From: ara.t.howard@...
Date: 2006-01-11T00:23:56+09:00
Subject: Re: Daemonize like fetchmail

On Tue, 10 Jan 2006, Payton Swick wrote:

> Well, I did it myself anyway. Hope it's useful:
> http://rubyforge.org/projects/pidify/
>
> -Payton

it does look useful.  few comments/suggestions though

   - since it's *nix specify anyhow you might want to use O_EXCL when opening
     the file since otherwise there is a race condition to create the file

   - on the same page using File#flock with File::LOCK_EX when writing and
     File::LOCK_SH for writing and reading (with File::LOCK_NB of course) will
     avoid the race conditions and possibibity of reading a half-baked file

   - escalation of signals with a pause between is useful for killing processes
     since many trap signit and most do not die immediately.  something like

       def maim(pid, signals=%w(SIGTERM SIGQUIT SIGKILL), suspend=4)
         pid = Integer("#{ pid }")
         signals = [ signals ].flatten.map{|sig| "#{ sig }"}
         suspend = Integer("#{ suspend }")

         existed = false
         sigs.each do |sig|
           begin
             Process::kill(sig, pid)
             existed = true
           rescue Errno::ESRCH
             return(existed ? true : nil)
           end
           return true unless alive?(pid)
           sleep suspend
           return true unless alive?(pid)
         end
         return(not alive?(pid))
       end

     which makes sure the process is actually dead prevents removing the
     pidfile in cases where the Process::kill didn't work

   - the alive function above can be something like this

       def alive pid
         pid = Integer("#{ pid }")
         begin
           Process::kill 0, pid
           true
         rescue Errno::ESRCH
           false
         end
       end

cheers.

-a
-- 
===============================================================================
| ara [dot] t [dot] howard [at] noaa [dot] gov
| strong and healthy,
| who thinks of sickness until it strikes like lightning?
| preoccupied with the world,
| who thinks of death, until it arrives like thunder?
| -- milarepa
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