"David Abrahams" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > "Philippe A. Bouchard" <[EMAIL PROTECTED]> writes: > > I believe there is not that much left to do besides optimizations. > > Have you tried a comparison against a shared_ptr using an optimized > count allocator? Nobody has invested as much effort in optimizing > shared_ptr as you are pouring into shifted_ptr, but an experiment I > did years ago made a huge difference in the efficiency of shared_ptr > just by implementing a crude allocator for count objects (took me > about 10 minutes to code up). For me to find shifted_ptr convincing > I'd have to see a noticeable performance improvement over using an > optimized count allocator with shared_ptr.
My understanding is that shifted_ptr mandates allocating *your* objects inside *its* "doped memory" area by using placement new. (Phillippe, please correct me if I'm wrong.) This slashes many good uses of smart pointers, which include, but are not limited to (damn, I feel I talk like a lawyer :o)): object factories (unless they use shfted_ptr from the get-go), the Template Method pattern (ditto), cross-DLL communication, object brokers (COM/CORBA), working nicely with other allocators. All these idioms require you to grab a pointer to an object that was constructed elsewhere. If my understanding is correct, shifted_ptr is not able to do that, while shared_ptr is. These are use cases that I personally find important, so, although there existed some precedent back in 1999, I did not consider using a custom allocator (that would allocate the object plus extra memory for bookkeeping) in mc++d. At any rate, anyone comparing shifted_ptr with shared_ptr should keep in mind that one has an apple flavor and the other an orange flavor. It would be interesting to see how much the implementation of shifted_ptr is simplified if it's put into an Ownership policy of the Borg, er, loki::smart_ptr. I guess a lot. That would nicely let the users decide whether they can do with allocating objects with placement new and enjoy the additional performance. Of course, all that *after* fixing smart_ptr's buggy constructor :o). Andrei _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
