Child workflow cancellation in presence of coroutine results in "lookup failed for scheduledEventID to activityID"


I’ve met an unexpected trouble when I tried to cancel child workflow on the event received from background coroutine, hope you’ll explain if it’s my fault or not.

In actual workflow I have background coroutine performing some polling activity and sending results through channel and child workflow which should be canceled on some event, and when that event happens main workflow panics with “lookup failed for scheduledEventID to activityID”.

Minimal code to reproduce:

package main

import (

	tlog ""

const TaskQueue = "cancel"

const heartbeatInterval = 1 * time.Second

func Parent(ctx workflow.Context) error {
	options := workflow.ActivityOptions{
		StartToCloseTimeout: 2 * time.Minute,
	ctx = workflow.WithActivityOptions(ctx, options)
	ch := workflow.NewChannel(ctx)
	logger := workflow.GetLogger(ctx)
	child, cancel := spawnChild(ctx)
	if err := child.GetChildWorkflowExecution().Get(ctx, nil); err != nil {
		return fmt.Errorf("failed to start child workflow: %w", err)
	workflow.GoNamed(ctx, "ctl", func(ctx workflow.Context) {
		ctl(ctx, ch, logger)
	res := ""
	for {
		s := workflow.NewSelector(ctx)
			func(c workflow.ReceiveChannel, more bool) {
				_ = c.Receive(ctx, &res)

		logger.Info("Received", "Value", res)
		if res == "cancel" {
			r := child.Get(ctx, nil)
			logger.Info("Canceled", "Result", r)
	if err := workflow.Sleep(ctx, 30*time.Second); err != nil {
		logger.Error("Workflow sleep failed", "Error", err)
	return nil

func Child(ctx workflow.Context) error {
	options := workflow.ActivityOptions{
		StartToCloseTimeout: 2 * time.Minute,
	ctx = workflow.WithActivityOptions(ctx, options)
	if err := wait(ctx); err != nil {
		return fmt.Errorf("wait failed: %w", err)
	return nil

func Wait(ctx context.Context, d time.Duration) error {
	deadline := time.Now().Add(d)
	attempt := 0
	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-time.After(heartbeatInterval):
			activity.RecordHeartbeat(ctx, attempt)
		if time.Now().After(deadline) {
			return nil

func spawnChild(ctx workflow.Context) (workflow.ChildWorkflowFuture, func()) {
	ctx, cancel := workflow.WithCancel(ctx)
	ctx = workflow.WithChildOptions(ctx, workflow.ChildWorkflowOptions{
		WaitForCancellation: true,
	return workflow.ExecuteChildWorkflow(ctx, Child), cancel

func wait(ctx workflow.Context) error {
	t := 100 * 365 * 24 * time.Hour
	ctx = workflow.WithActivityOptions(ctx, workflow.ActivityOptions{
		StartToCloseTimeout: t,
		WaitForCancellation: true,
		HeartbeatTimeout:    30 * time.Second,
	return workflow.ExecuteActivity(ctx, Wait, t).Get(ctx, nil)

func ctl(ctx workflow.Context, ch workflow.Channel, logger tlog.Logger) {
	for {
		if err := workflow.ExecuteActivity(
			ctx, Wait, 1*time.Second,
		).Get(ctx, nil); err != nil {
			logger.Error("Wait failed", "Error", err)
		} else {
			ch.Send(ctx, "cancel")

func main() {
	c, err := client.NewClient(client.Options{})
	if err != nil {
		log.Fatalln("unable to create Temporal client", err)
	defer c.Close()
	w := worker.New(c, TaskQueue, worker.Options{})
	err = w.Run(worker.InterruptCh())
	if err != nil {
		log.Fatalln("unable to start Worker", err)

And its error:

2021/10/13 13:18:38 ERROR Workflow panic Namespace default TaskQueue cancel WorkerID 2132641@localhost@ WorkflowType Parent WorkflowID b6d5ed4a-3620-4898-a6c2-6e1c03e0308c RunID 061d626c-5782-49df-ba43-cf071a2469a2 Attempt 2 Error lookup failed for scheduledEventID to activityID: scheduleEventID: 17, activityID: 16 StackTrace process event for cancel [panic]:
	.../go/pkg/mod/*commandsHelper).handleActivityTaskScheduled(0xc0004ec230, 0xc000122530, 0x2, 0x11)
	.../go/pkg/mod/ +0x165*workflowExecutionEventHandlerImpl).ProcessEvent(0xc0003981f8, 0xc000496ec0, 0x1, 0x0, 0x0)
	.../go/pkg/mod/ +0x45b*workflowExecutionContextImpl).ProcessWorkflowTask(0xc0003c61c0, 0xc0003c9830, 0x1471b20, 0xc00031a690, 0xc0003c61c0, 0x0)
	.../go/pkg/mod/ +0x72c*workflowTaskHandlerImpl).ProcessWorkflowTask(0xc00049c000, 0xc0003c9830, 0xc0004de390, 0x0, 0x0, 0x0, 0x0)
	.../go/pkg/mod/ +0x6d9*workflowTaskPoller).processWorkflowTask(0xc000492270, 0xc0003c9830, 0x0, 0x0)
	.../go/pkg/mod/ +0x4ae*workflowTaskPoller).ProcessTask(0xc000492270, 0xd02760, 0xc0003c9830, 0x0, 0x0)
	.../go/pkg/mod/ +0x85*baseWorker).processTask(0xc0004a8000, 0xd02320, 0xc0004801b0)
	.../go/pkg/mod/ +0xb8
created by*baseWorker).runTaskDispatcher
	.../go/pkg/mod/ +0xff

Event history for parent:

1  WorkflowExecutionStarted                        Oct 13th 1:18:37 pm Close Timeout identity tctl@localhost Workflow Parent
2  WorkflowTaskScheduled                                               Taskqueue cancel Timeout 10s
3  WorkflowTaskStarted                                                 requestId bde662e3-9878-46bd-a016-d28f0be33bf6
4  WorkflowTaskCompleted                                               identity 2132641@localhost@
5  StartChildWorkflowExecutionInitiated                                Taskqueue cancel Workflow Child
6  ChildWorkflowExecutionStarted                                       Workflow Child - 061d626c-5782-49df-ba43-cf071a2469a2_5
7  WorkflowTaskScheduled                                               Taskqueue localhost:9fff2b4a-e875-4d99-bfa1-4203d6271561 Timeout 10s
8  WorkflowTaskStarted                                                 requestId 6b4e5800-10e3-4ab6-9821-507bd829d3fa
9  WorkflowTaskCompleted                                               identity 2132641@localhost@
10 ActivityTaskScheduled                                               Close Timeout Id 10 input [ 1000000000 ] Name Wait
11 ActivityTaskStarted                                                 attempt 1 identity 2132641@localhost@ requestId e0c7c083-7421-42f3-a0d2-d94744dde9fc
12 ActivityTaskCompleted                           1s (+1s) 
13 WorkflowTaskScheduled                           1s                  Taskqueue localhost:9fff2b4a-e875-4d99-bfa1-4203d6271561 Timeout 10s
14 WorkflowTaskStarted                             1s                  requestId 890e099a-518e-44e4-aecd-679a90d14f1a
15 WorkflowTaskCompleted                           1s                  identity 2132641@localhost@
16 RequestCancelExternalWorkflowExecutionInitiated 1s                  workflowTaskCompletedEventId 15 namespace default workflowExecution.workflowId 061d626c-5782-49df-ba43-cf071a2469a2_5 workflowExecution.runId control childWorkflowOnly true
17 ActivityTaskScheduled                           1s                  Close Timeout Id 16 input [ 1000000000 ] Name Wait
18 ExternalWorkflowExecutionCancelRequested        1s                  initiatedEventId 16 namespace default workflowExecution.workflowId 061d626c-5782-49df-ba43-cf071a2469a2_5 workflowExecution.runId
19 WorkflowTaskScheduled                           1s                  Taskqueue localhost:9fff2b4a-e875-4d99-bfa1-4203d6271561 Timeout 10s
20 WorkflowTaskStarted                             1s                  requestId 49846d98-240f-4883-bde1-03c33265182f
21 WorkflowTaskFailed                              1s                  message lookup failed for scheduledEventID to activityID: scheduleEventID: 17, activityID: 16

One may notice that cancellation process parts are interleaved with activity schedule and possibly this leads to incorrect behaviour. Also when I protect event processing section (loop body) with sort of semaphore using variable and workflow.Await() in ctl() function error disappears but I had an impression that it shouldn’t be necessary because Temporal uses cooperative multitasking and goroutines and channels don’t require such protection.

Software versions:
Go 1.16
Temporal server 1.12.3
Temporal SDK 1.10.0 and 1.9.0

1 Like

I can confirm this reproduces and is a bug. We’re taking a look at a fix :slight_smile: – thank you for the extremely high quality report

This is a good catch! The order of operations on child workflow cancelation was reported differently than when it actually happened. I have opened a fix for this at Fix command ordering issue on child workflow cancel by cretz · Pull Request #588 · temporalio/sdk-go · GitHub granted it may change during review.