From: ara.t.howard@...
Date: 2007-02-23T00:38:46+09:00
Subject: Re: Restore Kernel.binding to a previous state

On Fri, 23 Feb 2007, Hans Sjunnesson wrote:

> Hey all,
>
> I'm implementing a simple queue system with which I'm evaling 'jobs',
> like so:
>
> code = lambda {eval(job)}
> code.call
>
> Where 'job' is a string containing ruby code.
> The problem I'm having is that I need these jobs to evaluate in a
> clean environment, uncluttered by the previous jobs. What I'd like is
> something along the lines of this:
>
> temp = Kernel.binding
> code = lambda {eval(job)}
> code.call
> Kernel.binding = temp
>
> Though that looks sort of dangerous.
> Another idea might be to be able to create a binding which is a deep
> copy of the current binding. I'm not sure if this has been done before.
>

   http://www.linuxjournal.com/article/7922
   http://codeforpeople.com/lib/ruby/rq/

if you're on windows you're out of luck though.  in any case, all you need is
a closure defined early on in your program.  from there you evaluate the code.
for example

harp:~ > cat a.rb
require 'thread'

jq = SizedQueue.new 1
rq = SizedQueue.new 1

runner = Thread.new do
   loop do
     job = jq.pop

     rq.push Thread.new{
       $SAFE = 4
       begin
         eval job
       rescue Exception => e
         e
       end
     }.value
   end
end

x = 42

jq.push 'x = 42.0; x'
p rq.pop

jq.push 'x = :forty_two; x'
p rq.pop


harp:~ > ruby a.rb
42.0
:forty_two


basically you set of a thread server which, itself, is a thread.  the top
level thread is a closure of the initial context, so each new thread only has
access to that clean environment.  this does not reset the environment, but it
does run each job in a clean one without poluting the current one.

regards.

-a
-- 
be kind whenever possible... it is always possible.
- the dalai lama