cache.rb

require 'dalli'

module App
  
  class Settings
    class << self
      attr_accessor :cache_ttl, :fetch_timeout, :fetch_attempt_interval
    end
  end

  class Cache
    class << self

      def fetch(name, &block)
        start = Time.now
        while Time.now - start < Settings.fetch_timeout do
          value = get(name) || lock_and_block(name, &block)
          return value if value
          Kernel.sleep Settings.fetch_attempt_interval
        end
        nil
      end
      
      def reset!
        !@dalli || @dalli.reset
        true
      end

    private
      def dalli
        return @dalli if @dalli
        @dalli = Dalli::Client.new('localhost:11211', {
          :namespace => "blah",
          :failover => false,
          :compress => true,
          :value_max_bytes => 1024 * 1024 * 10 # 10MB
        })
      end

      def get(*args)
        dalli.get(*args)
      end

      def add(*args)
        dalli.add(*args)
      end

      def delete(*args)
        dalli.delete(*args)
      end

      def lock_and_block(name, &block)
        return unless add("#{name.to_s}-lock", true, Settings.fetch_timeout)
        value = yield
        add(name, value, Settings.cache_ttl)
        delete("#{name.to_s}-lock")
        value
      end

    end
  end
end

if defined?(PhusionPassenger)
  PhusionPassenger.on_event(:starting_worker_process) do |forked|
    App::Cache.reset! if forked
  end
end