Write a PID file in Rails

task.rb

# Sample module you can include in a rake task that checks a pid file before running
# Usage:
#  require 'task'
#
#  class Job
#    include Task
#  end
module Task
  def self.included(base)
    base.extend(ClassMethods)
  end
  
  def ClassMethods
    def run
      exit! if running?
      
      `echo foo`
      
      done!
    end

    def pid_file
      return if Rails.env.test?
      Rails.root.join('tmp', 'task.pid')
    end

    def write_pid
      return if Rails.env.test?

      File.open pid_file, "w" do |f|
        f.write Process.pid
      end
    end

    def running!
      return if Rails.env.test?

      `touch #{pid_file}`
      write_pid
    end

    def done!
      return if Rails.env.test?

      `rm #{pid_file}`
    end

    def pid
      return if Rails.env.test?

      `cat #{pid_file}`
    end

    def running?
      return if Rails.env.test?

      File.exists?(pid_file)
    end
  end
end

# Sample rake task library
namespace :job do
  class Job
    include Task
  end
  
  desc 'Run a task'
  task run: [:environment] do
    Job.run
  end
end