Re: Loop generates never-ending sockets and threads, need help debugging

Gert-Jan de Vos <>
Fri, 5 Feb 2010 11:10:29 -0800 (PST)
On Feb 5, 6:55 pm, "Kurt" <> wrote:

Hi all,

I have a client/server project written by a hired contractor, but it's go=

t a fairly big bug when it comes to dealing with thread and sockets. It cre=
ates threads but never closes the handle to them, thus causing the server t=
o accumulate hundreds of thousands of open handles in a day or so. The clie=
nt and server both share similar code, but I'll just post the server-side.

void CTransferServer::startCommandThread() {
        int iCommandPort = _wtoi(configHandler->getTextValue(L"=


        SOCKET socCommand = CSocHandler::getServerSocket(iComma=


        if (socCommand == INVALID_SOCKET) {
                //cout << "\nCould not create transfer co=

mmand server socket." << WSAGetLastError();


        if (listen(socCommand, SOMAXCONN)) {
                //cout << "\nCould not listen on transfer=

 command port." << WSAGetLastError();

        while (blStarted) {
                SOCKET sa = accept(socCommand, 0, 0); =

                 // block for connection request

                if (sa ==INVALID_SOCKET) {
                void **params = (void **) malloc(sizeof=


                SOCKET *s = new SOCKET;
                *s = sa;
                params[0] = (void*)this;
                params[1] = (void*)s;
                DWORD dwGenericThread;
                //unsigned int iGenericThread;
                HANDLE hWorkerThread = CreateThread(NUL=

L, 0, transferCommandWorkerThread, params, 0, &dwGenericThread);

                //HANDLE hWorkerThread = (HANDLE)_begin=

threadex(NULL, 0, transferCommandWorkerThread, params, 0, &iGenericThread);

                //WaitForSingleObject(hWorkerThread, INFI=




DWORD WINAPI transferCommandWorkerThread(LPVOID param) {
        void **params = (void **)param;
        CTransferServer *transferServer = (CTransferServer*)par=


        SOCKET *commandSocket = (SOCKET*)params[1];
        delete commandSocket;
        return 0;


So, the while-loop creates a socket that accepts a connection and passes =

it off to the thread. I am not 100% familiar with sockets and threads, but =
I have a general idea about them. As far as I can tell, the workerThread do=
es close/delete the sockets properly, but the main loop never closes the ha=
ndle to the thread. I tried adding WaitForSingleObject() and CloseHandle() =
but it appears to close the thread prematurely. This causes the communicati=
on between the server and client to get disconnected or in a deadlock state=
.. I heard that _beginthreadex() is better to use, but when I tried that, I =
believe it made matters worse.

Any ideas on how to debug this or perhaps a better way of writing this?

Your analysis is correct. This is not very nice C++ code but your
problem can be fixed by using _beginthread() instead of
CreateThread(). This takes care of closing the thread handle at the
end of the thread.

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