Fix LRU.Purge (#53)

* fix LRU.Purge, add test

* revise test

---------

Co-authored-by: Tim Rühsen <tim.ruehsen@gmx.de>

lru.go

@@ -526,7 +526,8 @@ func (lru *LRU[K, V]) Keys() []K {
 // The evict function is called for each expired item.
 // The LRU metrics are reset.
 func (lru *LRU[K, V]) Purge() {
-	for i := uint32(0); i < lru.len; i++ {
+	l := lru.len
+	for i := uint32(0); i < l; i++ {
 		_, _, _ = lru.RemoveOldest()
 	}
 
@@ -536,7 +537,8 @@ func (lru *LRU[K, V]) Purge() {
 // PurgeExpired purges all expired items from the LRU.
 // The evict function is called for each expired item.
 func (lru *LRU[K, V]) PurgeExpired() {
-	for i := uint32(0); i < lru.len; i++ {
+	l := lru.len
+	for i := uint32(0); i < l; i++ {
 		pos := lru.elements[lru.head].next
 		if lru.elements[pos].expire != 0 {
 			if lru.elements[pos].expire > now() {

lru_test.go

@@ -141,6 +141,19 @@ func TestSyncedLRU_Add(t *testing.T) {
 	FatalIf(t, cache.Add(3, 4) == false || evictCounter != 1, "Missing eviction")
 }
 
+func TestLRU_Purge(t *testing.T) {
+	evictCounter := uint64(0)
+	cache := makeCache(t, 3, &evictCounter)
+
+	FatalIf(t, cache.Add(1, 2) == true || evictCounter != 0, "Unexpected eviction")
+	FatalIf(t, cache.Add(3, 4) == true || evictCounter != 0, "Unexpected eviction")
+	FatalIf(t, cache.Add(4, 5) == true || evictCounter != 0, "Unexpected eviction")
+	FatalIf(t, cache.Len() != 3, "Unexpected length")
+
+	cache.Purge()
+	FatalIf(t, cache.Len() != 0, "Unexpected length")
+}
+
 func TestLRU_Remove(t *testing.T) {
 	evictCounter := uint64(0)
 	cache := makeCache(t, 2, &evictCounter)