The title is a bit exaggerated, but I want MAX clients that I can possibly have and I don’t want threads unless I need them.
Do I need a thread to accept() TCP connections?

Do I need threads for TCP recv()? If each client’s recv() is NOT ran on a separate thread, how will I differentiate them if only part of a TCP message arrived (say 30 of 111 bytes)? Which client does this incomplete recv() belong to?

Lastly, what is the least amount of server-side TCP sockets needed for this? Two? One for accept() and one for recv()/send()?

int main()
{
   thread t1(listen_accept);
   thread t2(recv_100k_clients);

   while(true) {Sleep(1000);};

   return(0);
}