Blocking two threads in Windows C++ service - c++

Question

I have a Windows service written in C++ that functions as a TCP server listening for incoming connections.
I initialized the server socket and put the accept code in a separate thread. This will accept and process the incoming connections.
However, I also need to stop this thread in case the service receives the STOP signal. So I thought of creating an event object using CreateEvent and waiting for it to be signaled. This waiting would happen in the thread that creates the accept thread. So I could use the TerminateThread function to stop the accept thread when the STOP signal is received.
However, MSDN says that
TerminateThread is a dangerous function that should only be used in the most extreme cases.
How strictly should this be followed and is my approach correct? What could be another way of doing this?

Answer 1

In Windows, you can wake up a blocking accept call from another thread simply by calling closesocket. The blocking accept call will return -1 and your code has a chance to break out of whatever loop it is in by checking some other exit condition that you have already set (e.g. global variable)
This also works with Mac (and likely BSD derivatives) with the close function, but not Linux. The more universal UNIX solution to this problem is here.
Some pseduo code for the Windows solution below.
SOCKET _listenSocket;
bool _needToExit = false;
HANDLE _hThread;
void MakeListenThreadExit()
{
_needToExit = true;
closesocket(_listenSocket);
_listenSocket = INVALID_SOCKET;
// wait for the thread to exit
WaitForSingleObject(_hThread, INFINITE);
}
DWORD __stdcall ListenThread(void* context)
{
while (_needToExit == false)
{
SOCKET client = accept(_listenSocket, (sockaddr*)&addr, &addrSize);
if ((client == -1) || _needToExit)
{
break;
}
ProcessClient(client);
}
return 0;
}

Answer 2

In this situation, don't use accept() on a blocking socket. Use a non-blocking socket instead. Then you can use select() with a timeout so your thread can check for a termination condition periodically. Or better, use WSACreateEvent() with WSASelectEvent(). Create two event objects, one to detect client connections, and one to detect thread termination. You can then use WSAWaitForMultipleEvents() to wait on both events at the same time. Use WSASetEvent() to signal the termination event when needed, and call accept() or WSAAccept() whenever the other event is signalled. WSAWaitForMultipleEvents() will tell you which event to act on.