Remove the eventqueue list and the ev_next pointers.

Those pointers were once used to maintain a complete list of
inserted IO and signal events.  But such a list is now available by
walking over ev_io_map and ev_signal_map!  So all they did was
require extra pointer operations to maintain, and extra 8-16 bytes
of storage in each struct event.

To be cowardly and keep the option of going back to having this
redundancy, I'm wrapping the removed code in a set of ifdefs.

This is a first cut; it needs cleanups and stress-testing!!  In
particular, it just plain disables a couple of functions that could
probably be saved.

There seems to be a need for an evmap_{io,signal}_foreach() or something.

event-internal.h

@@ -232,8 +232,10 @@ struct event_base {
 	/** Mapping from signal numbers to enabled (added) events. */
 	struct event_signal_map sigmap;
 
+#ifdef _EVENT_USE_EVENTLIST
 	/** All events that have been enabled (added) in this event_base */
 	struct event_list eventqueue;
+#endif
 
 	/** Stored timeval; used to detect when time is running backwards. */
 	struct timeval event_tv;

event.c

@@ -590,7 +590,9 @@ event_base_new_with_config(const struct event_config *cfg)
 	gettime(base, &base->event_tv);
 
 	min_heap_ctor(&base->timeheap);
+#ifdef _EVENT_USE_EVENTLIST
 	TAILQ_INIT(&base->eventqueue);
+#endif
 	base->sig.ev_signal_pair[0] = -1;
 	base->sig.ev_signal_pair[1] = -1;
 	base->th_notify_fd[0] = -1;
@@ -764,14 +766,8 @@ event_base_free(struct event_base *base)
 	}
 
 	/* Delete all non-internal events. */
-	for (ev = TAILQ_FIRST(&base->eventqueue); ev; ) {
-		struct event *next = TAILQ_NEXT(ev, ev_next);
-		if (!(ev->ev_flags & EVLIST_INTERNAL)) {
-			event_del(ev);
-			++n_deleted;
-		}
-		ev = next;
-	}
+	evmap_signal_delete_all(base);
+	evmap_io_delete_all(base);
 	while ((ev = min_heap_top(&base->timeheap)) != NULL) {
 		event_del(ev);
 		++n_deleted;
@@ -821,7 +817,9 @@ event_base_free(struct event_base *base)
 
 	mm_free(base->activequeues);
 
+#ifdef _EVENT_USE_EVENTLIST
 	EVUTIL_ASSERT(TAILQ_EMPTY(&base->eventqueue));
+#endif
 
 	evmap_io_clear(&base->io);
 	evmap_signal_clear(&base->sigmap);
@@ -2638,7 +2636,9 @@ event_queue_remove_inserted(struct event_base *base, struct event *ev)
 	}
 	DECR_EVENT_COUNT(base, ev);
 	ev->ev_flags &= ~EVLIST_INSERTED;
+#ifdef _EVENT_USE_EVENTLIST
 	TAILQ_REMOVE(&base->eventqueue, ev, ev_next);
+#endif
 }
 static void
 event_queue_remove_active(struct event_base *base, struct event *ev)
@@ -2743,7 +2743,9 @@ event_queue_insert_inserted(struct event_base *base, struct event *ev)
 
 	ev->ev_flags |= EVLIST_INSERTED;
 
+#ifdef _EVENT_USE_EVENTLIST
 	TAILQ_INSERT_TAIL(&base->eventqueue, ev, ev_next);
+#endif
 }
 
 static void
@@ -3030,6 +3032,8 @@ evthread_make_base_notifiable(struct event_base *base)
 void
 event_base_dump_events(struct event_base *base, FILE *output)
 {
+#ifdef _EVENT_USE_EVENTLIST
+	/* re-enable XXXXXX */
 	struct event *e;
 	int i;
 	fprintf(output, "Inserted events:\n");
@@ -3056,6 +3060,7 @@ event_base_dump_events(struct event_base *base, FILE *output)
 					(e->ev_res&EV_TIMEOUT)?" Timeout active":"");
 		}
 	}
+#endif
 }
 
 void

evmap-internal.h

@@ -90,6 +90,9 @@ void *evmap_io_get_fdinfo(struct event_io_map *ctx, evutil_socket_t fd);
 int evmap_io_reinit(struct event_base *base);
 int evmap_signal_reinit(struct event_base *base);
 
+int evmap_io_delete_all(struct event_base *base);
+int evmap_signal_delete_all(struct event_base *base);
+
 void evmap_check_integrity(struct event_base *base);
 
 #endif /* _EVMAP_H_ */

evmap.c

@@ -547,6 +547,45 @@ evmap_signal_reinit(struct event_base *base)
 	return res;
 }
 
+int
+evmap_io_delete_all(struct event_base *base)
+{
+	struct event_io_map *io = &base->io;
+
+#ifdef EVMAP_USE_HT
+	struct event_map_entry **mapent;
+	HT_FOREACH(mapent, event_io_map, io) {
+		struct evmap_io *ctx = &(*mapent)->ent.evmap_io;
+#else
+	evutil_socket_t i;
+	for (i = 0; i < io->nentries; ++i) {
+		struct evmap_io *ctx = io->entries[i];
+		if (!ctx)
+			continue;
+#endif
+		while (LIST_FIRST(&ctx->events))
+			event_del(LIST_FIRST(&ctx->events));
+	}
+
+	return 0;
+}
+
+int
+evmap_signal_delete_all(struct event_base *base)
+{
+	struct event_signal_map *sigmap = &base->sigmap;
+	int i;
+
+	for (i = 0; i < sigmap->nentries; ++i) {
+		struct evmap_signal *ctx = sigmap->entries[i];
+		if (!ctx)
+			continue;
+		while (!LIST_EMPTY(&ctx->events))
+			event_del(LIST_FIRST(&ctx->events));
+	}
+	return 0;
+}
+
 /** Per-fd structure for use with changelists.  It keeps track, for each fd or
  * signal using the changelist, of where its entry in the changelist is.
  */
@@ -798,6 +837,8 @@ evmap_check_integrity(struct event_base *base)
 	int nsignals, ntimers, nio;
 	nsignals = ntimers = nio = 0;
 
+#ifdef _EVENT_USE_EVENTLIST
+	/* XXXXX no-eventlist implementations can use some of this, surely? */
 	TAILQ_FOREACH(ev, &base->eventqueue, ev_next) {
 		EVUTIL_ASSERT(ev->ev_flags & EVLIST_INSERTED);
 		EVUTIL_ASSERT(ev->ev_flags & EVLIST_INIT);
@@ -848,6 +889,7 @@ evmap_check_integrity(struct event_base *base)
 		}
 	}
 
+#endif
 	EVUTIL_ASSERT(nio == 0);
 	EVUTIL_ASSERT(nsignals == 0);
 	/* There is no "EVUTIL_ASSERT(ntimers == 0)": eventqueue is only for

include/event2/event_struct.h

@@ -96,7 +96,9 @@ struct {								\
 struct event_base;
 struct event {
 	TAILQ_ENTRY(event) ev_active_next;
+#ifdef _EVENT_USE_EVENTLIST
 	TAILQ_ENTRY(event) ev_next;
+#endif
 	/* for managing timeouts */
 	union {
 		TAILQ_ENTRY(event) ev_next_with_common_timeout;