what happand to socket, when the other end close it? - c++

Question

I want to develop a client server app and I want to make it as robust as possible. There are multiple questions come up for me, and I just can't find an unambiguous answer on the internet.
Let's say, that the server is running on a while(TRUE) loop and check for command existance is it's commands queue, if there is one, it sends it, if there isn't one, it just continue to the head of the loop.
But what if the other end went down, or there is a connection error between the two, what happen to the socket value, does it become INVALID_SOCKET?
while (TRUE) {
if (ReqQueue->size() != 0 && ReqQueue->front() != string("STOP")) { // there is some command in the ReqQueue which is NOT STOP.
int sent = send(ClientSocket, ReqQueue->front().c_str(), (int)strlen(ReqQueue->front().c_str()), 0);
if (sent == (int)strlen(ReqQueue->front().c_str()))
ReqQueue->pop(); // Next Command.
else if (int err = WSAGetLastError() == WSAETIMEDOUT){
shutdown(ClientSocket, SD_BOTH);
closesocket(ClientSocket);
return;
}
else
continue;
}
else if (ReqQueue->size() == 0) {
continue;
}
else if(ReqQueue->front() == string("STOP"))
{
if (send(ClientSocket, "STOP", strlen("STOP"), 0) == strlen("STOP")) {
/*Message received indication from target*/
shutdown(ClientSocket, SD_BOTH);
closesocket(ClientSocket);
return;
}
}
}
shutdown(ClientSocket, SD_BOTH);
closesocket(ClientSocket);
return 0;
that's the source :)
what I want to ask is, there is a better way to implement the above goal, maybe I can change the while loop condition to something like while(the socket is OK) or while(there is still a connection).

Answer 1

what happen to the socket value
Nothing. A send() on that socket will eventually fail, and a recv() on it will deliver zero or -1, but the socket itself remains open, and the variable value is unaffected. There is no magic.
does it become INVALID_SOCKET?
No.

Answer 2

For me, better idea would be when you receive a request to your server from any client, just create a new thread and assign the task to that thread. By doing that you can make your server parallel processing of client request and work on multiple request from multiple client. Hence no client need to wait for server to complete the request of a client already submitted a request. If you implement like this you don’t need to bother what will happened if a connection broken. In normal case if a correction broken you will get this information in your server while sending the reply to the client and you can mark that process as failed and log it into server log.