It's not in 1.33.1, is it? It may not bring performance benefits, still, it is a usefull feature to have.
No, it isn't in 1.33.1. It will be in 1.34, though. _______________________________________________
But 1.33.1 uses it internally? Since after defining this macro I was able to measure some performance benefits.
It is used internally, yes. You can check how its done in detail/sp_counted_impl.hpp and detail/quick_allocator.hpp. However, underneath the quick allocator still relies on the global new operator (for allocating pages) and uses whatever heap the global new/delete operators use. That's okay for a single heap environments. It's just that it cannot be used when multiple heaps enter the picture. In published versions it is possible to specify a deletor for the contained object, but not the custom allocator/deletor for the shared count. Therefore, a shared count may end up in a different heap than the contained object and that could lead to the visibility problems. As a matter of fact, I will be interesting to see how this was done. We tried to modify the code into this direction but run into some problems, and since there was a pressure to deliver (as there always is) we then used a backup plan and guarded the (infrequently used) shared heap by other means. Best regards, Leon Mlakar