Openstack is so large it also has a plethora of examples of bad code. Especially in vendor-contributed drivers and such. I wouldn't pay attention to the code so much as the incredible infrastructure and process that manages it and improves it over time.

Seriously, I've seen "sychronization threads" that use no synchronization primitives that have a single bare exception handler trap the critical section. The handler just restarts the computation... leading to fun times.

Cinder also has an interesting problem in the explosion of ABC "mixins" used for constructing a backend driver. It went from 5 in the previous release to something like 25 presently. A patch to fix it: https://review.openstack.org/#/c/201812/

But even the process isn't perfect. I've seen patches that change a couple of log lines get dog-piled with -1 nit-picks about inconsequential wording and take months to get through.

Openstack is an interesting beast but it's not a good example if you're just learning, IMO.