horizon's nova api should cache extensions list

[Rob Raymond]

Currently nova api code memoize's calls to get extensions from nova. But there is a cache hit only if request arg is the same.
Since get extensions is called in many places and extensions are not dynamic, we should cache more aggressively regardless of request.

[Yves-Gwenael Bourhis (yves-gwenael-bourhis)]

I started working on it.

I started by making a new memoization decorator to which I pass the attributes of "request" I want to use for memoization.
the list_extensions method only needs the 'user' attribut of the request.
I noticed the following: The user instance of the request object is always the same... even when logging out and in again...
weakref.ref references the same object when logging out and logging in another user because only the user object's attributes (tenant_id, etc...) are changed.... This means that memoizing on the user will not work unless we instantiate a new user object instead of changing the attribute values.

I'll push a draft soon.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/150392

[OpenStack Infra (hudson-openstack)]

Change abandoned by David Lyle (<email address hidden>) on branch: master
Review: https://review.openstack.org/150392
Reason: This review is > 4 weeks without comment, and failed Jenkins the last time it was checked. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and leaving a 'recheck' comment to get fresh test results.

[Yves-Gwenael Bourhis (yves-gwenael-bourhis)]

review reactivated, sorry for the delay.