lru cache abandoned linked list version

runtime/lrucache.go

@@ -0,0 +1,66 @@
+// Copyright Suneido Software Corp. All rights reserved.
+// Governed by the MIT license found in the LICENSE file.
+
+package runtime
+
+type LruCache struct {
+	size int
+	hm    Hmap
+	getfn func(Value) Value
+	// entry is the head/tail of the lru link list.
+	// The values are not used.
+	entry
+}
+
+type entry struct {
+	Value
+	key Value
+	next *entry
+	prev *entry
+}
+
+var _ Value = (*entry)(nil)
+
+func NewLruCache(size int, getfn func(Value) Value) *LruCache {
+	lru := &LruCache{size: size, getfn: getfn}
+	lru.next = &lru.entry
+	lru.prev = &lru.entry
+	return lru
+}
+
+func (lru *LruCache) Get(key Value) Value {
+	e := lru.hm.Get(key).(*entry)
+	if e != nil { // in cache
+		lru.moveToFront(e)
+		return e.Value
+	}
+	// not in cache
+	if lru.hm.Size() > lru.size {
+		// discard oldest (lru.prev)
+		lru.hm.Del(lru.prev.key)
+		lru.unlink(lru.prev)
+	}
+	// get/calc it and add it
+	val := lru.getfn(key)
+	e = &entry{Value: val, key: key}
+	lru.hm.Put(key, e)
+	lru.insert(e)
+	return val
+}
+
+func (lru *LruCache) moveToFront(e *entry) {
+	lru.unlink(e)
+	lru.insert(e)
+}
+
+func (lru *LruCache) unlink(e *entry) {
+	e.prev.next = e.next
+	e.next.prev = e.prev
+}
+
+func (lru *LruCache) insert(e *entry) {
+	e.prev = &lru.entry
+	e.next = lru.next
+	e.next.prev = e
+	lru.next = e
+}