicError{value: value, stackTrace: stackTrace}
 }
 
 // Error from error interface
 func (e *PanicError) Error() string {
-	return e.value
+	return fmt.Sprintf("%v", e.value)
 }
 
 // StackTrace return stack trace of the panic

internal/internal_decision_state_machine.go

@@ -111,6 +111,11 @@ type (
 		scheduledEventIDToCancellationID map[int64]string
 		scheduledEventIDToSignalID       map[int64]string
 	}
+
+	// panic when decision state machine is in illegal state
+	stateMachineIllegalStatePanic struct {
+		message string
+	}
 )
 
 const (
@@ -306,9 +311,17 @@ func (d *decisionStateMachineBase) moveState(newState decisionState, event strin
 	}
 }
 
+func (d stateMachineIllegalStatePanic) String() string {
+	return d.message
+}
+
+func panicIllegalState(message string) {
+	panic(stateMachineIllegalStatePanic{message: message})
+}
+
 func (d *decisionStateMachineBase) failStateTransition(event string) {
 	// this is when we detect illegal state transition, likely due to ill history sequence or nondeterministic decider code
-	panic(fmt.Sprintf("invalid state transition: attempt to %v, %v", event, d))
+	panicIllegalState(fmt.Sprintf("invalid state transition: attempt to %v, %v", event, d))
 }
 
 func (d *decisionStateMachineBase) handleDecisionSent() {
@@ -660,7 +673,7 @@ func (h *decisionsHelper) getDecision(id decisionID) decisionStateMachine {
 	if !ok {
 		panicMsg := fmt.Sprintf("unknown decision %v, possible causes are nondeterministic workflow definition code"+
 			" or incompatible change in the workflow definition", id)
-		panic(panicMsg)
+		panicIllegalState(panicMsg)
 	}
 	// Move the last update decision state machine to the back of the list.
 	// Otherwise decisions (like timer cancellations) can end up out of order.
@@ -671,7 +684,7 @@ func (h *decisionsHelper) getDecision(id decisionID) decisionStateMachine {
 func (h *decisionsHelper) addDecision(decision decisionStateMachine) {
 	if _, ok := h.decisions[decision.getID()]; ok {
 		panicMsg := fmt.Sprintf("adding duplicate decision %v", decision)
-		panic(panicMsg)
+		panicIllegalState(panicMsg)
 	}
 	element := h.orderedDecisions.PushBack(decision)
 	h.decisions[decision.getID()] = element
@@ -730,12 +743,12 @@ func (h *decisionsHelper) getActivityID(event *s.HistoryEvent) string {
 	case s.EventTypeActivityTaskTimedOut:
 		scheduledEventID = event.ActivityTaskTimedOutEventAttributes.GetScheduledEventId()
 	default:
-		panic(fmt.Sprintf("unexpected event type %v", event.GetEventType()))
+		panicIllegalState(fmt.Sprintf("unexpected event type %v", event.GetEventType()))
 	}
 
 	activityID, ok := h.scheduledEventIDToActivityID[scheduledEventID]
 	if !ok {
-		panic(fmt.Sprintf("unable to find activity ID for the event %v", util.HistoryEventToString(event)))
+		panicIllegalState(fmt.Sprintf("unable to find activity ID for the event %v", util.HistoryEventToString(event)))
 	}
 	return activityID
 }

internal/internal_task_handlers.go

@@ -719,6 +719,14 @@ ProcessEvents:
 		}
 	}
 
+	// Non-deterministic error could happen in 2 different places:
+	//   1) the replay decisions does not match to history events. This is usually due to non backwards compatible code
+	// change to decider logic. For example, change calling one activity to a different activity.
+	//   2) the decision state machine is trying to make illegal state transition while replay a history event (like
+	// activity task completed), but the corresponding decider code that start the event has been removed. In that case
+	// the replay of that event will panic on the decision state machine and the workflow will be marked as completed
+	// with the panic error.
+	var nonDeterministicErr error
 	if !skipReplayCheck && !w.isWorkflowCompleted {
 		// check if decisions from reply matches to the history events
 		if err := matchReplayWithHistory(replayDecisions, respondEvents); err != nil {
@@ -728,29 +736,32 @@ ProcessEvents:
 				zap.String(tagWorkflowID, task.WorkflowExecution.GetWorkflowId()),
 				zap.String(tagRunID, task.WorkflowExecution.GetRunId()),
 				zap.Error(err))
-
-			// Whether or not we store the error in workflowContext.err makes
-			// a significant difference, to the point that it affects client's observable
-			// behavior as far as handling non-deterministic workflows.
-			//
-			// If we store it in workflowContext.err, the decision task completion code
-			// will pick up the error and correctly wrap it in the response request we sent back
-			// to the server, which in this case will contain a request to fail the workflow.
-			//
-			// If we simply return the error, the decision task completion code path will not
-			// execute at all, therefore, no response is sent back to the server and we will
-			// look like a decision task time out.
-			switch w.wth.nonDeterministicWorkflowPolicy {
-			case NonDeterministicWorkflowPolicyFailWorkflow:
-				eventHandler.Complete(nil, NewCustomError("nondeterministic workflow", err.Error()))
-			case NonDeterministicWorkflowPolicyBlockWorkflow:
-				return nil, err
-			default:
-				panic(fmt.Sprintf("unknown mismatched workflow history policy."))
+			nonDeterministicErr = err
+		}
+	}
+	if nonDeterministicErr == nil && w.err != nil {
+		if panicErr, ok := w.err.(*PanicError); ok && panicErr.value != nil {
+			if _, isStateMachinePanic := panicErr.value.(stateMachineIllegalStatePanic); isStateMachinePanic {
+				nonDeterministicErr = panicErr
 			}
 		}
 	}
 
+	if nonDeterministicErr != nil {
+		switch w.wth.nonDeterministicWorkflowPolicy {
+		case NonDeterministicWorkflowPolicyFailWorkflow:
+			// complete workflow with custom error will fail the workflow
+			eventHandler.Complete(nil, NewCustomError("NonDeterministicWorkflowPolicyFailWorkflow", nonDeterministicErr.Error()))
+		case NonDeterministicWorkflowPolicyBlockWorkflow:
+			// return error here will be convert to DecisionTaskFailed for the first time, and ignored for subsequent
+			// attempts which will cause DecisionTaskTimeout and server will retry forever until issue got fixed or
+			// workflow timeout.
+			return nil, nonDeterministicErr
+		default:
+			panic(fmt.Sprintf("unknown mismatched workflow history policy."))
+		}
+	}
+
 	return w.CompleteDecisionTask(workflowTask, true), nil
 }
 

internal/internal_task_handlers_test.go

@@ -463,7 +463,7 @@ func (t *TaskHandlersTestSuite) TestWorkflowTask_NondeterministicDetection() {
 	t.True(len(response.Decisions) > 0)
 	closeDecision := response.Decisions[len(response.Decisions)-1]
 	t.Equal(*closeDecision.DecisionType, s.DecisionTypeFailWorkflowExecution)
-	t.Contains(*closeDecision.FailWorkflowExecutionDecisionAttributes.Reason, "nondeterministic")
+	t.Contains(*closeDecision.FailWorkflowExecutionDecisionAttributes.Reason, "NonDeterministicWorkflowPolicyFailWorkflow")
 
 	// now with different package name to activity type
 	testEvents[4].ActivityTaskScheduledEventAttributes.ActivityType.Name = common.StringPtr("new-package.Greeter_Activity")