The inner loops in reload_all_permissions iterate role's permissions
and _anonymous_permissions maps across yield points. Concurrent
load_permissions calls (which don't hold _loading_sem) can emplace
into those same maps during a yield, potentially triggering a rehash
that invalidates the active iterator.
We want to avoid adding semaphore acquire in load_permissions
because it's on a common path (get_permissions).
Fixing by snapshotting the keys into a vector before iterating with
yields, so no long-lived map iterator is held across suspension
points.
1293b94039