✨ feat: Day2 单机并发缓存

.gitignore

@@ -1,2 +1,4 @@
+.draft/
+
 *.jpg
 *.png

byteview.go

@@ -0,0 +1,26 @@
+package geecache
+
+type ByteView struct {
+ b []byte
+}
+
+func (v ByteView) Len() int {
+ return len(v.b)
+}
+
+// ByteSlice 返回字节数组形式的拷贝
+//
+// b 是只读的，返回拷贝防止缓存值被外部程序修改
+func (v ByteView) ByteSlice() []byte {
+ return cloneBytes(v.b)
+}
+
+func (v ByteView) String() string {
+ return string(v.b)
+}
+
+func cloneBytes(b []byte) []byte {
+ c := make([]byte, len(b))
+ copy(c, b)
+ return c
+}

cache.go

@@ -0,0 +1,38 @@
+package geecache
+
+import (
+ "geecache/lru"
+ "sync"
+)
+
+type cache struct {
+ mu sync.Mutex
+ lru *lru.Cache
+ cacheBytes int64
+}
+
+// add
+//
+// 使用延迟初始化
+func (c *cache) add(key string, value ByteView) {
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ if c.lru == nil {
+ c.lru = lru.New(c.cacheBytes, nil)
+ }
+ c.lru.Add(key, value)
+}
+
+func (c *cache) get(key string) (value ByteView, ok bool) {
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ if c.lru == nil {
+ return
+ }
+
+ if v, ok := c.lru.Get(key); ok {
+ return v.(ByteView), ok
+ }
+
+ return
+}

geecache.go

@@ -0,0 +1,91 @@
+package geecache
+
+import (
+ "fmt"
+ "log"
+ "sync"
+)
+
+// 接口型函数
+//
+// 参考 Go 语言标准库 net/http/server.go
+type Getter interface {
+ Get(key string) ([]byte, error)
+}
+
+type GetterFunc func(key string) ([]byte, error)
+
+func (f GetterFunc) Get(key string) ([]byte, error) {
+ return f(key)
+}
+
+// Group 缓存命名空间
+//
+// getter Getter 缓存未命中时获取源数据的回调
+//
+// A Group is a cache namespace and associated data loaded spread over
+type Group struct {
+ name string
+ getter Getter
+ mainCache cache
+}
+
+var (
+ mu sync.RWMutex
+ groups = make(map[string]*Group)
+)
+
+func NewGroup(name string, cacheBytes int64, getter Getter) *Group {
+ if getter == nil {
+ panic("nil Getter")
+ }
+ mu.Lock()
+ defer mu.Unlock()
+ g := &Group{
+ name: name,
+ getter: getter,
+ mainCache: cache{cacheBytes: cacheBytes},
+ }
+ groups[name] = g // 其实只需要对 map 加锁
+ return g
+}
+
+// GetGroup returns the named group previously created with NewGroup, or
+// nil if there's no such group.
+func GetGroup(name string) *Group {
+ mu.RLock()
+ g := groups[name]
+ mu.RUnlock()
+ return g
+}
+
+func (g *Group) Get(key string) (ByteView, error) {
+ if key == "" {
+ return ByteView{}, fmt.Errorf("key is required")
+ }
+
+ if v, ok := g.mainCache.get(key); ok {
+ log.Println("[GeeCache] hit")
+ return v, nil
+ }
+
+ return g.load(key)
+}
+
+func (g *Group) load(key string) (value ByteView, err error) {
+ return g.getLocally(key)
+}
+
+func (g *Group) getLocally(key string) (ByteView, error) {
+ bytes, err := g.getter.Get(key)
+ if err != nil {
+ return ByteView{}, err
+ }
+ value := ByteView{b: cloneBytes(bytes)}
+ g.populateCache(key, value)
+ return value, err
+}
+
+func (g *Group) populateCache(key string, value ByteView) {
+ g.mainCache.add(key, value)
+}

geecache_test.go

@@ -0,0 +1,60 @@
+package geecache
+
+import (
+ "fmt"
+ "log"
+ "reflect"
+ "testing"
+)
+
+func TestGetter(t *testing.T) {
+ var f Getter = GetterFunc(func(key string) ([]byte, error) {
+ return []byte(key), nil
+ })
+
+ expect := []byte("key")
+ if v, _ := f.Get("key"); !reflect.DeepEqual(v, expect) {
+ t.Fatalf("callback failed")
+ }
+}
+
+var db = map[string]string{
+ "Tom": "630",
+ "Jack": "589",
+ "Sam": "567",
+}
+
+// 1、在缓存为空的情况下，能够通过回调函数获取到源数据。
+// 2、在缓存已经存在的情况下，是否直接从缓存中获取，
+// 为了实现这一点，使用 loadCounts 统计某个键调用回调函数的次数，
+// 如果次数大于1，则表示调用了多次回调函数，没有缓存。
+// go test -run TestGet
+func TestGet(t *testing.T) {
+ loadCounts := make(map[string]int, len(db))
+ gee := NewGroup("scores", 2<<10, GetterFunc(
+ func(key string) ([]byte, error) {
+ log.Println("[SlowDB] search key", key)
+ if v, ok := db[key]; ok {
+ if _, ok := loadCounts[key]; !ok {
+ loadCounts[key] = 0
+ }
+ loadCounts[key] += 1
+ return []byte(v), nil
+ }
+ return nil, fmt.Errorf("%s not exist", key)
+ },
+ ))
+
+ for k, v := range db {
+ if view, err := gee.Get(k); err != nil || view.String() != v {
+ t.Fatalf("failed to get value of Tom")
+ } // loaded from callback function
+ if _, err := gee.Get(k); err != nil || loadCounts[k] > 1 {
+ t.Fatalf("cache %s miss", k)
+ } // cache hit
+ }
+
+ if view, err := gee.Get("unknown"); err == nil {
+ t.Fatalf("the value of unknown should be empty, but %s got", view)
+ }
+}