Hi Thorsten, --- Thorsten Ottosen <nesotto@cs.aau.dk> wrote:
please consider the other mails too. there are too many drawback in void* IMO.
I have seen/used code where a statically allocated data was far slower than putting it on the heap. This wsa not stack-allocated, but static data. So I'm a bit concerned about performance claims.
The performance problems of requiring vector<char> or char[N] exist on several levels: - For vector<char>, there is the initialisation of the chars to 0 on construction or when you do a resize. Note that this is proportional to the size of the vector, not necessarily to the amount of data transferred. I have seen this have a noticable cost in a CPU-bound server handling thousands of connections. - Requiring a copy from a native data structure into vector<char> or char[N]. If I have an array of a doubles say, I should be able to send it as-is to a peer that has identical architecture and compiler. Avoiding unnecessary data copying is a vital part of implementing high performance protocols. I also believe that the argument that the cost is not significant compared to network I/O does not hold when you are developing an application using asynchronous I/O, since the time spent sending/receiving no longer blocks the application.
If the only performance sensible iterator types are T*, I would't mind simply
template< unsigned N > void receive( char (&)[N] );
template< unsigned N > void receive( char (&)[N], unsigned size );
void recieve( vector<char>& );
void recieve( vector<char>&, unsigned size );
or something.
I just realised that you cannot have such functions on the socket class due to the possibility of a short send or receive. Since you can send or receive fewer bytes than requested, how would you implement something like asio::send_n or asio::recv_n on top of the above functions? Again, I believe that adding safety is best done in layers, in accordance with the don't pay for what you don't need principle: asio::socket::send/recv etc taking void* + size_t. These functions can result in a short send or receive. ^ | asio::send_n/recv_n etc taking void* + size_t. These functions attempt to transfer the all of the requested data. ^ | asio::send_?/recv_? etc. New functions that take safe types like vector<char> and char[N]. Cheers, Chris