Using accept() and select() at the same time? - sockets

Question

I've got an event-driven network server program. This program accepts connections from other processes on other hosts. There may be many short-lived connections from different ports on the same remote IP.
Currently, I've got a while(1) loop which calls accept() and then spawns a thread to process the new connection. Each connection is closed after the message is read. On the remote end, the connection is closed after a message is sent.
I want to eliminate the overhead of setting up and tearing down connections by caching the open socket FDs. On the sender side, this is easy - I just don't close the connections, and keep them around.
On the receiver side, it's a bit harder. I know I can store the FD returned by accept() in a structure and listen for messages across all such sockets using poll() or select(), but I want to simultaneously both listen for new connections via accept() and listen on all the cached connections.
If I use two threads, one on poll() and one on accept(), then when the accept() call returns (a new connection is opened), I have to wake up the other thread waiting on the old set of connections. I know I can do this with a signal and pselect(), but this whole mess seems like way too much work for something so simple.
Is there a call or superior methodology that will let me simultaneously handle new connections being opened and data being sent on old connections?

Answer 1

Last time I checked, you could just listen on a socket and then select or poll to see if a connection came in. If so, accept it; it will not block (but you may want to really should set O_NONBLOCK just to be sure)

Answer 2

you could use listen then use select or poll then accept
if (listen(socket_fd, Number_connection) < 0 )
{
perror("listen");
return 1;
}
fd_set set;
struct timeval timeout;
int rv;
FD_ZERO(&set); /* clear the set */
FD_SET(socket_fd, &set); /* add our file descriptor to the set */
timeout.tv_sec = 20;
timeout.tv_usec = 0;
rv = select(socket_fd + 1, &set, NULL, NULL, &timeout);
if (rv == -1)
{
perror("select"); /* an error occurred */
return 1;
}
else if (rv == 0)
{
printf("timeout occurred (20 second) \n"); /* a timeout occurred */
return 1;
}
else
{
client_socket_fd = accept (socket_fd,(struct sockaddr *) &client_name, &client_name_len);
}

Answer 3

I'd put a listener in separate process(thread) not to mess things up. And run a worker process on another to handle existing sockets. There's no need for non-blocking listener really. And no thread overhead running 2 threads.
It should work like that: you accept on your listener thread till it returns you a descriptor of client socket and pass it to worker which is doing all dirty read/write job on it.
If you want to listen several ports and don't want to hold one process per listener I suggest you set your socket in O_NONBLOCK and do someth like:
// loop through listeners here and poll'em for read
// when read is successful call accept, get descriptor,
// pass it to worker and continue listen
while(1){
foreach( serverSocket in ServerSockets ){
if( serverSocket.Poll( 10, SelectRead ) ){
clientSocket = serverSocket.Accept();
// pass to worker here and release
}
}
}