Error out if waiting on socket readiness without a specified socket.

Previously we just ignored such an attempt, but that seems to serve no
purpose but making things harder to debug.

Discussion: 20160114143931.GG10941@awork2.anarazel.de
    20151230173734.hx7jj2fnwyljfqek@alap3.anarazel.de
Reviewed-By: Robert Haas

src/backend/port/unix_latch.c

@@ -226,12 +226,13 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 	int			hifd;
 #endif
 
-	/* Ignore WL_SOCKET_* events if no valid socket is given */
-	if (sock == PGINVALID_SOCKET)
-		wakeEvents &= ~(WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE);
-
 	Assert(wakeEvents != 0);	/* must have at least one wake event */
 
+	/* waiting for socket readiness without a socket indicates a bug */
+	if (sock == PGINVALID_SOCKET &&
+		(wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) != 0)
+		elog(ERROR, "cannot wait on socket event without a socket");
+
 	if ((wakeEvents & WL_LATCH_SET) && latch->owner_pid != MyProcPid)
 		elog(ERROR, "cannot wait on a latch owned by another process");
 

src/backend/port/win32_latch.c

@@ -113,12 +113,13 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 	int			result = 0;
 	int			pmdeath_eventno = 0;
 
-	/* Ignore WL_SOCKET_* events if no valid socket is given */
-	if (sock == PGINVALID_SOCKET)
-		wakeEvents &= ~(WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE);
-
 	Assert(wakeEvents != 0);	/* must have at least one wake event */
 
+	/* waiting for socket readiness without a socket indicates a bug */
+	if (sock == PGINVALID_SOCKET &&
+		(wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE)) != 0)
+		elog(ERROR, "cannot wait on socket event without a socket");
+
 	if ((wakeEvents & WL_LATCH_SET) && latch->owner_pid != MyProcPid)
 		elog(ERROR, "cannot wait on a latch owned by another process");