Publicly exposing a lock, or holding the lock across method calls, is insanely poor design.
Agreed, but if one wishes to allow people to nicely enumerate collections I'm not sure there's always a good way around it. Personally, I wish that Microsoft's contract had allowed collections to be changed during an enumeration subject to some restrictions (basically, things which exist throughout an enumeration must be returned once; things that exist for part of an enumeration may be returned at most once) but that's not how Microsoft specified it. I am well aware that locking a collection during enumeration is a dangerous recipe for deadlock, but there isn't always a practical alternative.
