twistedcaldav.directory.idirectory interfaces should return Deferreds.

[dreid@…]

This will be essential for a pure LDAP backend using Ldaptor. Indeed it'll be necessary for any directory service using the network and the blocking appleopendirectory implementation should already be deferred to a thread to prevent blocking.

[wsanchez@…]

Well, for long-latency directory services, we probably was a persistent cache that always returns a value right away, and a background thread which refreshes the cache if the server is actively using the directory.

The flaw in the current OpenDirectory implementation is that when the cache expires, we block again. We should instead do a background cache refresh and return what's current in the cache.

However, for services where caching may not be used (eg. XMLFile), a non-blocking API is probably appropriate.