How to make send and recv methods work simultaneously?

Question

Send and recv methods working fine but when I send quit the recv method keeps in loop. I don't know much about multi-threading. When I send 'Q' the connection should close properly and it has to listen for clients.

How to make serve for multiple clients simultaneously?

int main()
{
    if (listen(sock, 5) == -1) {
        cerr<<"unable to listen for clients"<<endl;
        exit(1);
    }

    cout<<"TCPServer Waiting for client on port 8000"<<endl;
    sin_size = sizeof(struct sockaddr_in);

    connected = accept(sock, (struct sockaddr *)&client_addr,&sin_size);
    thread sds(snds),rvs(rcvs);
    if(sds.joinable()){
        sds.join();
    }
    if(rvs.joinable()){
        rvs.join();
    }
    close(sock);
    return 0;
}

void rcvs(){
    while(1){
        bytes_received = recv(connected,recv_data,1024,0);
        recv_data[bytes_received] = '';
        srz_rcv=recv_data;
        mb.ParseFromString(srz_rcv);
        srz_rcv=mb.msg();
        if (strcmp(srz_rcv.c_str() , "q") == 0 || strcmp(srz_rcv.c_str() , "Q") == 0){
            goto FINISH;
        }
        else{
            cout<<inet_ntoa(client_addr.sin_addr)<<" : "<<srz_rcv<<endl;
        }
        mb.Clear();
    }
    FINISH:
    close(connected);
    exit(0);
}
void snds(){
    while(1){
        cout<<"sent : ";
        cin>>send_data;
        mb.set_msg(send_data);
        mb.SerializeToString(&srz_snd);
        if (strcmp(srz_snd.c_str() , "q") == 0 || strcmp(srz_snd.c_str() , "Q") == 0){
            send(connected, srz_snd.c_str(),1024, 0);
            goto FINISH;
        }
        else{
            send(connected, srz_snd.c_str(),mb.ByteSize(), 0);
        }
        mb.Clear();
    }
    FINISH:
    close(connected);
    exit(0);
}

Post **all** of your code. For example, what is `recv_data`? — Andrew Henle, Feb 19 '16 at 12:57
server: http://pastebin.com/dMtwiiuP client: http://pastebin.com/yPm3kN25 — jsr, Feb 19 '16 at 13:22
If you want to serve N clients simultaneously, you better launch N threads. One thread for reading and one for writing don't make much sense. — n. m. could be an AI, Feb 19 '16 at 13:55
If you want to serve multiple clients at the same time, you should either use non-blocking socket IO and multiplex on it, or you should have several processing threads. Btw, get rid of `goto`, it is nasty. — SergeyA, Feb 19 '16 at 14:04
@n.m., 'One thread for reading and one for writing don't make much sense.' is not true. As a matter of fact, they make **perfect** sense. — SergeyA, Feb 19 '16 at 14:21
@SergeyA For a server? No. A server reads a request, then sends out a response. These thing never happen simultaneously. Well, almost never, but that's a long story. You certainly should not start with that. — n. m. could be an AI, Feb 19 '16 at 14:26
Does NodeJS have exactly two threads, one for reading and one for writing? If yes. I'd love to read the code. If not, this has nothing to do with the question at hand. — n. m. could be an AI, Feb 19 '16 at 16:19

score 0 · Answer 1 · edited May 23 '17 at 12:15

You seem to be closing the accepted socket when you send a "Q" or "q". If you are testing this while running both the client and server in the same process, a blocking recv might not return if you do a close( socket ). See Blocking recv doesn't exit when closing socket from another thread? The answers there suggest you can call shutdown before close. Another option is to change your recv to non-blocking and block on select instead, since that gives you more control over the conditions of the thread's wait.

On the other hand, if the "Q" or "q" is sent by a client running in a different process, your code "should" work as long as the string comparison succeeds. However, when dealing with TCP sockets, it is always advisable to shut them down gracefully. See Properly close a TCP socket Doing a shutdown and handling the subsequent read failure/fin on the remote end of the socket before doing a close is the suggested method.

Can you add more details from those sources? – Sterling Archer Feb 19 '16 at 16:24 — Sterling Archer, Feb 19 '16 at 16:24

How to make send and recv methods work simultaneously?

1 Answers1