The solution to GotW #6a is now available:
GotW #6a Solution: Const-Correctness, Part 1 (updated for C ++11/14)
by Herb Sutter
From the article:
Starting with C++11,
conston a variable that is possibly shared means read-only, safe to read concurrently without external synchronization.
If you perform any operation on a
x, or call a const member function on
x, you can assume that operation does not change the observable value of
x-- or even modify the bits of
xin an observable way even in the presence of concurrency. ...
Guideline: Remember the “M&M rule”: For a member variable,
atomic) go together. ...