Fix bug with LRU implementation

2-race-in-cache/check_test.go

@@ -6,7 +6,10 @@
 
 package main
 
-import "testing"
+import (
+	"strconv"
+	"testing"
+)
 
 func TestMain(t *testing.T) {
 	cache := run()
@@ -20,3 +23,24 @@ func TestMain(t *testing.T) {
 		t.Errorf("Incorrect pages size %v", pagesLen)
 	}
 }
+
+func TestLRU(t *testing.T) {
+	loader := Loader{
+		DB: GetMockDB(),
+	}
+	cache := New(&loader)
+
+	for i := 0; i < 100; i++ {
+		cache.Get("Test " + strconv.Itoa(i))
+	}
+
+	if len(cache.cache) != 100 {
+		t.Errorf("cache not 100: %d", len(cache.cache))
+	}
+	cache.Get("Test 0")
+	cache.Get("Test 101")
+	if _, ok := cache.cache["Test 0"]; !ok {
+		t.Errorf("0 evicted incorrectly: %v", cache.cache)
+	}
+
+}

2-race-in-cache/main.go

@@ -19,9 +19,14 @@ type KeyStoreCacheLoader interface {
 	Load(string) string
 }
 
+type Page struct {
+	Key   string
+	Value string
+}
+
 // KeyStoreCache is a LRU cache for string key-value pairs
 type KeyStoreCache struct {
-	cache map[string]string
+	cache map[string]*list.Element
 	pages list.List
 	load  func(string) string
 }
@@ -30,28 +35,30 @@ type KeyStoreCache struct {
 func New(load KeyStoreCacheLoader) *KeyStoreCache {
 	return &KeyStoreCache{
 		load:  load.Load,
-		cache: make(map[string]string),
+		cache: make(map[string]*list.Element),
 	}
 }
 
 // Get gets the key from cache, loads it from the source if needed
 func (k *KeyStoreCache) Get(key string) string {
-	val, ok := k.cache[key]
-
-	// Miss - load from database and save it in cache
-	if !ok {
-		val = k.load(key)
-		k.cache[key] = val
-		k.pages.PushFront(key)
-
+	if e, ok := k.cache[key]; ok {
+		k.pages.MoveToFront(e)
+		return e.Value.(Page).Value
+	} else {
+		// Miss - load from database and save it in cache
+		page := Page{key, k.load(key)}
 		// if cache is full remove the least used item
-		if len(k.cache) > CacheSize {
-			delete(k.cache, k.pages.Back().Value.(string))
-			k.pages.Remove(k.pages.Back())
+		if len(k.cache) >= CacheSize {
+			end := k.pages.Back()
+			// remove from map
+			delete(k.cache, end.Value.(Page).Key)
+			// remove from list
+			k.pages.Remove(end)
 		}
+		k.pages.PushFront(page)
+		k.cache[key] = k.pages.Front()
+		return page.Value
 	}
-
-	return val
 }
 
 // Loader implements KeyStoreLoader