From: Robert Klemme <shortcutter@...>
Date: 2008-05-21T06:35:06+09:00
Subject: Re: Arbitrary IO object

On 20.05.2008 19:34, Daniel Berger wrote:
> 
> On May 20, 11:25 am, Robert Klemme <shortcut...@googlemail.com> wrote:
>> On 20.05.2008 18:40, Daniel Berger wrote:
>>
>>> How would I go about using IO.new such that it would automatically
>>> grab the next available file descriptor?
>> Not sure what you mean: File.open uses a new file descriptor.  Why would
>> you care about the file descriptor numbering?
>>
>>> I don't know the fileno in
>>> advance and I can't use StringIO.
>> Why would you want to use StringIO to read from files?
>>
>>> What are my options?
>> What are you trying to achieve?
> 
> I'm tinkering with possibly reimplementing win32-open3 using the win32-
> process library. You can redirect stdin, stdout and stderr like so:
> 
> 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

It does not seem to make sense to open all these both for reading and 
writing.

> 
>    :app_name       => command,
>    :creation_flags => Process::DETACHED_PROCESS,
>    :startup_info   => {
>       :stdin  => input,
>       :stdout => output,
>       :stderr => error
>    }
> )

Not sure what this is supposed to do - this isn't even valid Ruby as far 
as I can see:

$ ruby -c <<EOF
 > 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
 >    }
 > )
 > EOF
-:3: syntax error, unexpected tIDENTIFIER, expecting ')'
    output = IO.new(y, 'w+') # Want next available fd
          ^
-:6: syntax error, unexpected tASSOC, expecting $end
    :app_name       => command,
                      ^

$

> pid = info.process_id
> 
> return [input, output, error, pid]
> 
> That's the general idea, anyway.

You only have two options:

- you overlay a process, then it makes sense that the new process 
inherits all standard file descriptors (0,1,2 - stdin, stdout, stderr). 
Usually nothing needs to be done for this (at least on POSIX systems)

- you copy the process (fork on POSIX) and want to be in control of the 
child' IO, in that case you need to establish pipes to feed stdin and 
read from stdout and stderr.

Kind regards

	robert