server.rb

    def execute(cmd)
      response = nil

      begin
        input = prepare_operation(cmd)
        Log.info "received command: #{input[:command]}, args: #{input[:args]}"
        semaphore.synchronize { repository.send(input[:command], *input[:args]) }
      rescue ClientError => e
        Log.error "input error: #{e.message}"
        response = 'ERROR'
        raise e
      rescue RepositoryError => e
        Log.error "repository opeartion error: #{e.message}"
        response = 'FAIL'
      else
        Log.info "command OK"
        response = 'OK'
      end

      response
    end