boost::asio::ip::udp::socket can I force an immediate send or write?

Question

I'm working on up programme using boost::asio::ip::udp:: socket where I need at certain moment send a buffer to a specific end point with high priority (I need a guarantee that my data was delivered to the end point and I should see it in tcmpdump capture) My question is about the function boost::asio::ip::udp::socket::send, is it possible that the system cache the data and don't deliver immediately. With this kind of function. I have to fflush the socket if i need to send a high priority data ? Which is the best approach i have to follow it for this use case ?

Thanks :)