Fix a warn-and-fail bug in kqueue by providing kevent() room to report errors

Apparently, kevent fails gracefully if there is not enough space in its
output events array to report every _event_... but it just dies and returns
-1 if there is not enough space to report every _error_.

There are a couple of possible fixes here.  One would to handle -1
returns from kevent better by re-growing the array and retrying... but
that seems a little error prone.  Instead, I'm just going to say that
the events array must be large enough to handle all the errors.

This patch also adds a unit test designed to make sure that our
many-events-out code works even if not all the events are added at
once.

kqueue.c

@@ -228,6 +228,23 @@ kq_build_changes_list(const struct event_changelist *changelist,
 	return n_changes;
 }
 
+static int
+kq_grow_events(struct kqop *kqop, size_t new_size)
+{
+	struct kevent *newresult;
+
+	newresult = mm_realloc(kqop->events,
+	    new_size * sizeof(struct kevent));
+
+	if (newresult) {
+		kqop->events = newresult;
+		kqop->events_size = new_size;
+		return 0;
+	} else {
+		return -1;
+	}
+}
+
 static int
 kq_dispatch(struct event_base *base, struct timeval *tv)
 {
@@ -255,6 +272,25 @@ kq_dispatch(struct event_base *base, struct timeval *tv)
 	changes = kqop->changes;
 	kqop->changes = NULL;
 
+	/* Make sure that 'events' is at least as long as the list of changes:
+	 * otherwise errors in the changes can get reported as a -1 return
+	 * value from kevent() rather than as EV_ERROR events in the events
+	 * array.
+	 *
+	 * (We could instead handle -1 return values from kevent() by
+	 * retrying with a smaller changes array or a larger events array,
+	 * but this approach seems less risky for now.)
+	 */
+	if (kqop->events_size < n_changes) {
+		int new_size = kqop->events_size;
+		do {
+			new_size *= 2;
+		} while (new_size < n_changes);
+
+		kq_grow_events(kqop, new_size);
+		events = kqop->events;
+	}
+
 	EVBASE_RELEASE_LOCK(base, th_base_lock);
 
 	res = kevent(kqop->kq, changes, n_changes,
@@ -319,17 +355,9 @@ kq_dispatch(struct event_base *base, struct timeval *tv)
 	}
 
 	if (res == kqop->events_size) {
-		struct kevent *newresult;
-		int size = kqop->events_size;
 		/* We used all the events space that we have. Maybe we should
 		   make it bigger. */
-		size *= 2;
+		kq_grow_events(kqop, kqop->events_size * 2);
-		newresult = mm_realloc(kqop->events,
-		    size * sizeof(struct kevent));
-		if (newresult) {
-			kqop->events = newresult;
-			kqop->events_size = size;
-		}
 	}
 
 	return (0);

test/regress.c

@@ -2204,7 +2204,7 @@ many_event_cb(evutil_socket_t fd, short event, void *arg)
 static void
 test_many_events(void *arg)
 {
-	/* Try 70 events that should all be aready at once.  This will
+	/* Try 70 events that should all be ready at once.  This will
 	 * exercise the "resize" code on most of the backends, and will make
 	 * sure that we can get past the 64-handle limit of some windows
 	 * functions. */
@@ -2212,6 +2212,7 @@ test_many_events(void *arg)
 
 	struct basic_test_data *data = arg;
 	struct event_base *base = data->base;
+	int one_at_a_time = data->setup_data != NULL;
 	evutil_socket_t sock[MANY];
 	struct event *ev[MANY];
 	int called[MANY];
@@ -2228,14 +2229,19 @@ test_many_events(void *arg)
 		sock[i] = socket(AF_INET, SOCK_DGRAM, 0);
 		tt_assert(sock[i] >= 0);
 		called[i] = 0;
-		ev[i] = event_new(base, sock[i], EV_WRITE, many_event_cb,
+		ev[i] = event_new(base, sock[i], EV_WRITE|EV_PERSIST,
-		    &called[i]);
+		    many_event_cb, &called[i]);
 		event_add(ev[i], NULL);
+		if (one_at_a_time)
+			event_base_loop(base, EVLOOP_NONBLOCK|EVLOOP_ONCE);
 	}
 
-	event_base_loop(base, EVLOOP_NONBLOCK);
+	event_base_loop(base, EVLOOP_NONBLOCK|EVLOOP_ONCE);
 
 	for (i = 0; i < MANY; ++i) {
+		if (one_at_a_time)
+			tt_int_op(called[i], ==, MANY - i + 1);
+		else
 			tt_int_op(called[i], ==, 1);
 	}
 
@@ -2303,7 +2309,8 @@ struct testcase_t main_testcases[] = {
 	{ "dup_fd", test_dup_fd, TT_ISOLATED, &basic_setup, NULL },
 #endif
 	{ "mm_functions", test_mm_functions, TT_FORK, NULL, NULL },
-	BASIC(many_events, TT_ISOLATED),
+	{ "many_events", test_many_events, TT_ISOLATED, &basic_setup, NULL },
+	{ "many_events_slow_add", test_many_events, TT_ISOLATED, &basic_setup, (void*)1 },
 
 	{ "struct_event_size", test_struct_event_size, 0, NULL, NULL },