> > Well, even with greenlets, I assume you're using at least one FD
> (socket) per client, no?
> > So you can get EMFILE on socket() just as on os.urandom(). 
> 
> I do many calls on urandom() so that's the FD bottleneck.

Unless you're doing many calls *in parallel* it's unlikely to be a
bottleneck.
At worse you can write your own /dev/urandom reading code, with a shared
fd amongst all your threads / greenlets.

os.urandom() is a convenience function, it doesn't have to be extremely
optimized.