Netflix/RxJava — pull request #1589 by g9yuayon (2014-08-15 01:44:41+00:00)
Title: Added doOnSubscribe() to Observable

We often need to be notified when an Observable is unsubscribed, for cleaning up internal states, logging, metrics gathering, and etc. With this added method, users can save the effort of writing the similar boilerplate to register a listener for un-subscription events.