From e47042fe2604625fffdba015c2a9bdaed30e1f0c Mon Sep 17 00:00:00 2001
From: Nick Mathewson <nickm@torproject.org>
Date: Wed, 2 Feb 2011 20:05:41 -0500
Subject: [PATCH] Optimize the case where we reinsert an existing timeout

---
 event.c            | 36 ++++++++++++++++++++++++++++++++++--
 minheap-internal.h | 18 ++++++++++++++++++
 2 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/event.c b/event.c
index fa8c722d..63927085 100644
--- a/event.c
+++ b/event.c
@@ -133,6 +133,8 @@ static inline int event_del_internal(struct event *ev);
 
 static void	event_queue_insert(struct event_base *, struct event *, int);
 static void	event_queue_remove(struct event_base *, struct event *, int);
+static void	event_queue_reinsert(struct event_base *,struct event *ev,int);
+
 static int	event_haveevents(struct event_base *);
 
 static int	event_process_active(struct event_base *);
@@ -146,6 +148,9 @@ static inline void	event_persist_closure(struct event_base *, struct event *ev);
 
 static int	evthread_notify_base(struct event_base *base);
 
+static void insert_common_timeout_inorder(struct common_timeout_list *ctl,
+    struct event *ev);
+
 #ifndef _EVENT_DISABLE_DEBUG_MODE
 /* These functions implement a hashtable of which 'struct event *' structures
  * have been setup or added.  We don't want to trust the content of the struct
@@ -2030,7 +2035,7 @@ event_add_internal(struct event *ev, const struct timeval *tv,
 			/* XXX I believe this is needless. */
 			if (min_heap_elt_is_top(ev))
 				notify = 1;
-			event_queue_remove(base, ev, EVLIST_TIMEOUT);
+			/*event_queue_remove(base, ev, EVLIST_TIMEOUT);*/
 		}
 
 		/* Check if it is active due to a timeout.  Rescheduling
@@ -2070,7 +2075,8 @@ event_add_internal(struct event *ev, const struct timeval *tv,
 			 "event_add: timeout in %d seconds, call %p",
 			 (int)tv->tv_sec, ev->ev_callback));
 
-		event_queue_insert(base, ev, EVLIST_TIMEOUT);
+		event_queue_reinsert(base, ev, EVLIST_TIMEOUT);
+
 		if (common_timeout) {
 			struct common_timeout_list *ctl =
 			    get_common_timeout_list(base, &ev->ev_timeout);
@@ -2458,6 +2464,32 @@ event_queue_remove(struct event_base *base, struct event *ev, int queue)
 	}
 }
 
+/* Remove and reinsert 'ev' into the appropriate queue.  Only EVLIST_TIMEOUT
+ * is supported. */
+static void
+event_queue_reinsert(struct event_base *base, struct event *ev, int queue)
+{
+	if (!(ev->ev_flags & queue)) {
+		event_queue_insert(base, ev, queue);
+		return;
+	}
+
+	if (queue != EVLIST_TIMEOUT) {
+		event_errx(1, "%s: Unsupported queue %x", __func__, queue);
+		return; /* unreached */
+	}
+
+	if (is_common_timeout(&ev->ev_timeout, base)) {
+		struct common_timeout_list *ctl =
+		    get_common_timeout_list(base, &ev->ev_timeout);
+		TAILQ_REMOVE(&ctl->events, ev,
+		    ev_timeout_pos.ev_next_with_common_timeout);
+		insert_common_timeout_inorder(ctl, ev);
+	} else {
+		min_heap_adjust(&base->timeheap, ev);
+	}
+}
+
 /* Add 'ev' to the common timeout list in 'ev'. */
 static void
 insert_common_timeout_inorder(struct common_timeout_list *ctl,
diff --git a/minheap-internal.h b/minheap-internal.h
index 8055e903..39e3946a 100644
--- a/minheap-internal.h
+++ b/minheap-internal.h
@@ -53,6 +53,7 @@ static inline struct event*  min_heap_top(min_heap_t* s);
 static inline int	     min_heap_reserve(min_heap_t* s, unsigned n);
 static inline int	     min_heap_push(min_heap_t* s, struct event* e);
 static inline struct event*  min_heap_pop(min_heap_t* s);
+static inline int	     min_heap_adjust(min_heap_t *s, struct event* e);
 static inline int	     min_heap_erase(min_heap_t* s, struct event* e);
 static inline void	     min_heap_shift_up_(min_heap_t* s, unsigned hole_index, struct event* e);
 static inline void	     min_heap_shift_down_(min_heap_t* s, unsigned hole_index, struct event* e);
@@ -115,6 +116,23 @@ int min_heap_erase(min_heap_t* s, struct event* e)
 	return -1;
 }
 
+int min_heap_adjust(min_heap_t *s, struct event *e)
+{
+	if (-1 == e->ev_timeout_pos.min_heap_idx) {
+		return min_heap_push(s, e);
+	} else {
+		unsigned parent = (e->ev_timeout_pos.min_heap_idx - 1) / 2;
+		/* The position of e has changed; we shift it up or down
+		 * as needed.  We can't need to do both. */
+		if (e->ev_timeout_pos.min_heap_idx > 0 && min_heap_elem_greater(s->p[parent], e))
+			min_heap_shift_up_(s, e->ev_timeout_pos.min_heap_idx, e);
+		else
+			min_heap_shift_down_(s, e->ev_timeout_pos.min_heap_idx, e);
+		return 0;
+	}
+	return -1;
+}
+
 int min_heap_reserve(min_heap_t* s, unsigned n)
 {
 	if (s->a < n)