Potential async transaction api for em-hiredis

gistfile1.rb

require 'em-hiredis'

class EM::Hiredis::Client
  class Transaction
    include EM::Deferrable
    
    def initialize(redis)
      @redis = redis
    end
    
    def prep(&block)
      @prep = block
    end
    
    def multiexec(&block)
      # Raise if called more than once
      @multiexec = block
    end
    
    def run(retries = 3)
      df = EM::DefaultDeferrable.new
      @prep.call(@redis, df)
      df.callback { |prep_results|
        @redis.multi
        @multiexec.call(@redis, *prep_results)
        df2 = @redis.exec { |results|
          if results.nil?
            if retries > 0
              EM.next_tick { run(retries - 1) }
            else
              # Transaction failed
              # TODO: Clear the watches
              self.fail()
            end
          else
            self.succeed(*results)
          end
        }
      }
      df.errback {
        # Decided not to excecute the multi-exec
        # TODO: Clear the watches
      }
    end
  end
  
  def atomically(retries = 3)
    transaction = Transaction.new(self)
    
    yield transaction
    
    transaction.run(retries)
    
    return transaction
  end
end

EM.run {
  redis = EM::Hiredis.connect
  
  df = redis.atomically do |transaction|
    transaction.prep { |r, df|
      r.watch('foo')
      EM.add_timer(3) {
        r.get('foo') { |value|
          df.succeed(value)
        }
      }
    }
    
    transaction.multiexec { |r, foo|
      p "setting bar to #{foo}"
      r.set('foo', rand)
      r.set('bar', foo)
    }
  end
  
  df.callback { |set1, set2|
    p [:transaction_result, set1, set2]
  }
}