From 7c3b61bb097738888285a685cc01f87880b834e6 Mon Sep 17 00:00:00 2001
From: Jesper Jensen <jesper@jnsn.dev>
Date: Sun, 4 May 2025 15:37:24 +0200
Subject: Add metric to track next hash expire

---
 src/metrics.c | 10 ++++++++++
 src/metrics.h |  1 +
 src/peers.c   | 16 ++++++++++++----
 3 files changed, 23 insertions(+), 4 deletions(-)

(limited to 'src')

diff --git a/src/metrics.c b/src/metrics.c
index de39cdb..eb50f09 100644
--- a/src/metrics.c
+++ b/src/metrics.c
@@ -11,6 +11,7 @@ prom_counter_t *peers = NULL;
 prom_gauge_t *current_hashes = NULL;
 prom_counter_t *hashes = NULL;
 prom_counter_t *hash_expired = NULL;
+prom_gauge_t *hash_next_expire = NULL;
 prom_counter_t *queries = NULL;
 prom_counter_t *requests = NULL;
 prom_histogram_t *offered = NULL;
@@ -140,6 +141,15 @@ void metric_init() {
 		)
 	);
 
+	hash_next_expire = prom_collector_registry_must_register_metric(
+		prom_gauge_new(
+			"dht_hashes_next_expire",
+			"Next time a hash expires",
+			0,
+			NULL
+		)
+	);
+
 	queries = prom_collector_registry_must_register_metric(
 		prom_counter_new(
 			"dht_queries_total",
diff --git a/src/metrics.h b/src/metrics.h
index 4455800..309177c 100644
--- a/src/metrics.h
+++ b/src/metrics.h
@@ -13,6 +13,7 @@ extern prom_counter_t *peers;
 extern prom_gauge_t *current_hashes;
 extern prom_counter_t *hashes;
 extern prom_counter_t *hash_expired;
+extern prom_gauge_t *hash_next_expire;
 extern prom_counter_t *queries;
 extern prom_counter_t *requests;
 extern prom_histogram_t *offered;
diff --git a/src/peers.c b/src/peers.c
index d320e30..f9477c6 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -130,8 +130,7 @@ int add_peer(struct infohash* infohash, struct addr* peer, time_t now) {
 	peer_status.peers++;
 	prom_counter_inc(peers, NULL);
 
-	prom_gauge_set(current_hashes, (double)peer_table_load, NULL);
-
+	peer_update_metrics();
 	check_duplicates();
 	return 0;
 }
@@ -151,12 +150,18 @@ void get_peers(struct infohash* infohash, struct addr **peers, size_t *peers_len
 }
 
 void expire_hashes(time_t now) {
+	time_t next_expire = -1;
+
 	assert(peer_table_load < peer_table_size);
 	for(size_t i = 0; i < peer_table_size; i++) {
 		struct peer_entry *entry = &peer_table[i];
 		if(!entry->set) continue;
 
-		if(difftime(now, entry->last_seen + HASH_TIMEOUT) < 0.0) continue;
+		time_t entry_expire = entry->last_seen + HASH_TIMEOUT;
+		if(difftime(now, entry_expire) < 0.0) {
+			next_expire = entry_expire < next_expire ? entry_expire : next_expire;
+			continue;
+		}
 
 		// Find the last hash that collides with us
 		uint64_t entry_hash = hash(&entry->key, peer_table_size);
@@ -187,8 +192,9 @@ void expire_hashes(time_t now) {
 		prom_counter_inc(hash_expired, NULL);
 	}
 
+	prom_gauge_set(hash_next_expire, next_expire, NULL);
+	peer_update_metrics();
 	check_duplicates();
-	prom_gauge_set(current_hashes, (double)peer_table_load, NULL);
 }
 
 void peer_update_metrics() {
@@ -197,4 +203,6 @@ void peer_update_metrics() {
 		if(peer_table[i].set) continue;
 		if(now < peer_table[i].last_seen) dbg("%d was seen after now? (%ld < %ld)", i, now, peer_table[i].last_seen);
 	}
+
+	prom_gauge_set(current_hashes, (double)peer_table_load, NULL);
 }
-- 
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