[Question] Why does future.get return 2 different things depending on retry logic?

[pas256]

I have the following code which asynchronously calls 2 activities and gets their results:

    a_future = Future.new.set
    b_future = Future.new.set

    a_future = activity.send_async(:a_activity, arg1)
    b_future = activity.send_async(:b_activity, arg1)

    wait_for_all(a_future, b_future)
    a_url = a_future.get
    b_url = b_future.get

    activity.c_activity(arg1, a_url, b_url)

When running this as is, I get the expected return value (which in this case is a URL) in a_url and b_url.

However, when I add retry logic to the activities

  activity :a_activity, :b_activity, :c_activity do
    {
      version: "0.0.1",
      default_task_list: $activity_task_list,
      default_task_schedule_to_start_timeout: 30,
      default_task_start_to_close_timeout: 30,
      # ADD the next 3 lines for retry logic
      exponential_retry: {
        maximum_attempts: 5,
      }
    }
  end

The value from a_future.get is now

#<AWS::Flow::Utilities::AddressableFuture:0x007fe87243d908>

That seems weird to me. Now if I want the same Workflow code to understand Activities with and without retry logic, I need a wrapper method to extract the real return value if an AddressableFuture is returned.

Have I missed something?

Also, is there a better place to ask this question?

[pas256]

Posted on Stackoverflow here:

http://stackoverflow.com/questions/23098574/how-do-i-get-the-result-of-a-retry-able-activity-using-the-aws-flow-framework-fo

and the AWS forum here:

https://forums.aws.amazon.com/thread.jspa?threadID=150379

[pmohan6]

Thanks for the question @pas256. Both Github and AWS forums are good places to ask such questions. I will get back to you on this asap. Sorry about the delay!

[pmohan6]

I agree that this behavior is a little peculiar. With asynchronous invocations of activities that have exponential retry, we have to unpack a bunch of futures to get to the actual result. You can use the AWS::Flow::Utilities::drill_on_future method to drill to the result - https://github.com/aws/aws-flow-ruby/blob/master/aws-flow/lib/aws/decider/utilities.rb#L35

The drill_on_future method looks for the #is_flow_future? method in the Future/AddressableFuture. If it is present, it drills further down till it gets to the actual result.

We will definitely look into adding more documentation about this issue.

[pas256]

Great, so drill_on_future can be used to get the results of a retryable and non-retryable activity.

Thanks for getting back to me.

[pmohan6]

Feel free to reopen if you have any more questions. Thanks!