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Asynchronous Activity Completion

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Asynchronous Activity Completion enables the Activity Function to return without the Activity Execution completing.

There are three steps to follow:

1. The Activity provides the external system with identifying information needed to complete the Activity Execution. Identifying information can be a Task Token, or a combination of Namespace, Workflow ID, and Activity ID.
2. The Activity Function completes in a way that identifies it as waiting to be completed by an external system.
3. The external system uses the Temporal Client to Heartbeat and complete the Activity.

Step 1: Provide the external system with a Task Token to complete the Activity Execution. To do this, use the GetInfo() API from the go.temporal.io/sdk/activity package.

go-sandbox/activities/asynccompletion/activity.go

// Retrieve the Activity information needed to asynchronously complete the Activity.
activityInfo := activity.GetInfo(ctx)
taskToken := activityInfo.TaskToken
// Send the taskToken to the external service that will complete the Activity.
if err := a.External.Submit(ctx, taskToken, request); err != nil {
	return "", err
}

Step 2: Return an activity.ErrResultPending error to indicate that the Activity is completing asynchronously.

go-sandbox/activities/asynccompletion/activity.go

return "", activity.ErrResultPending

Step 3: Use the Temporal Client to complete the Activity using the Task Token.

go-sandbox/activities/asynccompletion/completion.go

// Instantiate a Temporal service client.
// The same client can be used to complete or fail any number of Activities.
// The client is a heavyweight object that should be created once per process.
temporalClient, err := client.Dial(client.Options{})
if err != nil {
	return err
}
defer temporalClient.Close()

// Complete the Activity.
return temporalClient.CompleteActivity(context.Background(), taskToken, result, nil)

The following are the parameters of the CompleteActivity function:

• taskToken: The value of the binary TaskToken field of the ActivityInfo struct retrieved inside the Activity.
• result: The return value to record for the Activity. The type of this value must match the type of the return value declared by the Activity function.
• err: The error to record if the Activity fails.

If err is not nil, the value of result is ignored.

While the external system works, it can call RecordActivityHeartbeat with the same Task Token so the Activity doesn't exceed its Heartbeat Timeout.

To fail the Activity, pass an error to CompleteActivity. A retryable error starts a new Activity attempt under the Activity's Retry Policy, which gives the external system a new Task Token. To fail the Activity without another attempt, use a non-retryable error:

go-sandbox/activities/asynccompletion/completion.go

// Fail the Activity. A non-retryable error stops the Retry Policy from
// starting another Activity attempt.
reason := temporal.NewNonRetryableApplicationError("order rejected", "Rejected", nil)
return temporalClient.CompleteActivity(context.Background(), taskToken, nil, reason)

To complete the Activity without a Task Token, use CompleteActivityByID. Set ActivityID in the Workflow's ActivityOptions so the external system knows which Activity ID to pass.

go-sandbox/activities/asynccompletion/completion.go

// Identify the Activity by Namespace, Workflow ID, and Activity ID.
// An empty Run ID targets the latest Run of the Workflow.
runID := ""
return temporalClient.CompleteActivityByID(context.Background(), namespace, workflowID, runID, ApprovalActivityID, result, nil)