Github user vrozov commented on the issue:
https://github.com/apache/drill/pull/1238
The step is necessary to do RCA for DRILL-5908. There are way too many
issues with the current implementation to list them in JIRA or PR and the major
issue is the usage of homegrown solutions where Java (or other 3rd party
libraries) already provides a required functionality out of the box. There is
no need to use `Runnable` instead of `Callable` and provide custom `Callable`
functionality. It is not necessary to wait on a `CountDownLatch` when
`ExecutionService` provides the ability to invoke all tasks and return results
when all tasks complete or a timeout expires.
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