MutableSideEffect() panics when setting second value - cadence-workflow

Question

We're in the process of writing a .NET Cadence client and are a bit confused with how MutableSideEffect() is supposed to work. We've been thinking of the ID being passed as essentially a variable name and that developers should be able to update mutable values in a workflow. When we try this though, the second MutableSideEffect() call fails with this panic:
panic: adding duplicate decision DecisionType: Marker, ID: MutableSideEffect_value-1, state=Created, isDone()=false, history=[Created]
We munged the greetings workflow sample to make these calls:
package main
import (
"fmt"
"math/rand"
"time"
"go.uber.org/cadence/activity"
"go.uber.org/cadence/workflow"
"go.uber.org/zap"
)
/**
* This greetings sample workflow executes 3 activities in sequential. It gets greeting and name from 2 different activities,
* and then pass greeting and name as input to a 3rd activity to generate final greetings.
*/
// ApplicationName is the task list for this sample
const ApplicationName = "greetingsGroup"
// This is registration process where you register all your workflows
// and activity function handlers.
func init() {
workflow.Register(SampleGreetingsWorkflow)
activity.Register(getGreetingActivity)
activity.Register(getNameActivity)
activity.Register(sayGreetingActivity)
}
// SampleGreetingsWorkflow Workflow Decider.
func SampleGreetingsWorkflow(ctx workflow.Context) error {
// Get Greeting.
ao := workflow.ActivityOptions{
ScheduleToStartTimeout: time.Minute,
StartToCloseTimeout: time.Minute,
HeartbeatTimeout: time.Second * 20,
}
ctx = workflow.WithActivityOptions(ctx, ao)
logger := workflow.GetLogger(ctx)
var greetResult string
err := workflow.ExecuteActivity(ctx, getGreetingActivity).Get(ctx, &greetResult)
if err != nil {
logger.Error("Get greeting failed.", zap.Error(err))
return err
}
f := func(ctx workflow.Context) interface{} {
return rand.Intn(100)
}
e := func(a, b interface{}) bool {
if a == b {
return true
}
return false
}
var result int
sideEffectValue := workflow.MutableSideEffect(ctx, "value-1", f, e)
err = sideEffectValue.Get(&result)
if err != nil {
panic(err)
}
logger.Debug("MutableSideEffect-1", zap.Int("Value", result))
//************** THIS CALL FAILS **************
sideEffectValue = workflow.MutableSideEffect(ctx, "value-1", f, e)
err = sideEffectValue.Get(&result)
if err != nil {
panic(err)
}
logger.Debug("MutableSideEffect-2", zap.Int("Value", result))
// Get Name.
var nameResult string
err = workflow.ExecuteActivity(ctx, getNameActivity).Get(ctx, &nameResult)
if err != nil {
logger.Error("Get name failed.", zap.Error(err))
return err
}
// Say Greeting.
var sayResult string
err = workflow.ExecuteActivity(ctx, sayGreetingActivity, greetResult, nameResult).Get(ctx, &sayResult)
if err != nil {
logger.Error("Marshalling failed with error.", zap.Error(err))
return err
}
logger.Info("Workflow completed.", zap.String("Result", sayResult))
return nil
}
// Get Name Activity.
func getNameActivity() (string, error) {
return "Cadence", nil
}
// Get Greeting Activity.
func getGreetingActivity() (string, error) {
return "Hello", nil
}
// Say Greeting Activity.
func sayGreetingActivity(greeting string, name string) (string, error) {
result := fmt.Sprintf("Greeting: %s %s!\n", greeting, name)
return result, nil
}
Are we thinking about this correctly?

Answer 1

This is a bug in the Go client library. It happens when a MutableSideEffect with the same id is used multiple times during a single decision.
If you force a separate decision by putting workflow.Sleep(ctx, time.Second) just before the second MutableSideEffect call the problem disappears.
I filed an issue to get this fixed.
Thanks a lot for reporting!