multi_worker_server.rb

#
# ServerEngine
#
# Copyright (C) 2012-2013 Sadayuki Furuhashi
#
#    Licensed under the Apache License, Version 2.0 (the "License");
#    you may not use this file except in compliance with the License.
#    You may obtain a copy of the License at
#
#        http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS,
#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#    See the License for the specific language governing permissions and
#    limitations under the License.
#
module ServerEngine

  class MultiWorkerServer < Server
    def initialize(worker_module, load_config_proc={}, &block)
      @monitors = []
      @last_start_worker_time = 0

      super(worker_module, load_config_proc, &block)
    end

    def stop(stop_graceful)
      super
      @monitors.each do |m|
        m.send_stop(stop_graceful) if m
      end
      nil
    end

    def restart(stop_graceful)
      super
      @monitors.each do |m|
        m.send_stop(stop_graceful) if m
      end
      nil
    end

    def reload
      super
      @monitors.each_with_index do |m|
        m.send_reload if m
      end
      nil
    end

    def run
      while true
        num_alive = keepalive_workers
        break if num_alive == 0
        wait_tick
      end
    end

    def scale_workers(n)
      @num_workers = n

      plus = n - @monitors.size
      if plus > 0
        @monitors.concat Array.new(plus, nil)
      end

      nil
    end

    def join_workers
      @monitors.each {|m|
        m.join if m
      }
    end

    private

    def reload_config
      super

      @start_worker_delay = @config[:start_worker_delay] || 0
      @start_worker_delay_rand = @config[:start_worker_delay_rand] || 0.2

      scale_workers(@config[:workers] || 1)

      nil
    end

    def wait_tick
      sleep 0.5
    end

    def keepalive_workers
      num_alive = 0

      @monitors.each_with_index do |m,wid|
        if m && m.alive?
          # alive
          num_alive += 1

        elsif wid < @num_workers
          # scale up or reboot
          unless @stop
            @monitors[wid] = delayed_start_worker(wid)
            num_alive += 1
          end

        elsif m
          # scale down
          @monitors[wid] = nil
        end
      end

      return num_alive
    end

    def delayed_start_worker(wid)
      if @start_worker_delay > 0
        delay = @start_worker_delay +
          Kernel.rand * @start_worker_delay * @start_worker_delay_rand -
          @start_worker_delay * @start_worker_delay_rand / 2

        now = Time.now.to_f

        wait = delay - (now - @last_start_worker_time)
        sleep wait if wait > 0

        @last_start_worker_time = now
      end

      start_worker(wid)
    end
  end

end