5分钟后线程停止工作

Question

我使用＆＃34; Running Rails jobs in background threads＆＃34;中描述的技术实现了异步文件处理：

def upload_images
    begin
      uploaded_io = params[:filetoupload]
      File.open(Rails.root.join('public', 'uploads', uploaded_io.original_filename), 'wb') do |file|
        file.write(uploaded_io.read)
        file.flush
        job = Job.create(:status => 0, :file_name => uploaded_io.original_filename)
        processing_job(job)
      end
    rescue => e
      upload_log.error(e.to_s)
    end
    redirect_to '/admin/jobs'
  end

  def processing_job(job)
    background do
      # do processing
    end
  end

  def background(&block)
    Thread.new do
      yield
      ActiveRecord::Base.connection.close
    end
  end

但是在大​​约5分钟的工作后，线程停止处理数据：记录停止，CPU负载几乎为零。免费记忆也不是问题。

为什么会发生这种情况以及如何解决？

我使用Ruby 1.9.3p551，Rails 4.1.9，Phusion Passenger 4.0.59。