boicehuang commented on code in PR #13306:
URL: https://github.com/apache/lucene/pull/13306#discussion_r1579596679


##########
lucene/core/src/java/org/apache/lucene/search/LRUQueryCache.java:
##########
@@ -265,7 +269,6 @@ boolean requiresEviction() {
   }
 
   CacheAndCount get(Query key, IndexReader.CacheHelper cacheHelper) {
-    assert lock.isHeldByCurrentThread();
     assert key instanceof BoostQuery == false;
     assert key instanceof ConstantScoreQuery == false;
     final IndexReader.CacheKey readerKey = cacheHelper.getKey();

Review Comment:
   but I don't think it is the best to use `Collections.synchronizedMap`,  we 
can use `ConcurrentLinkedDeque` to achieve LRU expiration better. Here is an 
example.
   ```
   public class LRUCache<K, V> {
       private final int capacity;
       private ConcurrentMap<K, V> cache;
       private ConcurrentLinkedDeque<K> keys;
   
       public LRUCache(int capacity) {
           this.capacity = capacity;
           this.cache = new ConcurrentHashMap<>(capacity);
           this.keys = new ConcurrentLinkedDeque<>();
       }
   
       public V get(K key) {
           V value = cache.get(key);
           if (value != null) {
               keys.remove(key); // remove first occurrence of key
               keys.addFirst(key); // add key to the head
           }
           return value;
       }
   
       public void put(K key, V value) {
           if (cache.containsKey(key)) {
               keys.remove(key); // remove first occurrence of key
           }
   
           while (keys.size() >= capacity) {
               K lastKey = keys.removeLast();
               if (lastKey != null) {
                   cache.remove(lastKey);
               }
           }
   
           cache.put(key, value);
           keys.addFirst(key);
       }
   }
   ```



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