start_job

# File lib/shell/process-controller.rb, line 152
    def start_job(command = nil)
      @jobs_sync.synchronize(:EX) do
        if command
          return if command.active?
          @waiting_jobs.delete command
        else
          command = @waiting_jobs.shift

          return unless command
        end
        @active_jobs.push command
        command.start

        # start all jobs that input from the job
        for job in @waiting_jobs.dup
          start_job(job) if job.input == command
        end
      end
    end