From: Christopher Kohlhoff <chris@kohlhoff.com>
--- Felipe Magno de Almeida <felipe.m.almeida@gmail.com> wrote:
win_iocp_operation is a base class that takes a pointer to a function and when called(when the IO operation is completed) it executes its pointer. The pointer is normally a static function to a derived class that calls the apropriate handler. [snip] But I dont quite follow the virtual function overhead in this case. I think that asio is reinventing the wheel and with the same overhead.
The overhead is not the virtual function call itself, but all the other stuff that gets generated by the compiler as soon as you add a virtual function to a class (e.g. vtable, RTTI etc).
Should that interface take an extra argument (void *, for example) that permits the client to get back some context? The client may need to provide a this pointer or allocate a structure on the free store and get back data needed to correctly react. If you provide for context, then you might want to combine the function pointer and context information into an object that will keep the values together not only in the win_iocp_operation invocation mentioned above, but in data members and other function calls that follow. That helps the client to combine them properly and it helps asio to keep them correctly associated. (If there are no other arguments to the win_iocp_operation invocation, then the client needn't be bothered with creating such a structure, but the implementation might still want to.) -- Rob Stewart stewart@sig.com Software Engineer http://www.sig.com Susquehanna International Group, LLP using std::disclaimer;