launcher

Example of launcher script:

#!/usr/bin/env ruby

begin
  require 'galaxy/properties'
rescue LoadError
  $:.unshift File.join(File.dirname(__FILE__), "..", "lib")
  retry
end

ROOT = File.expand_path(File.join(File.dirname(__FILE__), ".."))

=begin

launcher command

Commands:
start
stop
restart

=end

require 'timeout'

PID_FILE = File.join(ROOT, "launcher.pid")
LOG_FILE = File.join(ROOT, "launcher.log")

def is_alive pid
  begin
    Process.kill(0, pid) == 1
  rescue Errno::ESRCH
    false
  end
end

def get_pid
  pid = nil

  begin
    File.open PID_FILE do |f|
      pid = f.read.to_i
    end

    pid = nil unless is_alive pid
  rescue Errno::ENOENT
  end

  pid
end

def save_pid pid
  File.open PID_FILE, "w" do |f|
    f.puts pid
  end
end

def wait_for pid
  loop do
    break unless is_alive pid
    sleep 0.1
  end
end

def start
  pid = get_pid

  unless pid.nil?
    puts "Already running as #{pid}"
    return -1
  end

  pid = fork do
    STDOUT.reopen LOG_FILE, "a"
    STDERR.reopen STDOUT

    child = fork do
      Dir.chdir ROOT
      exec "bin/run"
    end
    Process.detach child

    trap "TERM" do
      begin
        Process.kill Signal.list["TERM"], child

        Timeout.timeout(60 * 2) do
          wait_for child
        end
      rescue TimeoutError
        puts "Polite stop failed, sending wombats to eat process!"
        Process.kill Signal.list["KILL"], child
      end
    end

    wait_for child

    File.delete PID_FILE
  end
  Process.detach pid

  save_pid pid

  puts "Started as #{pid}"

  0
end

def stop
  pid = get_pid

  if pid.nil?
    puts "Not running"
    return 0
  end

  Process.kill Signal.list["TERM"], pid

  loop do
    break unless is_alive pid
  end

  0
end

def status
  pid = get_pid

  case pid
    when nil
      puts "Not running"
      0
    else
      puts "Running as #{pid}"
      1
  end
end

def restart
  stop
  start
end

exit case ARGV[0]
when "start"
  start
when "stop"
  stop
when "restart"
  restart
else
  status
end