From: nobu.nokada@...
Date: 2004-05-31T18:19:12+09:00
Subject: Re: elegant way to say "try this thing, one at a time, until condition is met"

Hi,

At Mon, 31 May 2004 17:31:24 +0900,
David Garamond wrote in [ruby-talk:101855]:
> 
> Example: I need to unmount /usr and /usr2, but currently I can't because 
> there are some opened files from those partitions. I am going to try 
> shutting down daemons or killing some processes (or other things), one 
> at a time, until I can unmount it.
> 
>   def kill(process, signal)
>     ...
>   end
> 
>   # returns false if failed, true if succeeded or already unmounted
>   def unmount(partition)
>    ...
>   end
> 
>   unless unmount("/usr") && unmount("/usr2")
>     system "/etc/init.d/httpd stop"
>     system "/etc/init.d/squid stop"
>     unless unmount("/usr") && unmount("/usr2")
>       kill("rdiff-backup", :TERM)
>       sleep 3
>       unless unmount("/usr") && unmount("/usr2")
>         kill("rdiff-backup", :KILL)
>         sleep 3
>         ...
>           ...
>       end
>     end
>   end

What about:

  count = 0
  until unmount("/usr") && unmount("/usr2")
    case count += 1
    when 1
      system "/etc/init.d/httpd stop"
      system "/etc/init.d/squid stop"
    when 2
      kill("rdiff-backup", :TERM)
      sleep 3
    when 3
      kill("rdiff-backup", :KILL)
      sleep 3
    end
  end

or:

  stopper = [
    proc {
      system "/etc/init.d/httpd stop"
      system "/etc/init.d/squid stop"
    },
    proc {
      kill("rdiff-backup", :TERM)
      sleep 3
    },
    proc {
      kill("rdiff-backup", :KILL)
      sleep 3
    }
  ]
  until unmount("/usr") && unmount("/usr2")
    stopper.shift.call
  end

-- 
Nobu Nakada