Winsock recv() blocking clients app - c++

Question

I'm trying to create simple C++ server-client application, which allows multiple users to connect to server. The problem is that after creating new thread for each client, recv function started to crash clients app.
Here is my code for creating new thread for each client connected:
while (ClientSocket = accept(ListenSocket, 0, 0)) {
if (ClientSocket == INVALID_SOCKET) {
printf("\ninvalid client socket", GetLastError());
continue;
}
unsigned threadID;
HANDLE myhandleB = (HANDLE) _beginthreadex(NULL, 0, &Server::receiveMessageThread, (void *) &ClientSocket, 0,
&threadID);
}
And here is a method which is trying to receive a messages from server:
void waitForMessage() {
iResult = shutdown(ConnectSocket, SD_SEND);
if (iResult == SOCKET_ERROR) {
printf("shutdown failed with error: %d\n", WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
}
do {
iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
if ( iResult > 0 )
printf("Bytes received: %d\n", iResult);
else if ( iResult == 0 )
printf("Connection closed\n");
else
printf("recv failed with error: %d\n", WSAGetLastError());
} while( iResult > 0 );
}
After calling:
iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
client app stops responding.

Answer 1

All of your client threads are receiving a pointer to the same SOCKET variable, so they are going to trample on each other. You need to pass a copy of the SOCKET to each thread instead.
You are also leaking the HANDLE that _beginthreadex() returns if successful, and leaking the accepted SOCKET if failed.
Try this instead:
// make sure this is declared as 'static' in the 'Server' class declaration...
unsigned __stdcall Server::receiveMessageThread(void *arg)
{
SOCKET ClientSocket = (SOCKET) arg;
...
closesocket(ClientSocket);
return 0;
}
...
while (true)
{
ClientSocket = accept(ListenSocket, 0, 0);
if (ClientSocket == INVALID_SOCKET)
{
printf("\ninvalid client socket", GetLastError());
continue;
}
unsigned threadID;
HANDLE myhandleB = (HANDLE) _beginthreadex(NULL, 0, &Server::receiveMessageThread, (void *) ClientSocket, 0, &threadID);
if (myhandleB)
CloseHandle(myhandleB);
else
closesocket(ClientSocket);
}