From: Charles Oliver Nutter <headius@...>
Date: 2011-03-06T08:04:03+09:00
Subject: Re: [ANN] posix-spawn 0.3.0 -- first public release (codename, "tigers blood")

On Sat, Mar 5, 2011 at 4:16 AM, Ryan Tomayko <rtomayko@gmail.com> wrote:
> On Sat, Mar 5, 2011 at 12:07 AM, Ryan Tomayko <rtomayko@gmail.com> wrote:
>> Yes. I experimented with using spoon for JRuby support in Grit some
>> time ago. Unfortunately, a large number of posix_spawn() features
>> require real OS file descriptors and there was no standard/supported
>> way of retrieving them for most standard Java stream types.
>
> Turns out I had some of that work laying around:
>
> https://github.com/rtomayko/spoon/compare/spawn_file_actions
>
> I was able to make posix_spawn_file_actions_adddup2() and
> posix_spawn_file_actions_addclose() calls but running the test fails
> with:
>
>    $ ruby lib/spoon.rb
>    _posix_spawn_file_actions_init => 0
>    /bin/echo: write: Bad file descriptor
>    read:
...
> If you can describe a method for retrieving real fds under JRuby
> (especially IO objects returned from open() and IO.pipe()), I don't
> see any reason why we couldn't have an FFI based implementation with
> only a little more work.

As you discovered, in JRuby IO.fileno is simulated. This is mostly
because the JVM does not provide us a way to work with file
descriptors directly; everything is wrapped in a Channel or an
Input/OutputStream, and determining the real fd (if one exists) is
tricky.

However, this is a feature many people have asked for, since many
native calls need a real file descriptor. I'll look into it and see if
there's a way we can provide real file descriptor values somehow.

- Charlie