Boost.Asio async_send question

Question

I\'m using Boost.Asio for a server application that I\'m writing.

async_send requires the caller to keep ownership of the data that is being sent until

Answer 1

You can't use a single vector unless you send the same and constant data to all the clients (like a prompt message). This is caused by nature of async I/O. If you are sending, the system will keep a pointer to your buffer in its queue along with some AIO packet struct. As soon as it's done with some previous queued send operations and there's a free space in its own buffer, the system will start forming packets for your data and copy chunks of your buffer inside the corresponding places in TCP frames. So if you modify content of your buffer along the way, you'll corrupt the data sent to the client. If you're receiving, the system may optimize it even further and feed your buffer to the NIC as a target for DMA operation. In this case a significant number of CPU cycles can be saved on data copying because it's done by DMA controller. Probably, though, this optimization will work only if NIC supports hardware TCP unload.

UPDATE: On Windows, Boost.Asio uses overlapped WSA IO with completion notifications via IOCP.