Workaround for #658

[jkutner]

This is a workaround for issue #658
#658

This is the best way to handle subprocesses with IO in JRuby. I'm also working on a patch for childprocess (so that this can be removed. But this is a complete showstopper on JRuby for Vagrant right now.

[mitchellh]

Hey just did a quick review. Overall looks great. I won't be home to test on a Windows machine for a few days so I can't merge until then. However, there are some things to note that would be issues with this. Specifically, there are a lot of things that execute does that are not properly contained within execute_jruby:

• Setting the working directory (chdir)
• Timeouts
• Yielding stdin? I'm not sure how to even check this with the threaded approach, unfortunately. :(
• Yields for the outputs are going to execute on multiple threads, which would be unexpected since all code that uses subprocesses is expected to yield from the main thread, or at the very least by a single thread at a time. The simplest fix for this I believe would be to wrap the yields in a shared mutex.

I'd really love to see some sort of fix get into childprocess by @jarib since that would simplify the whole thing :( I'm not sure what the status of that is. @jarib, what do you need, exactly?

[jarib]

For some reason, you need to close the write pipes after the process has finished on JRuby. See my comment on enkessler/childprocess#30