Why is “lock (typeof (MyType))” a problem?

Question

MSDN gives the following warning about the lock keyword in C#:

In general, avoid locking on a public type, or instances beyond yo

Answer 1

It's the same problem as with lock(this) - you're locking on a reference which other code has access to, so it could be locking on it too.

If you have two unrelated pieces of code locking on the same reference without intending to exclude each other, then in the best case you could lose a bit of performance due to a lack of concurrency - and in the worst case you could introduce a deadlock.