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Easy Redis Java client and Real-Time Data Platform. Valkey compatible. Sync/Async/RxJava3/Reactive API. Client side caching. Over 50 Redis based Java objects and services: JCache API, Apache Tomcat, Hibernate, Spring, Set, Multimap, SortedSet, Map, List, Queue, Deque, Semaphore, Lock, AtomicLong, Map Reduce, Bloom filter, Scheduler, RPC

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/**
 * Copyright (c) 2013-2024 Nikita Koksharov
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.redisson.cache;

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.atomic.AtomicLong;

/**
 * LRU (least recently used) cache.
 * 
 * @author Nikita Koksharov
 *
 * @param  key
 * @param  value
 */
public class LRUCacheMap extends AbstractCacheMap {

    static class OrderedSet {

        final Queue queue = new ConcurrentLinkedQueue<>();
        final Set set = Collections.newSetFromMap(new ConcurrentHashMap<>());

        void add(V element) {
            if (set.add(element)) {
                queue.add(element);
            }
        }

        boolean remove(V element) {
            if (set.remove(element)) {
                queue.remove(element);
                return true;
            }
            return false;
        }

        V removeFirst() {
            while (true) {
                V v = queue.poll();
                if (v != null) {
                    if (set.remove(v)) {
                        return v;
                    }
                } else {
                    return v;
                }
            }
        }

        void clear() {
            set.clear();
            queue.clear();
        }

    }

    private final AtomicLong index = new AtomicLong();
    private final List>> queues = new ArrayList<>();

    public LRUCacheMap(int size, long timeToLiveInMillis, long maxIdleInMillis) {
        super(size, timeToLiveInMillis, maxIdleInMillis);

        for (int i = 0; i < Runtime.getRuntime().availableProcessors()*2; i++) {
            queues.add(new OrderedSet<>());
        }
    }

    @Override
    protected void onValueCreate(CachedValue value) {
        OrderedSet> queue = getQueue(value);
        queue.add(value);
    }

    private OrderedSet> getQueue(CachedValue value) {
        return queues.get(Math.abs(value.hashCode() % queues.size()));
    }

    @Override
    protected void onValueRemove(CachedValue value) {
        OrderedSet> queue = getQueue(value);
        queue.remove(value);
        super.onValueRemove(value);
    }

    @Override
    protected void onValueRead(CachedValue value) {
        OrderedSet> queue = getQueue(value);
        // move value to the tail of the queue
        if (queue.remove(value)) {
            queue.add(value);
        }
    }

    @Override
    protected void onMapFull() {
        int startIndex = -1;
        while (true) {
            int queueIndex = (int) Math.abs(index.incrementAndGet() % queues.size());
            if (queueIndex == startIndex) {
                return;
            }
            if (startIndex == -1) {
                startIndex = queueIndex;
            }

            OrderedSet> queue = queues.get(queueIndex);
            CachedValue removedValue = queue.removeFirst();
            if (removedValue != null) {
                if (map.remove(removedValue.getKey(), removedValue)) {
                    super.onValueRemove(removedValue);
                }
                return;
            }
        }
    }

    @Override
    public void clear() {
        for (OrderedSet> collection : queues) {
            collection.clear();
        }
        super.clear();
    }

}