From: David Garamond <lists@...6.isreserved.com>
Date: 2004-05-31T17:31:24+09:00
Subject: elegant way to say "try this thing, one at a time, until condition is met"

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

I don't like this since I repeat unmount(). I can rewrite this as:

   def cond_met
     umount("/usr") && unmount("/usr2")
   end

   unless cond_met
     ...
     unless cond_met
       ...
         ...
     end
   end

But still it's not pretty enough. Any more elegant way?

-- 
dave