They never mention std::weak_ptr which makes me think they aren't aware of it.. yes this looks pretty useless and unsafe(isn't everything multi-threaded these days..)
There are alternative ways to utilize a machine with multiple cores, e.g. by running one thread per CPU core, and not sharing state between those threads; in each such thread you then have single-thread "semantics".
Oh sure, a single weak_ptr instance itself is not safe for multiple concurrent access of non-const methods. But weak_ptr -> shared_ptr reacquisition is atomic and all control block operations are:
> Note that the control block used by std::weak_ptr and std::shared_ptr is thread-safe: different non-atomic std::weak_ptr objects can be accessed using mutable operations, such as operator= or reset, simultaneously by multiple threads, even when these instances are copies or otherwise share the same control block internally.
The type T may be an incomplete type.
There’s no variant of shared_ptr / weak_ptr that is non atomic in the standard library AFAIK.
There are alternative ways to utilize a machine with multiple cores, e.g. by running one thread per CPU core, and not sharing state between those threads; in each such thread you then have single-thread "semantics".