forking_supervisor.rb

#!/usr/bin/env ruby
#
# forking supervisor - forks workers and replaces dead workers.
# start it in one console, send signals to it from another console.
#

require 'rubygems'
require 'daemons/daemonize'


def logit(msg)
  if $worker
    puts "#{Time.now} worker[#{$$}] #{msg}"
  else
    puts "#{Time.now} supervisor[#{$$}] #{msg}"
  end
end

def myworker
  # this is your worker, it does something useful
  loop {
    logit "ping"
    sleep 20
  }
end

def start_worker_daemon
  p = Process.fork { $worker = true; myworker }
  logit "started worker pid=#{p}"
  p
end


if __FILE__ == $0
    # starts supervisor
    Daemonize.daemonize(logfile_name="/tmp/my.log", app_name="foo") if
      ARGV[0] == '-d'   # do you want supervisor as a daemon?

    logit "started"
    pids = Array.new
    workers = 3     # how many workers would you like today?
    logit "workers = #{workers}"
    $shutdown = false

    Signal.trap("TERM") {
      $shutdown = true
      if $worker
        # can do some worker cleanup here
        logit "Caught SIGTERM. Exiting."
      else
        logit "caught SIGTERM. Signaling child processes: #{pids.inspect}"
        pids.each { |pid|
          logit "sending SIGTERM to pid=#{pid}"
          Process.kill('TERM', pid)
          Process.waitpid(pid)
          logit "pid=#{pid} died."
        }
        logit "All child processes died."
        # can do some supervisor cleanup here
      end
      exit
    }

    Signal.trap('CLD') {
      unless $shutdown
        pids.delete(Process.wait)
        pids << start_worker_daemon
      end
    }

    while pids.size < workers
      pids << start_worker_daemon
    end

    loop { sleep 0x1000000 } rescue exit

end