Jason writes:

The SetFromMap and AsLIFOQueue toString method call the toString methods
available from the collections given. For instance, the key set from the
Hashtable has a thread-safe toString method but if you wrap a Hashtable
using the SetFromMap you might get a ConcurrentModificationException when
invoking toString. The AsLIFOQueue most likely won't see the
ConcurrentModificationException (thank you weakly consistent) but might
perform fewer acquire/release of locks like in the LinkedBlockingDeque case.