frankfurter/lib/scheduler.rb

# frozen_string_literal: true

class Scheduler
  attr_reader :pid

  def self.start
    new.start
  end

  def initialize
    @parent_pid = Process.pid
  end

  def start
    return if pid

    @pid = fork do
      monitor_parent
      run
    end
    monitor_child
  end

  private

  def run
    load 'bin/schedule'
  end

  def monitor_child
    return if @child_monitor

    @child_monitor = Thread.new do
      loop do
        sleep 5
        unless alive?(pid)
          @pid = nil
          start
        end
      end
    end
  end

  def monitor_parent
    Thread.new do
      loop do
        exit unless alive?(@parent_pid)
        sleep 1
      end
    end
  end

  def alive?(pid)
    Process.getpgid(pid)
    true
  rescue Errno::ESRCH
    false
  end
end