[FlightRPC][Java] Flight server can hang JVM on shutdown

[asfimport]

I noticed this while working on Flight integration tests. FlightService keeps an executor, which can hang the JVM on shutdown if the executor itself is not shut down.

It's used by Handshake and DoPut.

I think this surfaced because I wrote an AuthHandler that threw an exception.

Reporter: David Li / @lidavidm
Assignee: David Li / @lidavidm

PRs and other links:

• GitHub Pull Request #5634

_{Note: This issue was originally created as ARROW-6867. Please see the migration documentation for further details.}

[asfimport]

David Li / @lidavidm:
Aha, the real reason is

1. By default, we share an executor between gRPC and Flight.
2. gRPC doesn't take ownership of the executor, so we need to manually shut it down on exit.

The safest thing would be to clean up the executor, and document Flight as owning it.

[asfimport]

Micah Kornfield / @emkornfield:
Issue resolved by pull request 5634
#5634