demo script for demonizing using fork exec

minor refinements to demon

script/demon_test/child

@@ -0,0 +1,31 @@
+#!/usr/bin/env ruby
+
+$parent_pid = ARGV[0].to_i
+
+puts "Hello from #{Process.pid} my parent is #{$parent_pid}"
+
+Thread.new do
+
+  def alive?(pid)
+    Process.kill(0, pid)
+    true
+  rescue
+    false
+  end
+
+  while true
+    begin
+      unless alive?($parent_pid)
+        STDERR.puts "Parent was terminated!"
+        Process.kill "TERM", Process.pid
+        sleep 10
+        Process.kill "KILL", Process.pid
+      end
+    rescue => e
+      STDERR.puts "URGENT monitoring thread had an exception #{e}"
+    end
+    sleep 1
+  end
+end
+
+sleep

script/demon_test/parent.rb

@@ -0,0 +1,25 @@
+require File.expand_path("../../../config/environment", __FILE__)
+
+puts "Parent is now loaded"
+
+class ForkExecDemon < Demon::Base
+  def self.prefix
+    "fork-exec-child"
+  end
+
+  def run
+    if @pid = fork
+      write_pid_file
+      return
+    end
+
+    exec "./child #{parent_pid}"
+  end
+end
+
+ForkExecDemon.start(1, verbose: true)
+
+while true
+  ForkExecDemon.ensure_running
+  sleep 0.1
+end