From 5e8c73c12c2ba637c18e9f79809769116fec4b15 Mon Sep 17 00:00:00 2001
From: Petrichor <390983386@qq.com>
Date: Wed, 30 Mar 2022 15:39:21 +0800
Subject: [PATCH] =?UTF-8?q?=E2=9C=A8=20feat(lru):=20LRU=20=E7=BC=93?=
 =?UTF-8?q?=E5=AD=98=E6=B7=98=E6=B1=B0=E7=AD=96=E7=95=A5?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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Cache New Get RemoveOldest Add Len
---
 .gitignore            |  2 +
 .vscode/settings.json |  3 ++
 go.mod                |  3 ++
 lru/lru.go            | 88 +++++++++++++++++++++++++++++++++++++++++++
 lru/lru_test.go       | 55 +++++++++++++++++++++++++++
 5 files changed, 151 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 .vscode/settings.json
 create mode 100644 go.mod
 create mode 100644 lru/lru.go
 create mode 100644 lru/lru_test.go

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..0a70cd3
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*.jpg
+*.png
\ No newline at end of file
diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000..a460645
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,3 @@
+{
+    "go.inferGopath": false
+}
\ No newline at end of file
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..1f7c52b
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module geecache
+
+go 1.18
diff --git a/lru/lru.go b/lru/lru.go
new file mode 100644
index 0000000..4037638
--- /dev/null
+++ b/lru/lru.go
@@ -0,0 +1,88 @@
+package lru
+
+import (
+	"container/list"
+)
+
+// 核心数据结构
+// map + double linked list
+
+// Cache is a LRU cache. Not safe for ocncurrent access.
+type Cache struct {
+	maxBytes  int64      // 允许的最大内存
+	nbytes    int64      // 已使用内存
+	ll        *list.List // 双向链表
+	cache     map[string]*list.Element
+	OnEvicted func(key string, value Value) // 某条记录被移除时的回调，可以为 nil
+}
+
+type entry struct {
+	key   string
+	value Value
+}
+
+type Value interface {
+	Len() int
+}
+
+// New 实例化
+func New(maxBytes int64, onEvicted func(string, Value)) *Cache {
+	return &Cache{
+		maxBytes:  maxBytes,
+		ll:        list.New(),
+		cache:     make(map[string]*list.Element),
+		OnEvicted: onEvicted,
+	}
+}
+
+// Get 查找
+//
+// 如果键对应的链表结点存在，将对应节点移动到队首，并返回找到的值
+func (c *Cache) Get(key string) (value Value, ok bool) {
+	if ele, ok := c.cache[key]; ok {
+		c.ll.MoveToFront(ele)
+		kv := ele.Value.(*entry)
+		return kv.value, true
+	}
+	return
+}
+
+// RemoveOldest 缓存淘汰
+//
+// 移除最近最少访问的节点（尾节点）
+func (c *Cache) RemoveOldest() {
+	ele := c.ll.Back()
+	if ele != nil {
+		c.ll.Remove(ele)
+		kv := ele.Value.(*entry)
+		//TODO
+		delete(c.cache, kv.key)
+		c.nbytes -= int64(len(kv.key)) + int64(kv.value.Len())
+		if c.OnEvicted != nil {
+			c.OnEvicted(kv.key, kv.value)
+		}
+	}
+}
+
+// Add 添加一个值到缓存中
+func (c *Cache) Add(key string, value Value) {
+	// 已存在，修改值，并将该节点移动到队首
+	if ele, ok := c.cache[key]; ok {
+		c.ll.MoveToFront(ele)
+		kv := ele.Value.(*entry)
+		c.nbytes += int64(value.Len()) - int64(kv.value.Len())
+		kv.value = value
+	} else {
+		ele := c.ll.PushFront(&entry{key, value})
+		c.cache[key] = ele
+		c.nbytes += int64(len(key)) + int64(value.Len())
+	}
+	for c.maxBytes != 0 && c.maxBytes < c.nbytes {
+		c.RemoveOldest()
+	}
+}
+
+// Len 获取已添加数据条数
+func (c *Cache) Len() int {
+	return c.ll.Len()
+}
diff --git a/lru/lru_test.go b/lru/lru_test.go
new file mode 100644
index 0000000..85d3e0b
--- /dev/null
+++ b/lru/lru_test.go
@@ -0,0 +1,55 @@
+package lru
+
+import (
+	"reflect"
+	"testing"
+)
+
+type String string
+
+func (s String) Len() int {
+	return len(s)
+}
+
+func TestGet(t *testing.T) {
+	lru := New(int64(0), nil)
+	lru.Add("key1", String("1234"))
+	if v, ok := lru.Get("key1"); !ok || string(v.(String)) != "1234" {
+		t.Fatalf("cache hit key1=1234 failed")
+	}
+	if _, ok := lru.Get("key2"); ok {
+		t.Fatalf("cache miss key2 failed")
+	}
+}
+
+func TestRemoveOldest(t *testing.T) {
+	k1, k2, k3 := "key1", "key2", "k3"
+	v1, v2, v3 := "value1", "value2", "v3"
+	cap := len(k1 + k2 + v1 + v2)
+	lru := New(int64(cap), nil)
+	lru.Add(k1, String(v1))
+	lru.Add(k2, String(v2))
+	lru.Add(k3, String(v3))
+
+	if _, ok := lru.Get("key1"); ok || lru.Len() != 2 {
+		t.Fatalf("RemoveOldest key1 failed")
+	}
+}
+
+func TestOnEvicted(t *testing.T) {
+	keys := make([]string, 0)
+	callback := func(key string, value Value) {
+		keys = append(keys, key)
+	}
+	lru := New(int64(10), callback)
+	lru.Add("key1", String("123456"))
+	lru.Add("k2", String("k2"))
+	lru.Add("k3", String("k3"))
+	lru.Add("k4", String("k4"))
+
+	expect := []string{"key1", "k2"}
+
+	if !reflect.DeepEqual(expect, keys) {
+		t.Fatalf("Call OnEvicted failed, expect keys equals to %s", expect)
+	}
+}