nondeterministic ordering of entry points from ExtensionManager

[Brian Rosmaita]

I don't know if this is something to be fixed or maybe just the subject of a "best practice" doc for using stevedore+oslo.config generator.

The issue came up in a glance_store bug [0] where oslo.config generator appeared to be changing the ordering of some config options from run to run (it was changing the order of the driver options). Turned out that glance_store was calling ExtensionManager to get a list of entry points and using that to gather the options. If the list is sorted, the problem goes away [1].

I'm bringing it up here, because it was hard to track down. All the relevant data structures in Stevedore are ordered; I think the nondeterminism is coming from pkg_resources, maybe [2]. I don't know whether it makes sense for Stevedore to sort the list [3] or not. (I'm starting to think not, but after typing all this, I'm going to submit and let you decide.)

[0] https://bugs.launchpad.net/glance-store/+bug/1619487
[1] https://review.openstack.org/#/c/364586/3/glance_store/backend.py
[2] https://github.com/pypa/setuptools/blob/7f8144544f23f4fd84d339d846b91d4e3b703dd4/pkg_resources/__init__.py#L731
[3] https://github.com/openstack/stevedore/blob/c27ce0b878302e4894ff67bcf2df6c83812d0ba5/stevedore/extension.py#L149

[Doug Hellmann (doug-hellmann)]

Yes, the pkg_resources does not guarantee that plugins are loaded in a particular order. Sorting at the application layer is the correct solution. I suppose we could do that in stevedore, though. How big of an issue is this?

[Brian Rosmaita (brian-rosmaita)]

Not a big issue at all. We fixed it in the application layer in glance_store 0.19.0. It looks like no one else has run into it, so definitely not a big issue. I think you can close this as a "won't fix".

[Launchpad Janitor (janitor)]

[Expired for stevedore because there has been no activity for 60 days.]