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 with better
performance. Here is an example.
```
public class LRUCache<K, V> {
private final int capacity;
private ConcurrentMap<K, V> cache;
private ConcurrentLinkedDeque<K> keys;
private final ReentrantReadWriteLock lock;
public LRUCache(int capacity) {
this.capacity = capacity;
this.cache = new ConcurrentHashMap<>(capacity);
this.keys = new ConcurrentLinkedDeque<>();
this.lock = new ReentrantReadWriteLock();
}
public V get(K key) {
lock.readLock().lock();
try {
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;
} finally {
lock.readLock().unlock();
}
}
public void put(K key, V value) {
lock.writeLock().lock();
try {
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);
} finally {
lock.writeLock().unlock();
}
}
}
```
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