winThreadPtr = (WinThread *)Tcl_Alloc(sizeof(WinThread));
    winThreadPtr->lpStartAddress = (LPTHREAD_START_ROUTINE) proc;
    winThreadPtr->lpParameter = clientData;
    winThreadPtr->fpControl = _controlfp(0, 0);

    EnterCriticalSection(&joinLock);

    *idPtr = 0; /* must initialize as Tcl_Thread is a pointer and
                 * on WIN64 sizeof void* != sizeof unsigned */

#if defined(_MSC_VER) || defined(__MSVCRT__)
    tHandle = (HANDLE) _beginthreadex(NULL, (unsigned)stackSize,
	    (Tcl_ThreadCreateProc*) TclWinThreadStart, winThreadPtr,
	    0, (unsigned *)idPtr);
#else
    tHandle = CreateThread(NULL, (DWORD)stackSize,