C++ multithread socket cannot receive client data - c++

Question

I would like to create a multithreaded socket server. I have the server working fine, but when i try to move my code into a worker function the server stops working when reading the client data.
original code:
main.cpp
int sock;
main(){
SocketServer *ss = new SocketServer(8888);
pthread_t thread;
if(ss != NULL){
while(true){
sock = ss->Accept();
char* out;
ss->GetRequest(sock, out);
}
}
}
SocketServer.cpp
void SocketServer::GetRequest(int msgsock, char* out){
char buf[1024];
int rval;
std::cout<<"before read\n";
if ((rval = read(msgsock, buf, 1024)) < 0){
perror("reading socket");
}else{
strcpy(out,buf);
}
std::cout<<"after read\n";
}
After adding threads:
main.cpp
int sock;
main(){
SocketServer *ss = new SocketServer(8888);
pthread_t thread;
if(ss != NULL){
while(true){
sock = ss->Accept();
pthread_create(&thread, NULL, SocketThread, &(*ss));
pthread_detach(thread);
}
}
}
static void* SocketThread(void* lp){
SocketServer *ss = (SocketServer*) lp;
char* out;
ss->GetRequest(sock, out);
}
Original outputs:
before read
after read
New outputs:
before read

Answer 1

This is broken:
if ((rval = read(msgsock, buf, 1024)) < 0){
perror("reading socket");
}else{
strcpy(out,buf);
You are ignoring rval unless it signals an error. It should be:
if ((rval = read(msgsock, buf, 1024)) < 0){
perror("reading socket");
else if (rval == 0) {
// peer closed the connection
close(msgsock); // or closesocket(), depending on your platform
break;
}else{
strncpy(out,buf,rval);
and this is also broken:
sock = ss->Accept();
pthread_create(&thread, NULL, SocketThread, &(*ss));
The thread started to handle the client has no interest in the listening socket. What it needs is the accepted socket sock, and it needs to get it in such a way that it won't be overridden on the next call. Typically sock is a local variable in the accept loop and is passed via pthread_create().