From: Walton Hoops <me@...>
Date: 2011-02-17T12:33:22+09:00
Subject: Re: Reading/writing to spawned process

On 02/16/2011 02:14 PM, Joel F. wrote:
> Yeah it's a bit funky.  I tried on the ruby I use at work:
>
> ruby 1.9.2p136 (2010-12-25) [i386-mingw32]
>
> which turns out is the same of yours.  This one has nread and ready?
> both implemented, but both broken.  My version at home that I was using
> before was slightly older I think...so it's probably the case that
> IO/wait is a work in progress and with each version they make it
> slightly less damaged, lol.
>
> If on Windows you didn't see them, it might be that you forgot the
> 'require IO/wait'.  These methods belong to the IO method, but I think
> you need the require to "extend" the IO class (can't remember the word
> for Ruby modifying classes, but you know what I mean).
>
> It's probably just best to stick with IO.stat.size for now. It's not an
> obvious way to express things, but its worked so far.

AHHH!  It's io/wait! I tried require 'io' with no luck, and my quick 
greps didn't help me (I wasn't grepping against the C source), so I 
wasn't sure where it was supposed to be defined.  I think I can shed a 
little more light now.

On Arch Linux with Ruby-1.9.2-136:
ruby-1.9.2-p136 :002 > require 'open3'
  => true
ruby-1.9.2-p136 :003 > require 'io/wait'
  => true
ruby-1.9.2-p136 :004 > input, output, err = Open3.popen3('echo foo')
  => [#<IO:fd 4>, #<IO:fd 5>, #<IO:fd 7>, #<Thread:0x00000001d93388 run>]
ruby-1.9.2-p136 :005 > output.ready?
  => true
ruby-1.9.2-p136 :006 > err.ready?
  => false
ruby-1.9.2-p136 :007 > output.nread
  => 4
ruby-1.9.2-p136 :008 > exit

On Windows Vista with Ruby-1.9.2-136:
C:\Users\Walton Hoops>irb
irb(main):001:0> require 'io/wait'
=> true
irb(main):002:0> require 'open3'
=> true
irb(main):003:0> input, output, err = Open3.popen3('echo foo')
=> [#<IO:fd 4>, #<IO:fd 5>, #<IO:fd 7>, #<Thread:0x2a42210 run>]
irb(main):004:0> output.ready?
=> nil
irb(main):005:0> output.nread
=> 0
irb(main):006:0> output.stat.size
=> 5
irb(main):007:0> output.read
=> "foo\n"
irb(main):008:0> exit

Note: nil from ready? and 0 from nread are both meant to indicate no 
information is available (taken from the C comments)

So it quite clearly is Windows related.  After reading through wait.c 
(https://github.com/ruby/ruby/blob/trunk/ext/io/wait/wait.c) I am 
thinking that on Windows the ioctl functions (which are what io/wait 
uses) only works on socketed IO, which the results from popen3 are not 
(notice the FIONREAD_POSSIBLE_P macro is checking to see if the argument 
is a win32 socket).  I have very little expierience with the win32 APIs 
though so it might be worth confirming that with someone more knowledgeable.

I hope that helps, or at least sheds some light on things.

Walton