From: Robert Klemme <shortcutter@...>
Date: 2007-09-04T19:55:30+09:00
Subject: Re: Resource Acquisition & Cleanup

2007/9/4, larsch@belunktum.dk <larsch@belunktum.dk>:
> Hello Rubyists,
>
> I am looking for a style or idiom that I can apply to a resource
> management problem. I have a number of resources (objects) that I need
> to release if any exception is thrown. While ensure-blocks or block
> parameters work well for few resources, they get cumbersome when you
> have many resources, or when the number of resources is not known.
>
> Let's say I have something similar to this:
>
> resources = []
> n.times { |i|
>    resources.push( Resource.new(i) }
> }
>
> loop {
>   # do some processing on the resources
> }
>
> n.times { |i|
>   resources[i].release
> }
>
> If an exception is thrown in the main processing loop, i still need to
> release the resources. If an exception is thrown during construction,
> i need to release the resources already succesfully created. If an
> exception is thrown while releasing a resource during exception
> handling, i still need to release the remaining resources.
>
> Is there a way to do this, especially when 'n' is unknown?

This is pretty simply and should satisfy your requirements:

def your_method(n)
  res = []
  begin
    n.times {|i| res << Resource.new(i)}

    loop do
      # main work
    end
  ensure
    res.each {|r| r.release rescue nil}
  end
end

Kind regards

robert