WSAEventSelect() makes a socket descriptor no longer a socket - winsock

Question

I am writing a cross-platform socket handling library (which also handles serial and a whole bunch of other protocols in a protocol agnostic way. - I am not re-inventing the wheel).
I need to emulate the Linux poll function. The code I started with used select and worked fine, but there was no way to interrupt it from another thread, and so I was forced to start using event objects. My initial attempt called:
WSACreateEvent()
WSAEventSelect() to associate the socket with the event object.
WaitForMultipleObjectsEx() to wait on all sockets plus my interrupt event object.
select() to work out what events actually occurred on the socket.
accept()/send()/recv() to process the sockets (later and elsewhere).
This failed. accept() was claiming that the file descriptor was not a socket. If I commented out the call to WSAEventSelect(), essentially reverting to my earlier code, it all works fine (except that I cannot interrupt).
I then realised that I did something wrong (according to the Microsoft dictatorship). Instead of using select() to work out what events have happened on each socket, I should be using WSAEnumNetworkEvents(). So I rewrote my code to do it the proper way, remembering to call WSAEventSelect() afterwards to disassociate the event object from the file descriptor so that (fingers crossed) accept() would now work.
Now WSAEnumNetworkEvents() is returning an error and WSAGetLastError() tells me that the error is WSAENOTSOCK.
This IS a socket. I am doing things the way MSDN tells me I should (allowing for the general poor quality of the documentation). It appears however that WSAEventSelect() is causing the file descriptor to be marked as a file rather than a socket.
I hate Microsoft so much right now.
Here is a cut down version of my code:
bool do_poll(std::vector<struct pollfd> &poll_data, int timeout)
{
...
for (const auto &fd_data : poll_data) {
event_mask = 0;
if (0 != (fd_data.events & POLLIN)) {
// select() will mark a socket as readable when it closes (read size = 0) or (for
// a listen socket) when there is an incoming connection. This is the *nix paradigm.
// WSAEventSelect() hasseparate events.
event_mask |= FD_READ;
event_mask |= FD_ACCEPT;
event_mask |= FD_CLOSE;
}
if (0 != (fd_data.events & POLLOUT)) {
event_mask |= FD_WRITE;
}
event_obj = WSACreateEvent();
events.push_back(event_obj);
if (WSA_INVALID_EVENT != event_obj) {
(void)WSAEventSelect((SOCKET)fd_data.fd, event_obj, event_mask);
}
}
lock.lock();
if (WSA_INVALID_EVENT == interrupt_obj) {
interrupt_obj = WSACreateEvent();
}
if (WSA_INVALID_EVENT != interrupt_obj) {
events.push_back(interrupt_obj);
}
lock.unlock();
...
(void)WaitForMultipleObjectsEx(events.size(), &(events[0]), FALSE, dw_timeout, TRUE);
for (i = 0u; i < poll_data.size(); i++) {
if (WSA_INVALID_EVENT == events[i]) {
poll_data[i].revents |= POLLERR;
} else {
if (0 != WSAEnumNetworkEvents((SOCKET)(poll_data[i].fd), events[i], &revents)) {
poll_data[i].revents |= POLLERR;
} else {
if (0u != (revents.lNetworkEvents & (FD_READ | FD_ACCEPT | FD_CLOSE))) {
poll_data[i].revents |= POLLIN;
}
if (0u != (revents.lNetworkEvents & FD_WRITE)) {
poll_data[i].revents |= POLLOUT;
}
}
(void)WSAEventSelect((SOCKET)(poll_data[i].fd), NULL, 0);
(void)WSACloseEvent(event_obj);
}
}
...
}