How does epoll work internally?

How does IFTTT work internally?

• For instance, how does IFTTT know about a post that is made on Craigslist? Does it register a listener on Craigslist somehow?

• Answer:

  In the case of Craigslist all you need is an RSS parser since Craigslist produces RSS feeds for all it's postings. For example if you wanted the RSS feed for all the accounting/finance jobs in London the URL would be like this: http://london.craigslist.co.uk/search/acc?format=rss Now I don't know exactly what IFTTTs setup is since I don't work for them, however I would guess that they have a server polling and analyzing RSS feeds on craigslist every few minutes. Once you have found the data that you're looking for all you need to do is something useful with it. The polling can be optimized by working out how often to check by looking at how often updates are made.