Executor threads not being created as daemon #817
Description
There appears to be an executor service somewhere in concurrent-ruby that's not marking the threads as "daemon" on JVM. As a result, this causes that executor to keep the process from terminating.
This issue has been affecting builds of JRuby for some time; the CRuby standard library test suite we run appears to trigger concurrent-ruby to create this executor, resulting in the entire suite hanging at the end when it should gracefully shut down.
I am not sure where the code is for launching such an executor...someone else might be able to find this quickly. I will try.
