Hi Felipe, --- 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. There's a comment above win_iocp_operation that is this:
// Base class for all IOCP operations. A function pointer is used instead of // virtual functions to avoid the associated overhead.
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). Since you can very easily end up with many win_iocp_operation-derived classes in your application (one for each callback handler) using virtual functions can contribute to significant code bloat on some compilers (e.g. MSVC6, although with MSVC7.1 it appears to optimise unused RTTI away). By doing this little workaround, I can guarantee for all compilers that the overhead for each handler is limited to a single function, which is called through a function pointer. Cheers, Chris