How can you lock a Mutex member in a const member function, in order to implement the Monitor Pattern?
The Monitor Pattern [SchmidtStalRohnertBuschmann] mutex should simply be declared as mutable. See the example code above. The internal state of mutex types could have been made mutable, with all lock calls made via const functions, but this does a poor job of documenting the actual semantics (and in fact would be incorrect since the logical state of a locked mutex clearly differs from the logical state of an unlocked mutex). Declaring a mutex member as mutable clearly documents the intended semantics.
