Is working with the Session thread-safe?

Question

Consider a user making multiple requests at the same time, do I have to lock all code that works with the Session?

If for example I have the following scenario, where in

Answer 1

Yes, Session is thread-safe.

There's no need to lock anything. However, the need to check the values never cease to be essential.

Update

Check @Peter Ruderman's answer :)

I will have the decency of not copying it :)