From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-06-25T13:01:04+09:00
Subject: Re: launching process and keeping track of pid

On Sat, 25 Jun 2005, Joe Van Dyk wrote:

> 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

optfilter just takes things that looks like options and uses them as options,
things that are not hashes are arugments.  it just let's you do things like

   options = {'stdout' => StringIO::new}

   BackGroundProcess::new 'cat', options, 'stderr' => StringIO::new

or

   BackGroundProcess::new options, 'cat', 'stderr' => StringIO::new

basically it just yanks out all the hashes as options with later hashes
over-riding earlier ones... not important at all ;-)

-a
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