Reduce Admin API calls by caching returned values. The cache is not
enabled by default, because it could result in stale values being
returned. It can be enabled by setting 'cache_enabled' to True on
Qubes() object. This is safe in two cases:
- the application don't care about changed values - like a short-lived
process that retrieve values once (for example qvm-ls)
- the application listen for events and invalidate cache when property
is changed
For the second case, invalidating the cache on appropriate event
(property-set:*, property-reset:*) is done before calling other event
handlers. This is because the event may try to access the property value
(not necessary from the event arguments), so we need to be sure it will
see the new value.
FixesQubesOS/qubes-issues#5415
218d43a2e0