ipython/nbviewer — pull request #224 by minrk (2014-03-18 17:48:05+00:00)
Title: wait for pending renders of the same URL

reduces load when one URL is requested many times

A particularly egregious case was a sort of redirect loop, where a page redirected to nbviewer attempting to render the very same page.

This was able to make nbviewer inaccessible for a while, because the fetch pool would be filled up by recursive requests.