Back-patch fixes for some issues in our Windows socket code into 9.1.

This is a backport of commit b85427f2276d02756b558c0024949305ea65aca5.
Per discussion of bug #4958.  Some of these fixes probably need to be
back-patched further, but I'm just doing this much for now.

src/backend/port/win32/socket.c

@@ -137,6 +137,7 @@ pgwin32_waitforsinglesocket(SOCKET s, int what, int timeout)
 	HANDLE		events[2];
 	int			r;
 
+	/* Create an event object just once and use it on all future calls */
 	if (waitevent == INVALID_HANDLE_VALUE)
 	{
 		waitevent = CreateEvent(NULL, TRUE, FALSE, NULL);
@@ -150,20 +151,19 @@ pgwin32_waitforsinglesocket(SOCKET s, int what, int timeout)
 				(errmsg_internal("could not reset socket waiting event: %i", (int) GetLastError())));
 
 	/*
-	 * make sure we don't multiplex this kernel event object with a different
+	 * Track whether socket is UDP or not.  (NB: most likely, this is both
-	 * socket from a previous call
+	 * useless and wrong; there is no reason to think that the behavior of
+	 * WSAEventSelect is different for TCP and UDP.)
 	 */
-
 	if (current_socket != s)
-	{
-		if (current_socket != -1)
-			WSAEventSelect(current_socket, waitevent, 0);
 		isUDP = isDataGram(s);
-	}
-
 	current_socket = s;
 
-	if (WSAEventSelect(s, waitevent, what) == SOCKET_ERROR)
+	/*
+	 * Attach event to socket.  NOTE: we must detach it again before returning,
+	 * since other bits of code may try to attach other events to the socket.
+	 */
+	if (WSAEventSelect(s, waitevent, what) != 0)
 	{
 		TranslateSocketError();
 		return 0;
@@ -196,10 +196,14 @@ pgwin32_waitforsinglesocket(SOCKET s, int what, int timeout)
 
 				r = WSASend(s, &buf, 1, &sent, 0, NULL, NULL);
 				if (r == 0)		/* Completed - means things are fine! */
+				{
+					WSAEventSelect(s, NULL, 0);
 					return 1;
+				}
 				else if (WSAGetLastError() != WSAEWOULDBLOCK)
 				{
 					TranslateSocketError();
+					WSAEventSelect(s, NULL, 0);
 					return 0;
 				}
 			}
@@ -210,6 +214,8 @@ pgwin32_waitforsinglesocket(SOCKET s, int what, int timeout)
 	else
 		r = WaitForMultipleObjectsEx(2, events, FALSE, timeout, TRUE);
 
+	WSAEventSelect(s, NULL, 0);
+
 	if (r == WAIT_OBJECT_0 || r == WAIT_IO_COMPLETION)
 	{
 		pgwin32_dispatch_queued_signals();
@@ -219,7 +225,10 @@ pgwin32_waitforsinglesocket(SOCKET s, int what, int timeout)
 	if (r == WAIT_OBJECT_0 + 1)
 		return 1;
 	if (r == WAIT_TIMEOUT)
+	{
+		errno = EWOULDBLOCK;
 		return 0;
+	}
 	ereport(ERROR,
 			(errmsg_internal("unrecognized return value from WaitForMultipleObjects: %i (%i)", r, (int) GetLastError())));
 	return 0;
@@ -543,9 +552,12 @@ pgwin32_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, c
 		if (writefds && FD_ISSET(sockets[i], writefds))
 			flags |= FD_WRITE | FD_CLOSE;
 
-		if (WSAEventSelect(sockets[i], events[i], flags) == SOCKET_ERROR)
+		if (WSAEventSelect(sockets[i], events[i], flags) != 0)
 		{
 			TranslateSocketError();
+			/* release already-assigned event objects */
+			while (--i >= 0)
+				WSAEventSelect(sockets[i], NULL, 0);
 			for (i = 0; i < numevents; i++)
 				WSACloseEvent(events[i]);
 			return -1;
@@ -565,9 +577,9 @@ pgwin32_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, c
 		for (i = 0; i < numevents; i++)
 		{
 			ZeroMemory(&resEvents, sizeof(resEvents));
-			if (WSAEnumNetworkEvents(sockets[i], events[i], &resEvents) == SOCKET_ERROR)
+			if (WSAEnumNetworkEvents(sockets[i], events[i], &resEvents) != 0)
 				ereport(FATAL,
-						(errmsg_internal("failed to enumerate network events: %i", (int) GetLastError())));
+						(errmsg_internal("failed to enumerate network events: %i", (int) WSAGetLastError())));
 			/* Read activity? */
 			if (readfds && FD_ISSET(sockets[i], readfds))
 			{
@@ -594,10 +606,10 @@ pgwin32_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, c
 		}
 	}
 
-	/* Clean up all handles */
+	/* Clean up all the event objects */
 	for (i = 0; i < numevents; i++)
 	{
-		WSAEventSelect(sockets[i], events[i], 0);
+		WSAEventSelect(sockets[i], NULL, 0);
 		WSACloseEvent(events[i]);
 	}
 

src/backend/port/win32_latch.c

@@ -108,10 +108,11 @@ WaitLatchOrSocket(volatile Latch *latch, pgsocket sock, bool forRead,
 	numevents = 2;
 	if (sock != PGINVALID_SOCKET && (forRead || forWrite))
 	{
+		/* Need an event object to represent events on the socket */
 		int			flags = 0;
 
 		if (forRead)
-			flags |= FD_READ;
+			flags |= (FD_READ | FD_CLOSE);
 		if (forWrite)
 			flags |= FD_WRITE;
 
@@ -154,11 +155,10 @@ WaitLatchOrSocket(volatile Latch *latch, pgsocket sock, bool forRead,
 			Assert(sock != PGINVALID_SOCKET);
 
 			ZeroMemory(&resEvents, sizeof(resEvents));
-			if (WSAEnumNetworkEvents(sock, sockevent, &resEvents) == SOCKET_ERROR)
+			if (WSAEnumNetworkEvents(sock, sockevent, &resEvents) != 0)
 				ereport(FATAL,
-						(errmsg_internal("failed to enumerate network events: %i", (int) GetLastError())));
+						(errmsg_internal("failed to enumerate network events: %i", (int) WSAGetLastError())));
-
+			if ((forRead && resEvents.lNetworkEvents & (FD_READ | FD_CLOSE)) ||
-			if ((forRead && resEvents.lNetworkEvents & FD_READ) ||
 				(forWrite && resEvents.lNetworkEvents & FD_WRITE))
 				result = 2;
 			break;
@@ -167,10 +167,10 @@ WaitLatchOrSocket(volatile Latch *latch, pgsocket sock, bool forRead,
 			elog(ERROR, "unexpected return code from WaitForMultipleObjects(): %d", (int) rc);
 	}
 
-	/* Clean up the handle we created for the socket */
+	/* Clean up the event object we created for the socket */
-	if (sock != PGINVALID_SOCKET && (forRead || forWrite))
+	if (sockevent != WSA_INVALID_EVENT)
 	{
-		WSAEventSelect(sock, sockevent, 0);
+		WSAEventSelect(sock, NULL, 0);
 		WSACloseEvent(sockevent);
 	}