socket connection lost using select function - sockets

Question

I'm newbee in socket program.
I made my server program with good sample program using select function.
It works well about 20,000 connections over.
But, in some case, connection accept twice consequence without
receive data from first socket.
Only data received from second socket connection.
After that, first socket resource cannot release.
FD_SET and FD_ISSET are not working with first socket in case of consequence accept I think.
Working clients are 6.
Before this situation,
accept, receive data, and close socket, accept, rcv
data, close, ...
In case, accept,
accept, receive data from second socket, and close second socket.
Lost first socket connection.
After that, accept function assign second socket descriptor.
What is problem?
How can release fisrt socket?
BR
Paul

Answer 1

My code is as follow:
while(1)
{
//clear the socket set
FD_ZERO (&readfds);
//add master socket to set
FD_SET (sever_socket, &readfds);
max_sd = sever_socket;
//add child sockets to set
for ( i = 0 ; i < MAX_CLIENT ; i ++)
{
//socket descriptor
sd = client_socket [i];
//if valid socket descriptor then add to read list
if (sd > 0)
{
FD_SET( sd , &readfds);
}
//highest file descriptor number, need it for the select function
if(sd > max_sd)
{
max_sd = sd;
}
}
//wait for an activity on one of the sockets , timeout is NULL , so wait indefinitely
activity = select ( max_sd + 1 , &readfds , NULL , NULL , NULL);
if ((activity < 0) && (errno!=EINTR))
{
LOG_F (WARNING, "select error");
}
//If something happened on the master socket, then its an incoming connection
if (FD_ISSET(sever_socket, &readfds))
{
if ((new_socket = accept (sever_socket, (struct sockaddr *) &address, (socklen_t*) &addrlen)) < 0)
{
perror("accept");
exit(EXIT_FAILURE);
}
//inform user of socket number - used in send and receive commands
LOG_F (INFO, "New connection, socket fd is %d, ip is : %s, port : %d",
new_socket, inet_ntoa(address.sin_addr), ntohs(address.sin_port));
//add new socket to array of sockets
for (i = 0; i < MAX_CLIENT; i++)
{
//if position is empty
if( client_socket[i] == 0 )
{
client_socket[i] = new_socket;
LOG_F (INFO, "Adding to list of sockets as %d" , i);
break;
}
}
}
for (i = 0; i < MAX_CLIENT; i++)
{
sd = client_socket[i];
if (FD_ISSET (sd , &readfds))
{
memset (&rcvBuf, 0x00, sizeof(rcvBuf));
if ((fp = fdopen (sd, "r")) == NULL)
{
LOG_F (WARNING, "TCP_SOCKET FD_OPEN Error");
close (sd);
client_socket[i] = 0;
}
else
{
ret = ioctl (sd, FIONREAD, &nread);
if (nread == 0)
{
fclose (fp);
close (sd);
client_socket[i] = 0;
LOG_F (WARNING, "Client disconnected(as %d, fd %d)", i, sd);
}
else
{
len = recv (sd, rcvBuf, nread, 0);
if (len > 0)
{
LOG_F (INFO, "RECV size %d" , len);
...
do_msg_handler ()
}
}
...