From 09e4fb2ffaeaccf6c74c5aeac7ffa65fc6743b1a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ayd=C4=B1n=20Mercan?= <aydin@isc.org>
Date: Tue, 30 Apr 2024 14:37:26 +0300
Subject: [PATCH] Return the old counter value in `isc_stats_increment`

Returning the value allows for better high-water tracking without
running into edge cases like the following:

0. The counter is at value X
1. Increment the value (X+1)
2. The value is decreased multiple times in another threads (X+1-Y)
3. Get the value (X+1-Y)
4. Update-if-greater misses the X+1 value which should have been the
   high-water
---
 lib/isc/include/isc/stats.h | 4 ++--
 lib/isc/stats.c             | 4 ++--
 lib/ns/include/ns/stats.h   | 2 +-
 lib/ns/stats.c              | 4 ++--
 4 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/lib/isc/include/isc/stats.h b/lib/isc/include/isc/stats.h
index 23a076eba9..f6520969c8 100644
--- a/lib/isc/include/isc/stats.h
+++ b/lib/isc/include/isc/stats.h
@@ -137,10 +137,10 @@ isc_stats_ncounters(isc_stats_t *stats);
  *
  */
 
-void
+isc_statscounter_t
 isc_stats_increment(isc_stats_t *stats, isc_statscounter_t counter);
 /*%<
- * Increment the counter-th counter of stats.
+ * Increment the counter-th counter of stats and return the old value.
  *
  * Requires:
  *\li	'stats' is a valid isc_stats_t.
diff --git a/lib/isc/stats.c b/lib/isc/stats.c
index 07a88fb6c9..2f7e8bcde1 100644
--- a/lib/isc/stats.c
+++ b/lib/isc/stats.c
@@ -97,12 +97,12 @@ isc_stats_create(isc_mem_t *mctx, isc_stats_t **statsp, int ncounters) {
 	*statsp = stats;
 }
 
-void
+isc_statscounter_t
 isc_stats_increment(isc_stats_t *stats, isc_statscounter_t counter) {
 	REQUIRE(ISC_STATS_VALID(stats));
 	REQUIRE(counter < stats->ncounters);
 
-	atomic_fetch_add_relaxed(&stats->counters[counter], 1);
+	return (atomic_fetch_add_relaxed(&stats->counters[counter], 1));
 }
 
 void
diff --git a/lib/ns/include/ns/stats.h b/lib/ns/include/ns/stats.h
index d7e79443cf..c904d7f38c 100644
--- a/lib/ns/include/ns/stats.h
+++ b/lib/ns/include/ns/stats.h
@@ -124,7 +124,7 @@ ns_stats_detach(ns_stats_t **statsp);
 void
 ns_stats_create(isc_mem_t *mctx, int ncounters, ns_stats_t **statsp);
 
-void
+isc_statscounter_t
 ns_stats_increment(ns_stats_t *stats, isc_statscounter_t counter);
 
 void
diff --git a/lib/ns/stats.c b/lib/ns/stats.c
index 84dd0ab029..791c08a756 100644
--- a/lib/ns/stats.c
+++ b/lib/ns/stats.c
@@ -78,11 +78,11 @@ ns_stats_create(isc_mem_t *mctx, int ncounters, ns_stats_t **statsp) {
 /*%
  * Increment/Decrement methods
  */
-void
+isc_statscounter_t
 ns_stats_increment(ns_stats_t *stats, isc_statscounter_t counter) {
 	REQUIRE(NS_STATS_VALID(stats));
 
-	isc_stats_increment(stats->counters, counter);
+	return (isc_stats_increment(stats->counters, counter));
 }
 
 void