From: Dan Zwell <dzwell@...>
Date: 2007-09-04T19:16:49+09:00
Subject: Re: Resource Acquisition & Cleanup

larsch@belunktum.dk wrote:
> 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?
> 
> Regards,
> Lars
> 
> 
> 

How about this? It should catch and print exceptions that happen during 
release, but continue looping through the rest of the array.

resources.each do |resource|
   begin
     resource.release
   rescue => err
     puts err
   end
end

If you want to also do this upon exceptions in the main processing loop, 
I would make it into a method and call it like this:

def release(resources)
   resources.each do |resource|
     begin
       resource.release
     rescue => err
       p err
     end
   end
end

n.times { |i|
    resources.push( Resource.new(i) }
}

begin
   loop {
     # do some processing on the resources
   }
rescue => err
   p err
   # release resources upon error:
   release(resources)
ensure
   # release resources if there is no error:
   release(resources)
end

Hope this helps,
Dan