From: ara.t.howard@...
Date: 2006-07-12T01:31:56+09:00
Subject: Re: Processes and Portability

On Wed, 12 Jul 2006, Name Name wrote:

> I would like to run a process concurrently (thus if the process goes to
> sleep or runs forever, I can still run other code from my main process) and
> have all standard out of that process be put into a text file.  I would also
> like this code to be portable.  And finally, I would like to be able to kill
> this process at any time (So I will need the pid)
>
> This thus eliminates the use of fork.  Also, I have tried:
>
> a=IO.popen("program > logfile"), but on Windows this creates two
> processes, cmd.exe and program.  a.pid only gives the pid of cmd.exe.
> And the behavior on *nix seems to be just the program (although I can be
> wrong).
>
> So I require portability in that sense.
>
> Is this possible?
>
> thanks

try this - i haven't tested on windows but it can certainly be made to work:


harp:~ > cat a.rb
#!/usr/bin/env ruby

require 'rbconfig'
require 'thread'

class Spawn
   CONFIG = Config::CONFIG

   RUBY =
     if system('ruby -e 42') # ruby is in our path
       'ruby'
     else                    # guess from rbconfig
       File.join CONFIG['bindir'], CONFIG['ruby_install_name']
     end

   PROGRAM = "p $$;STDOUT.flush;STDERR.reopen(STDOUT);exec(*ARGV)"

   ATTRIBUTES = %w[
     mutex
     out
     exitstatus
     exitstatus_q
     cmd
     pipe
     pid
     thread
   ]

   ATTRIBUTES.each{|a| attr_accessor a}

   def initialize *argv
     @mutex = Mutex.new
     @out = ''
     @exitstatus = nil
     @exitstatus_q = Queue.new
     @cmd = "#{ RUBY } -e '#{ PROGRAM }' #{ argv.join(' ') }"
     @pipe = IO.popen @cmd
     @pid = @pipe.gets.to_i
     at_exit{ Process.kill -9, @pid rescue nil }
     @thread = Thread.new{
       begin
         while((line = @pipe.gets))
           @mutex.synchronize{ @out << line }
         end
       ensure
         @pipe.close rescue nil
         exitstatus = $?.exitstatus
         @exitstatus_q.push exitstatus
       end
     }
   end

   def out
     @mutex.synchronize{ @out }
   end

   def exitstatus non_block = false
     @exitstatus ||= @exitstatus_q.pop(non_block)
   end

   class << self; alias [] new; end
end


require 'yaml'

cmd = ARGV.join ' '

spawn = Spawn[ cmd ]

y 'spawn.cmd' => spawn.cmd
y 'spawn.pid' => spawn.pid
y 'spawn.exitstatus' => spawn.exitstatus
y 'spawn.out' => spawn.out



harp:~ > ruby a.rb date
spawn.cmd: ruby -e 'p $$;STDOUT.flush;STDERR.reopen(STDOUT);exec(*ARGV)' date
spawn.pid: 27232
spawn.exitstatus: 0
spawn.out: |
   Tue Jul 11 10:31:22 MDT 2006


harp:~ > ruby a.rb no-exist
spawn.cmd: ruby -e 'p $$;STDOUT.flush;STDERR.reopen(STDOUT);exec(*ARGV)' no-exist
spawn.pid: 27235
spawn.exitstatus: 1
spawn.out: |
   -e:1:in `exec': No such file or directory - no-exist (Errno::ENOENT)
         from -e:1


regards.

-a
-- 
suffering increases your inner strength.  also, the wishing for suffering
makes the suffering disappear.
- h.h. the 14th dali lama