Cancellation

This pages shows the following:

• How to handle a Cancellation request within a Workflow.
• How to set an Activity Heartbeat Timeout.
• How to listen for and handle a Cancellation request within an Activity.
• How to send a Cancellation request from a Temporal Client.

Handle Cancellation in Workflow

How to handle a Cancellation in a Workflow in Go.

Workflow Definitions can be written to handle execution cancellation requests with Go's defer and the workflow.NewDisconnectedContext API. In the Workflow Definition, there is a special Activity that handles clean up should the execution be cancelled.

If the Workflow receives a Cancellation Request, but all Activities gracefully handle the Cancellation, and/or no Activities are skipped then the Workflow status will be Complete. It is completely up to the needs of the business process and your use case which determines whether you want to return the Cancellation error to show a Canceled status or Complete status regardless of whether a Cancellation has propagated to and/or skipped Activities.

sample-apps/go/features/cancellation/workflow.go

// ...
// YourWorkflow is a Workflow Definition that shows how it can be canceled.
func YourWorkflow(ctx workflow.Context) error {
// ...
	activityOptions := workflow.ActivityOptions{
// ...
		HeartbeatTimeout:    5 * time.Second,
		// Set WaitForCancellation to true to have the Workflow wait to return
		// until all in progress Activities have completed, failed, or accepted the Cancellation.
		WaitForCancellation: true,
	}
	defer func() {
		// This logic ensures cleanup only happens if there is a Cancelation error
		if !errors.Is(ctx.Err(), workflow.ErrCanceled) {
			return
		}
		// For the Workflow to execute an Activity after it receives a Cancellation Request
		// It has to get a new disconnected context
		newCtx, _ := workflow.NewDisconnectedContext(ctx)
		// This Activity is only executed if
		err := workflow.ExecuteActivity(newCtx, a.CleanupActivity).Get(ctx, nil)
		if err != nil {
			logger.Error("CleanupActivity failed", "Error", err)
		}
	}()
// ...
	err := workflow.ExecuteActivity(ctx, a.ActivityToBeCanceled).Get(ctx, &result)
// ...
	// This call to execute the Activity is expected to return an error "canceled".
	// And the Activity Execution is skipped.
	err = workflow.ExecuteActivity(ctx, a.ActivityToBeSkipped).Get(ctx, nil)
// ...
	// Return any errors.
	// If a CanceledError is returned, the Workflow changes to a Canceled state.
	return err
}

Handle Cancellation in an Activity

How to handle a Cancellation in an Activity in Go.

Ensure that the Activity is Heartbeating to receive the Cancellation request and stop execution.

View the source code

in the context of the rest of the application code.

// ActivityToBeCanceled is the Activity that will respond to the Cancellation Request
func (a *Activities) ActivityToBeCanceled(ctx context.Context) (string, error) {
// ...
	// A for select statement is a common approach to listening for a Cancellation is an Activity
	for {
		select {
		case <-time.After(1 * time.Second):
			logger.Info("Heartbeating...")
			activity.RecordHeartbeat(ctx, "")
		// Listen for ctx.Done() to know if a Cancellation Request has propagated to the Activity.
		case <-ctx.Done():
			logger.Info("This Activity is canceled!")
			return "I am canceled by Done", nil
		}
	}
}
// ...

Request Cancellation

How to request Cancellation of a Workflow and Activities in Go.

Use the CancelWorkflow API to cancel a Workflow Execution using its Id.

View the source code

in the context of the rest of the application code.

func main() {
// ...
	// Call the CancelWorkflow API to cancel a Workflow
	// In this call we are relying on the Workflow Id only.
	// But a Run Id can also be supplied to ensure the correct Workflow is Canceled.
	err = temporalClient.CancelWorkflow(context.Background(), cancellation.WorkflowId, "")
	if err != nil {
		log.Fatalln("Unable to cancel Workflow Execution", err)
	}
// ...
}