MM-30140 LRU critical section optimization (#16184)

* MM-30140 LRU critical section optimization

* Remove empty line

* Renamed lru function

services/cache/lru.go

@@ -79,16 +79,12 @@ func (l *LRU) SetWithDefaultExpiry(key string, value interface{}) error {
 // SetWithExpiry adds the given key and value to the cache with the given expiry. If the key
 // already exists, it will overwrite the previoous value
 func (l *LRU) SetWithExpiry(key string, value interface{}, ttl time.Duration) error {
-	l.lock.Lock()
-	defer l.lock.Unlock()
 	return l.set(key, value, ttl)
 }
 
 // Get the content stored in the cache for the given key, and decode it into the value interface.
 // return ErrKeyNotFound if the key is missing from the cache
 func (l *LRU) Get(key string, value interface{}) error {
-	l.lock.Lock()
-	defer l.lock.Unlock()
 	return l.get(key, value)
 }
 
@@ -160,6 +156,9 @@ func (l *LRU) set(key string, value interface{}, ttl time.Duration) error {
 		}
 	}
 
+	l.lock.Lock()
+	defer l.lock.Unlock()
+
 	// Check for existing item, ignoring expiry since we'd update anyway.
 	if ent, ok := l.items[key]; ok {
 		l.evictList.MoveToFront(ent)
@@ -186,16 +185,11 @@ func (l *LRU) set(key string, value interface{}, ttl time.Duration) error {
 }
 
 func (l *LRU) get(key string, value interface{}) error {
-	if ent, ok := l.items[key]; ok {
-		e := ent.Value.(*entry)
-
-		if e.generation != l.currentGeneration || (!e.expires.IsZero() && time.Now().After(e.expires)) {
-			l.removeElement(ent)
-			return ErrKeyNotFound
+	e, err := l.getItem(key)
+	if err != nil {
+		return err
 	}
 
-		l.evictList.MoveToFront(ent)
-
 	// We use a fast path for hot structs.
 	if msgpVal, ok := value.(msgp.Unmarshaler); ok {
 		_, err := msgpVal.UnmarshalMsg(e.value)
@@ -231,7 +225,22 @@ func (l *LRU) get(key string, value interface{}) error {
 	// Slow path for other structs.
 	return msgpack.Unmarshal(e.value, value)
 }
-	return ErrKeyNotFound
+
+func (l *LRU) getItem(key string) (*entry, error) {
+	l.lock.Lock()
+	defer l.lock.Unlock()
+
+	ent, ok := l.items[key]
+	if !ok {
+		return nil, ErrKeyNotFound
+	}
+	e := ent.Value.(*entry)
+	if e.generation != l.currentGeneration || (!e.expires.IsZero() && time.Now().After(e.expires)) {
+		l.removeElement(ent)
+		return nil, ErrKeyNotFound
+	}
+	l.evictList.MoveToFront(ent)
+	return e, nil
 }
 
 func (l *LRU) removeElement(e *list.Element) {