Make debug mode catch mixed ET and non-ET events on an fd

Of the backends that support edge-triggered IO, most (all?) do not
support attempts to mix edge-triggered and level-triggered IO on the
same FD.  With debugging mode enabled, we now detect and refuse attempts
to add a level-triggered IO event to an fd that already has an
edge-triggered IO event, and vice versa.

1 files changed, 8 insertions, 0 deletions

diff --git a/evmap.c b/evmap.c
index b11ec3c9..cb28002a 100644
--- a/evmap.c
+++ b/evmap.c
@@ -264,6 +264,7 @@ evmap_io_add(struct event_base *base, evutil_socket_t fd, struct event *ev)
 	struct evmap_io *ctx = NULL;
 	int nread, nwrite, retval = 0;
 	short res = 0, old = 0;
+	struct event *old_ev;
 
 	EVUTIL_ASSERT(fd == ev->ev_fd);
 
@@ -300,6 +301,13 @@ evmap_io_add(struct event_base *base, evutil_socket_t fd, struct event *ev)
 		    (int)fd);
 		return -1;
 	}
+	if (EVENT_DEBUG_MODE_IS_ON() &&
+	    (old_ev = TAILQ_FIRST(&ctx->events)) &&
+	    (old_ev->ev_events&EV_ET) != (ev->ev_events&EV_ET)) {
+		event_warnx("Tried to mix edge-triggered and non-edge-triggered"
+		    " events on fd %d", (int)fd);
+		return -1;
+	}
 
 	if (res) {
 		void *extra = ((char*)ctx) + sizeof(struct evmap_io);