content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.client.file.cache.evictor;
  
  import alluxio.client.file.cache.PageId;
  
  import java.util.Collections;
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.function.Predicate;
  import javax.annotation.Nullable;
  import javax.annotation.concurrent.ThreadSafe;
  
  /**
   * LRU client-side cache eviction policy.
   */
  @ThreadSafe
  public class LRUCacheEvictor implements CacheEvictor {
    private static final int LINKED_HASH_MAP_INIT_CAPACITY = 200;
    private static final float LINKED_HASH_MAP_INIT_LOAD_FACTOR = 0.75f;
    private static final boolean LINKED_HASH_MAP_ACCESS_ORDERED = true;
    private static final boolean UNUSED_MAP_VALUE = true;
  
    // TODO(feng): unify with worker side evictor
    protected final Map<PageId, Boolean> mLRUCache =
        Collections.synchronizedMap(new LinkedHashMap<>(LINKED_HASH_MAP_INIT_CAPACITY,
            LINKED_HASH_MAP_INIT_LOAD_FACTOR, LINKED_HASH_MAP_ACCESS_ORDERED));
  
    /**
     * Constructor.
     * @param options
     */
    public LRUCacheEvictor(CacheEvictorOptions options) {
    }
  
    @Override
    public void updateOnGet(PageId pageId) {
      mLRUCache.put(pageId, UNUSED_MAP_VALUE);
    }
  
    @Override
    public void updateOnPut(PageId pageId) {
      mLRUCache.put(pageId, UNUSED_MAP_VALUE);
    }
  
    @Override
    public void updateOnDelete(PageId pageId) {
      mLRUCache.remove(pageId, UNUSED_MAP_VALUE);
    }
  
    @Nullable
    @Override
    public PageId evict() {
      synchronized (mLRUCache) {
        return mLRUCache.isEmpty() ? null : mLRUCache.keySet().iterator().next();
      }
    }
  
    @Nullable
    @Override
    public PageId evictMatching(Predicate<PageId> criterion) {
      synchronized (mLRUCache) {
        for (PageId candidate : mLRUCache.keySet()) {
          if (criterion.test(candidate)) {
            return candidate;
          }
        }
        return null;
      }
    }
  
    @Override
    public void reset() {
      mLRUCache.clear();
    }
  }
  