Ruby Daemons with DRb

daemon.rb

require 'drb'
require 'pathname'
require 'shellwords'
require 'timeout'

module DRb
  class Daemon

    PATH_KEY = 'DRB_DAEMON_PATH'
    PROTOCOL = 'drbunix:'

    def start
      if ENV.key? PATH_KEY
        STDOUT.sync = true
        STDERR.sync = true
        server = DRb.start_service(PROTOCOL, yield)
        data = {
            uri: server.uri,
            pid: $$
        }
        @path.open('w') { |f| f.write Marshal.dump data }
        server.thread.join
        @path.delete
        exit
      end
      start_daemon unless @path.exist?
      DRb.start_service(PROTOCOL)
      Signal.trap 'INT' do
        system "kill #{read_data[:pid]}"
        raise Interrupt
      end
      connect_or_start
    end

    def initialize(path)
      @path = Pathname(path)
    end

    private

    def start_daemon
      @path.parent.mkpath
      @path.delete if @path.exist?
      system "#{PATH_KEY}=#{e @path.to_s} nohup ruby #{[$0, *ARGV].shelljoin} >> #{e @path.to_s}.log 2>&1 &"
      Timeout.timeout 5 do
        loop do
          return if @path.exist?
          sleep 0.1
        end
      end
    end

    def connect_or_start
      DRb::DRbObject.new_with_uri(uri).tap { |obj| obj.respond_to? :testing123 }
    rescue DRb::DRbConnError
      start_daemon
      DRb::DRbObject.new_with_uri uri
    end

    def e(str)
      Shellwords.escape str
    end

    def uri
      @path.exist? ? read_data[:uri] : nil
    end

    def read_data
      Marshal.load @path.read
    end

  end

  def self.Daemon(path = nil, &block)
    Daemon.new(path).start &block
  end
end