add write lock for cache#Get

Author: zhengchun

cache.go

@@ -16,9 +16,9 @@ var DisableSelectorCache = false
 var SelectorCacheMaxEntries = 50
 
 var (
-	cacheOnce sync.Once
-	cache     *lru.Cache
-	cacheMutex sync.RWMutex
+	cacheOnce  sync.Once
+	cache      *lru.Cache
+	cacheMutex sync.Mutex
 )
 
 func getQuery(expr string) (*xpath.Expr, error) {
@@ -28,14 +28,11 @@ func getQuery(expr string) (*xpath.Expr, error) {
 	cacheOnce.Do(func() {
 		cache = lru.New(SelectorCacheMaxEntries)
 	})
-	cacheMutex.RLock()
+	cacheMutex.Lock()
+	defer cacheMutex.Unlock()
 	if v, ok := cache.Get(expr); ok {
-		cacheMutex.RUnlock()
 		return v.(*xpath.Expr), nil
 	}
-	cacheMutex.RUnlock()
-	cacheMutex.Lock()
-	defer cacheMutex.Unlock()
 	v, err := xpath.Compile(expr)
 	if err != nil {
 		return nil, err