Github user vrozov commented on the issue:
https://github.com/apache/drill/pull/1238
I did not change how tasks (`Runnable` or `Callable`) behave and did not
look into converting `Callable/Runnable` to a `ForkJoinTask`. Whether existing
tasks can be scheduled recursively or not depends on the nature of those tasks
and is not the scope of this PR. I'd suggest filing a JIRA if one does not
exist already to look into `Fork/Join` (this is what I would expect from the
developer who put "TODO").---
