From: Gary Wright <gwtmp01@...>
Date: 2008-05-21T03:36:54+09:00
Subject: Re: Arbitrary IO object


On May 20, 2008, at 1:34 PM, Daniel Berger wrote:
>
> info = Process.create(
>    input  = IO.new(x, 'w+')  # Want next available fd
>    output = IO.new(y, 'w+') # Want next available fd
>    error  = IO.new(z, 'w+')  # Want next available fd
>
>    :app_name       => command,
>    :creation_flags => Process::DETACHED_PROCESS,
>    :startup_info   => {
>       :stdin  => input,
>       :stdout => output,
>       :stderr => error
>    }
> )

IO.new is for associating a Ruby IO object with
an already open OS file descriptor.   So you've got
to acquire the file descriptor through some non-Ruby
mechanism in order to be useful via IO.new.  You can
use IO#fileno to discover the underlying OS file
descriptor from a Ruby object but if you've already
got a Ruby IO object you don't need to use IO.new.

At the C/POSIX level I don't think there is really
any concept of specifying the 'next available fd'.
You just call open/create/pipe/dup and use the integer
file descriptors that are returned.  The OS figures
out which integer descriptors are available.

Gary Wright