From: Joe Van Dyk <joevandyk@...>
Date: 2005-06-25T11:12:34+09:00
Subject: Re: launching process and keeping track of pid

On 6/24/05, Ara.T.Howard <Ara.T.Howard@noaa.gov> wrote:
> On Sat, 25 Jun 2005, Joe Van Dyk wrote:
> 
> > Hi,
> >
> > How can I launch a program from Ruby and monitor it to see if it's
> > running?  On a unix platform.
> >
> > I assume I'd probably need to launch the program, capture the pid of
> > the started process somehow, and start a thread that monitors the
> > /proc directory to see if the pid is in there?
> >
> > Thanks,
> > Joe
> 
> this might be helpful:
> 
>      #
>      # returns true if pid is running, false otherwise
>      #
>        def alive pid
> #--{{{
>          pid = Integer("#{ pid }")
>          begin
>            Process::kill 0, pid
>            true
>          rescue Errno::ESRCH
>            false
>          end
> #--}}}
>        end
>        alias alive? alive
> 

Thanks! 

I asked a question similar to this a couple months ago and you
responded with the following code.  However, my Ruby-fu isn't strong
enough to decipher it (the optfilter and IO bit).  Any chance you
could add some comments to it?


class BackGroundProcess
    attr :argv
    attr :opts
    attr :pid
    def initialize(*args)
      @argv, @opts = optfilter args
      return if((@pid = fork))
      perform_redirects
      exec(*@argv)
    end
    def perform_redirects
      if((io = (opts[:stdout] or opts['stdout'])))
        STDOUT.reopen(IO === io ? io : open(io,'w'))
      end
      if((io = (opts[:stderr] or opts['stderr'])))
        STDERR.reopen(IO === io ? io : open(io,'w'))
      end
    end
    def optfilter list
      hashes, args = list.partition{|elem| Hash === elem}
      opts = hashes.inject(accum={}){|accum, h| accum.update h}
      [ args, opts ]
    end
  end