em_mysql2_adapter.rb

# encoding: utf-8

# AR adapter for using a fibered mysql2 connection with EM
# This adapter should be used within Thin or Unicorn with the rack-fiber_pool middleware.
# Just update your database.yml's adapter to be 'em_mysql2'

module ActiveRecord
  class Base
    def self.em_mysql2_connection(config)
      client = ::Mysql2::Fibered::Client.new(config.symbolize_keys)
      options = [config[:host], config[:username], config[:password], config[:database], config[:port], config[:socket], 0]
      ConnectionAdapters::Mysql2Adapter.new(client, logger, options, config)
    end
  end
end

require 'fiber'
require 'eventmachine' unless defined? EventMachine
require 'mysql2' unless defined? Mysql2
require 'active_record/connection_adapters/mysql2_adapter'

module Mysql2
  module Fibered
    class Client < ::Mysql2::Client
      module Watcher
        def initialize(client, deferable)
          @client = client
          @deferable = deferable
        end

        def notify_readable
          begin
            detach
            results = @client.async_result
            @deferable.succeed(results)
          rescue Exception => e
            puts e.backtrace.join("\n\t")
            @deferable.fail(e)
          end
        end
      end

      def query(sql, opts={})
        super(sql, opts.merge(:async => true))
        deferable = ::EM::DefaultDeferrable.new
        ::EM.watch(self.socket, Watcher, self, deferable).notify_readable = true
        fiber = Fiber.current
        deferable.callback do |result|
          fiber.resume(result)
        end
        deferable.errback do |err|
          fiber.resume(err)
        end
        Fiber.yield
      end
    end
  end
end