Add functions for collecting high-water counters

Add {isc,ns}_stats_{update_if_greater,get_counter}() functions that
are used to set and collect high-water type of statistics.

(cherry picked from commit a544e2e3)

lib/isc/include/isc/stats.h

@@ -132,6 +132,31 @@ isc_stats_set(isc_stats_t *stats, uint64_t val,
  *\li	'stats' is a valid isc_stats_t.
  */
 
+void isc_stats_update_if_greater(isc_stats_t *stats,
+				 isc_statscounter_t counter,
+				 isc_statscounter_t value);
+/*%<
+* Atomically assigns 'value' to 'counter' if value > counter.
+*
+* Requires:
+*\li	'stats' is a valid isc_stats_t.
+*
+*\li	counter is less than the maximum available ID for the stats specified
+*	on creation.
+*/
+
+isc_statscounter_t
+isc_stats_get_counter(isc_stats_t *stats, isc_statscounter_t counter);
+/*%<
+ * Returns value currently stored in counter.
+ *
+ * Requires:
+ *\li	'stats' is a valid isc_stats_t.
+ *
+ *\li	counter is less than the maximum available ID for the stats specified
+ *	on creation.
+ */
+
 ISC_LANG_ENDDECLS
 
 #endif /* ISC_STATS_H */

lib/isc/stats.c

@@ -151,3 +151,34 @@ isc_stats_set(isc_stats_t *stats, uint64_t val,
 	atomic_store_explicit(&stats->counters[counter], val,
 			      memory_order_relaxed);
 }
+
+void isc_stats_update_if_greater(isc_stats_t *stats,
+				 isc_statscounter_t counter,
+				 isc_statscounter_t value)
+{
+	REQUIRE(ISC_STATS_VALID(stats));
+	REQUIRE(counter < stats->ncounters);
+
+	isc_statscounter_t curr_value;
+
+	do {
+		curr_value = atomic_load_explicit(&stats->counters[counter],
+						  memory_order_relaxed);
+		if (curr_value >= value) {
+			break;
+		}
+
+	} while (!atomic_compare_exchange_strong(&stats->counters[counter],
+						 &curr_value,
+						 value));
+}
+
+isc_statscounter_t
+isc_stats_get_counter(isc_stats_t *stats, isc_statscounter_t counter)
+{
+	REQUIRE(ISC_STATS_VALID(stats));
+	REQUIRE(counter < stats->ncounters);
+
+	return (atomic_load_explicit(&stats->counters[counter],
+				    memory_order_relaxed));
+}

lib/isc/win32/libisc.def.in

@@ -539,9 +539,11 @@ isc_stats_create
 isc_stats_decrement
 isc_stats_detach
 isc_stats_dump
+isc_stats_get_counter
 isc_stats_increment
 isc_stats_ncounters
 isc_stats_set
+isc_stats_update_if_greater
 isc_stdio_close
 isc_stdio_flush
 isc_stdio_open

lib/ns/include/ns/stats.h

@@ -123,4 +123,11 @@ ns_stats_decrement(ns_stats_t *stats, isc_statscounter_t counter);
 isc_stats_t *
 ns_stats_get(ns_stats_t *stats);
 
+void ns_stats_update_if_greater(ns_stats_t *stats,
+				isc_statscounter_t counter,
+				isc_statscounter_t value);
+
+isc_statscounter_t
+ns_stats_get_counter(ns_stats_t *stats, isc_statscounter_t counter);
+
 #endif /* NS_STATS_H */

lib/ns/stats.c

@@ -123,3 +123,20 @@ ns_stats_get(ns_stats_t *stats) {
 
 	return (stats->counters);
 }
+
+void ns_stats_update_if_greater(ns_stats_t *stats,
+			     isc_statscounter_t counter,
+			     isc_statscounter_t value)
+{
+	REQUIRE(NS_STATS_VALID(stats));
+
+	isc_stats_update_if_greater(stats->counters, counter, value);
+}
+
+isc_statscounter_t
+ns_stats_get_counter(ns_stats_t *stats, isc_statscounter_t counter)
+{
+	REQUIRE(NS_STATS_VALID(stats));
+
+	return (isc_stats_get_counter(stats->counters, counter));
+}

lib/ns/win32/libns.def

@@ -102,6 +102,8 @@ ns_stats_create
 ns_stats_decrement
 ns_stats_detach
 ns_stats_get
+ns_stats_get_counter
 ns_stats_increment
+ns_stats_update_if_greater
 ns_update_start
 ns_xfr_start