How to trigger activity before processing workflow request to cancel?

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1

Hi,

In my use case, I trigger an activity to publish metrics to biq query in a finally block. However, if the workflow gets canceled, that activity is never executed or can’t be because the workflow has been canceled and will get a failed CanceledFailed ActivityFailure.

I was wondering if there is a mechanism for a workflow to trigger the activity before fully processing the cancel request. For example, add some sort of listener?

Thanks,
Derek

2

You can use detached cancellation scope.

Here is sample in the Java SDK samples repo.

3

(Just thinkin out loud). For any clean up for a workflow, shouldn’t we just always run as a detached job?

  CancellationScope detached =
            Workflow.newDetachedCancellationScope(() -> greeting = activities.sayGoodBye(name));
        detached.run();

vs. catching an exception and then handling it?

  } catch (ActivityFailure af) {
        // Create a CancellationScope that is not linked to a parent scope
        // This can be used in the "cleanup" code after the Workflow Execution has been cancelled.
        CancellationScope detached =
            Workflow.newDetachedCancellationScope(() -> greeting = activities.sayGoodBye(name));
        detached.run();
        throw af;
      }

Is there any downside with this? Also if it’s not attached to the parent scope, is it still show up in the workflow history?

4

I’m not sure I understand the question. The cleanup code has to run in a detached scope as it overwise would not be able to run anything as the surrounding scope can be canceled.

The reason try-catch is used is because any operation that is invoked from the canceled scope throws a cancelation failure. So catch is needed to perform cleanup in this case.

5

I was able to get a better understanding after reading this thread Can a child workflow/activity be triggered from a Workflow CancellationScope in the exception block? - #11 by anjo @tihomir shared with me. Thanks.

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