I'm submitting unrelated jobs programmatically (using AWS EMR) so they run
in parallel.

I'd like to run an s3distcp job in parallel as well, but the interface to
that job is a Tool, e.g. ToolRunner.run(...).

ToolRunner blocks until the job completes though, so presumably I'd need to
create a thread pool to run these jobs in parallel.

But creating multiple threads to submit concurrent jobs via ToolRunner,
blocking on the jobs completion, just feels improper. Is there an
alternative?