The RubyUDPSocket implementation swallows exceptions that're raised. For example: line 318.

In my case I was getting Errno::ECONNREFUSED: Connection refused - send(2) exceptions raised, but I couldn't see that in JRuby. I had to switch to MRI to see it.

I'm happy to provide a patch if someone can recommend the best way to raise the exception (I don't know if there's any conventions for doing this).