clockwork multi-thred background job
http://xoyip.hatenablog.com/entry/2014/02/17/222721
http://qiita.com/ogomr/items/27e9fc7af5b978b5ced6
http://d.hatena.ne.jp/riocampos+tech/20130625/p1
http://www.ownway.info/Ruby/index.php?clockwork%2Fabout
https://adam.heroku.com/past/2010/6/30/replace_cron_with_clockwork/
log daemon
http://d.hatena.ne.jp/riocampos+tech/20130625/p1
http://qiita.com/ogomr/items/27e9fc7af5b978b5ced6
Free Background Jobs with Google App Engine/Heroku
http://code.lancepollard.com/how-to-run-background-jobs-on-heroku-for-free
Ruby Sinatra web apps with background work threads
http://blog.markwatson.com/2011/11/ruby-sinatra-web-apps-with-background.html