I have seen complains from e.g. Tarek that os.urandom() fails under high load: https://twitter.com/tarek_ziade/status/362281268215418880

The problem is caused by file descriptor limits. os.urandom() opens /dev/urandom for every call. How about os.urandom() uses a persistent file descriptor? That should eliminate the error. It may alsos speed up os.urandom() because a persistent FD gets rid of open() and close() syscalls.

* open /dev/urandom on first call of os.urandom() and store the fd in a static var
* invalidate, close fd on read() -> EINVAL; open /dev/urandom again
* close fd when interpreter shuts down