common/lru: add metered lru variant

This is a drop-in replacement to add metrics to an LRU cache.

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

common/lru/metered_lru.go

@@ -0,0 +1,64 @@
+// Copyright 2026 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package lru
+
+import (
+	"github.com/ethereum/go-ethereum/metrics"
+)
+
+// MeteredCache is an LRU cache exposing hit metrics.
+// This type is safe for concurrent use.
+type MeteredCache[K comparable, V any] struct {
+	Cache[K, V]
+	hit  *metrics.Meter
+	miss *metrics.Meter
+}
+
+// NewMeteredCache creates a new metered LRU cache.
+func NewMeteredCache[K comparable, V any](capacity int, name string) *MeteredCache[K, V] {
+	return &MeteredCache[K, V]{
+		Cache: *NewCache[K, V](capacity),
+		hit:   metrics.NewRegisteredMeter(name+"/hit", nil),
+		miss:  metrics.NewRegisteredMeter(name+"/miss", nil),
+	}
+}
+
+// Contains reports whether the given key exists in the cache.
+func (c *MeteredCache[K, V]) Contains(key K) bool {
+	ret := c.Cache.Contains(key)
+	if c.hit != nil && c.miss != nil {
+		if ret {
+			c.hit.Mark(1)
+		} else {
+			c.miss.Mark(1)
+		}
+	}
+	return ret
+}
+
+// Get retrieves a value from the cache. This marks the key as recently used.
+func (c *MeteredCache[K, V]) Get(key K) (value V, ok bool) {
+	ret, ok := c.Cache.Get(key)
+	if c.hit != nil && c.miss != nil {
+		if ok {
+			c.hit.Mark(1)
+		} else {
+			c.miss.Mark(1)
+		}
+	}
+	return ret, ok
+}