SDK sockets: recv=-1 BUT WSAGetLastError=0 (???)

Hi everyone!

Something weird is happening with an application of mine:
It works OK on any computer but on one (I have nearly one hundred installations made, up and running) :confused:
The computer on which it is not running is: WinXP professional 2002 SP2 on AMD Athlon64

Mainly my app is a TCP server.
Each client has a listening thread with a loop and a call to the platform SDK Windows sockets blocking (synchronous) "recv" function (http://msdn2.microsoft.com/en-us/library/ms740121.aspx) -code below.

According to MS documentation when function "recv" returns SOCKET_ERROR (-1), an error can therefore be retrieved with WSAGetLastError.
As you can see, I check WSAGetLastError immediately after returning recv.
This works perfectly in every computer.
But on this very one computer out of 100, several times a day, "recv" returns SOCKET_ERROR (-1), BUT WSAGetLastError returns 0 :eek:
Sniffing the TCP traffic via Ethereal software I can see that, in fact, the TCP connection is still up: so it is the "recv" function that is telling me a lie.

Has this happened to anyone out there?
Have you find any Windows or Athlon64 known bug regarding this matter (recv=-1 but WSAGetLastError=0)?
Can you think of a way to make my application work on this problematic computer? :sick:

Thank you very much!

Ricardo Vázquez.
Madrid, Spain.

Code:

---

int CClientThread::Run()
{
        char msg[maxLen];

        while (!bExit) {
                int nRet = recv(clientSocket, msg, maxLen, 0);
                if (nRet == SOCKET_ERROR && bExit) {
                        // Stop closes clientSocket on exit. WSAETIMEDOUT
                        err.Format("Stop closes clientSocket on exit");
                        g_logSystem.logWarning(0, err);
                        break;
                }
                else if (nRet == SOCKET_ERROR)
                {
                        int nErr = WSAGetLastError();
                        if (nErr == 0)
                                {
                                err.Format("recv=-1 but WSAGetLastError=0 from client %s on socket %ld.", clientId, clientSocket);
                                g_logSystem.logWarning(0, err);
                                continue;
                                }
                        else
                                {
                                err.Format("Connection lost with client %s on socket %ld. Error code %ld: recv() = SOCKET_ERROR", clientId, clientSocket, nErr);
                                g_logSystem.logWarning(0, err);

                                closesocket(clientSocket);
                                server->DeleteClient(clientSocket);
                                cti_RemoveEventListener(this);
                                return SOCKET_ERROR;
                                }
                }       
                else if (!nRet) {
                        // Connection has been gracefully closed.
                        err.Format("Client %s with socket %ld has closed the connection: recv() = 0 (apparently)", clientId, clientSocket);
                        g_logSystem.logNormal(0, err);

                        closesocket(clientSocket);
                        server->DeleteClient(clientSocket);
                        cti_RemoveEventListener(this);
                        return 0;
                }
                else {
                        msg[nRet] = 0x0;
                        err.Format("[Cli %ld] Received: %s", clientSocket, msg);
                        g_logSystem.logNormal(4, err);

                        CString sMensaje;
                        sMensaje = CStrTok(msg, "%");
                        sMensaje.TrimRight();
                        sMensaje.TrimLeft();
                        while (!sMensaje.IsEmpty())
                                {
                                parse(sMensaje);
                                sMensaje = CStrTok("", "%");
                                }
                }
        }

        return 0;
}

---

Your app is multi-threaded. You might be encountering a race condition on the shared variables (like bExit).

Is the Athlon the only dual-core machine your app is running on?

Try changing the "if-then-else" logic so that the first if tests only bExit, and the second "else if" is changed to a new "if".

Mike