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.LinkedList;
  import java.util.function.Predicate;
  import javax.annotation.Nullable;
  import javax.annotation.concurrent.NotThreadSafe;
  
  /**
   * Implementation of Evictor using FIFO eviction policy.
   */
  @NotThreadSafe
  public class FIFOCacheEvictor implements CacheEvictor {
    private final LinkedList<PageId> mQueue = new LinkedList<>();
  
    /**
     * Required constructor.
     *
     * @param options
     */
    public FIFOCacheEvictor(CacheEvictorOptions options) {}
  
    @Override
    public void updateOnGet(PageId pageId) {
      // noop
    }
  
    @Override
    public void updateOnPut(PageId pageId) {
      mQueue.add(pageId);
    }
  
    @Override
    public void updateOnDelete(PageId pageId) {
      int idx = mQueue.indexOf(pageId);
      if (idx >= 0) {
        mQueue.remove(idx);
      }
    }
  
    @Override
    public PageId evict() {
      return mQueue.peek();
    }
  
    @Nullable
    @Override
    public PageId evictMatching(Predicate<PageId> criterion) {
      for (PageId candidate : mQueue) {
        if (criterion.test(candidate)) {
          return candidate;
        }
      }
      return null;
    }
  
    @Override
    public void reset() {
      mQueue.clear();
    }
  }
  