Are crypto(9) sessions thread safe?

[Alan Somers]

Are the sessions returned by crypto_newsession safe to use concurrently
from multiple threads?  I ask because geli currently creates a separate
thread pool for each provider, and I'm trying to change that to use a
single global thread pool.  So I need to know if different threads can
share a crypto session, or if each geli provider will still need a pool of
sessions.

-Alan