[jira] [Created] (REEF-687) Restructure handler for DriverRestart in Java

["Andrew Chung (JIRA)" <ji...@apache.org>]

Andrew Chung created REEF-687:
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             Summary: Restructure handler for DriverRestart in Java
                 Key: REEF-687
                 URL: https://issues.apache.org/jira/browse/REEF-687
             Project: REEF
          Issue Type: Sub-task
            Reporter: Andrew Chung
            Assignee: Andrew Chung


Currently, ``DriverRestartHandler`` only informs about the ``StartTime``, which is not very helpful. The way the rest of the restart mechanism is set up, users can also be confused in the following ways:
1. When ``EvaluatorFailedHandler`` is called, the user does not know for sure whether it is called on a failed Evaluator from a previous Driver instance or from the current Driver instance without keeping a list of ``AllocatedEvaluators.``
2. When ``DriverRestartCompletedHandler`` is called, the user cannot easily find out whether it is called due to a timeout expiration or due to the fact that all Evaluators have already either failed or reported back.

The proposal is to return 2 sets of Evaluator IDs, those that have failed on restart, and those that are expected to report back in the ``DriverRestartHandler``, along with ``StartTime``. Although it's still not as explicit for both 1 and 2, this lets users know what to expect.

There will also be items to make 1 and 2 more explicit.
For 1, an item will be filed to create a special ``DriverRestartEvaluatorFailedHandler``. For 2, an item will be filed to extend the ``DriverRestartCompletedHandler`` to pass back an object that includes the set of failed Evaluator IDs.



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