From d49f187da6b6ed06a1188007016f789886bf6217 Mon Sep 17 00:00:00 2001
From: old-tom <892955278@qq.com>
Date: Fri, 22 Dec 2023 17:55:50 +0800
Subject: [PATCH] =?UTF-8?q?feat:lru=E5=AE=9E=E7=8E=B0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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---
 lfu/lfu.go   | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 lfu/queue.go | 62 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 140 insertions(+)
 create mode 100644 lfu/lfu.go
 create mode 100644 lfu/queue.go

diff --git a/lfu/lfu.go b/lfu/lfu.go
new file mode 100644
index 0000000..11aa377
--- /dev/null
+++ b/lfu/lfu.go
@@ -0,0 +1,78 @@
+package lfu
+
+import (
+	"cache"
+	"container/heap"
+)
+
+// lfu
+// @Description:LFU，即最少使用，也就是淘汰缓存中访问频率最低的记录。
+// LFU 认为，如果数据过去被访问多次，那么将来被访问的频率也更高。
+// LFU 的实现需要维护一个按照访问次数排序的队列，每次访问，访问次数加 1，队列重新排序，淘汰时选择访问次数最少的即可
+type lfu struct {
+	// 缓存最大容量
+	maxBytes int
+	// 当一个 entry 从缓存中移除时调用该回调函数，默认为 nil
+	onEvicted func(key string, value any)
+	//已使用的字节数，只包括值，key 不算
+	usedBytes int
+	queue     *queue
+	cache     map[string]*entry
+}
+
+func New(maxBytes int, onEvicted func(key string, value any)) cache.Cache {
+	q := make(queue, 0, 1024)
+	return &lfu{
+		maxBytes:  maxBytes,
+		onEvicted: onEvicted,
+		queue:     &q,
+		cache:     make(map[string]*entry),
+	}
+}
+
+func (l *lfu) Set(key string, value any) {
+	if e, ok := l.cache[key]; ok {
+		l.usedBytes = l.usedBytes - cache.CalcLen(e.value) + cache.CalcLen(value)
+		l.queue.update(e, value, e.weight+1)
+	} else {
+		en := &entry{key: key, value: value}
+		//利用堆特性实现排序
+		heap.Push(l.queue, en)
+		l.cache[key] = en
+		l.usedBytes += en.Len()
+		if l.maxBytes > 0 && l.usedBytes > l.maxBytes {
+
+		}
+	}
+}
+
+func (l *lfu) Get(Key string) any {
+	if e, ok := l.cache[Key]; ok {
+		l.queue.update(e, e.value, e.weight+1)
+		return e.value
+	}
+	return nil
+}
+
+func (l *lfu) Del(Key string) {
+	if e, ok := l.cache[Key]; ok {
+		heap.Remove(l.queue, e.index)
+	}
+}
+
+func (l *lfu) DelOldest() {
+
+}
+
+func (l *lfu) Len() int {
+	return 0
+}
+
+func (l *lfu) removeElement(x any) {
+	if x == nil {
+		return
+	}
+	en := x.(*entry)
+	delete(l.cache, en.key)
+	l.usedBytes -= en.Len()
+}
diff --git a/lfu/queue.go b/lfu/queue.go
new file mode 100644
index 0000000..1c6f343
--- /dev/null
+++ b/lfu/queue.go
@@ -0,0 +1,62 @@
+package lfu
+
+import (
+	"cache"
+	"container/heap"
+)
+
+type entry struct {
+	key   string
+	value any
+	//权重或优先级
+	weight int
+	//下标
+	index int
+}
+
+func (e *entry) Len() int {
+	return cache.CalcLen(e.value) + 8
+}
+
+type queue []*entry
+
+// Len
+//
+//	@Description: 长度
+//	@receiver e
+//	@return int
+func (q queue) Len() int {
+	return len(q)
+}
+
+func (q queue) Less(i, j int) bool {
+	return q[i].weight < q[j].weight
+}
+
+func (q queue) Swap(i, j int) {
+	q[i], q[j] = q[j], q[i]
+	q[i].index = i
+	q[j].index = j
+}
+
+func (q *queue) Push(x any) {
+	n := len(*q)
+	en := x.(*entry)
+	en.index = n
+	*q = append(*q, en)
+}
+
+func (q *queue) Pop() any {
+	old := *q
+	n := len(old)
+	en := old[n-1]
+	en.index = -1
+	*q = old[0 : n-1]
+	return en
+}
+
+func (q *queue) update(en *entry, value any, weight int) {
+	en.value = value
+	en.weight = weight
+	heap.Fix(q, en.index)
+}