- locking a mutex
  - calling cb.erase_first(n);
  - calling cb.resize(cb.capacity());
  - notify writer that there is new free space to write stuff into
  - unlocking the mutex

But the program did not work. The first thing that came to my
attention was that the checked iterators of circular_buffer don't
support this kind of multithreading as they register and unregister
themselves into a linked list without any synchronization.