From: Payton Swick <payton@...>
Date: 2006-01-11T01:51:25+09:00
Subject: Re: Daemonize like fetchmail

Would this be correct usage of the file, then?

    def pid
       dpid = nil
       File.open(pid_file, File::RDONLY) { |file| dpid = file.gets.chomp 
if file.flock(File::LOCK_SH|File::LOCK_NB); file.flock(File::LOCK_UN) } 
if pid_exists?
       dpid.to_i
     end


     def save_pid
       File.open(pid_file, File::CREAT|File::EXCL|File::WRONLY) { |file| 
file.puts $$ if file.flock(File::LOCK_EX); file.flock(File::LOCK_UN) }
     end

-Payton

ara.t.howard@noaa.gov wrote:
> 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