From: Nathan Ricci <nricci1@...3.ithaca.edu>
Date: 2002-07-24T23:48:01+09:00
Subject: Re: Can I get data back from a fork?

On Wed, 24 Jul 2002 13:15:06 +0000, Jim Freeze wrote:

> Hi:
> 
> Is there a way to get data back from a fork? Here is a little code
> snippet. I think I understand what it is doing and why it is not
> working, but I don't have much experience in this area.
> 
> class Batch
>  def initialize
>    @Job = Struct.new("Job", :pid, :result, :cmd) @job_table = {}
>  end
> 
>  def launch
>    job.pid = Process.fork { redirect(job) } @job_table[pid] = job
>  ensure
>    wait
>  end
> 
>  def redirect(job)
>    .. setup stuff
>    job.result = system(job.cmd)
>  end
  
     The problem is that when you fork, you are creating a new process. So,
sure, the two objects may have the same ID, but it is the same ID in two
seperate processes. 

     So, any way, to do what you want you have to have some way to get
the processes to talk to eachother using some kind of IPC. The most
common thing to do would be to use pipes. The other option would be to
use threads instead of seperate processes. Threads are similar, except
that the variables are all shared between the two threads of execution so
there is no need for IPC.


              --Nathan Ricci