001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.util;
019
020import java.lang.ref.Reference;
021import java.lang.ref.SoftReference;
022import org.apache.yetus.audience.InterfaceAudience;
023
024/**
025 * A {@code SoftReference} based shared object pool. The objects are kept in soft references and
026 * associated with keys which are identified by the {@code equals} method. The objects are created
027 * by ObjectFactory on demand. The object creation is expected to be lightweight, and the objects
028 * may be excessively created and discarded. Thread safe.
029 */
030@InterfaceAudience.Private
031public class SoftObjectPool<K, V> extends ObjectPool<K, V> {
032
033  public SoftObjectPool(ObjectFactory<K, V> objectFactory) {
034    super(objectFactory);
035  }
036
037  public SoftObjectPool(ObjectFactory<K, V> objectFactory, int initialCapacity) {
038    super(objectFactory, initialCapacity);
039  }
040
041  public SoftObjectPool(ObjectFactory<K, V> objectFactory, int initialCapacity,
042    int concurrencyLevel) {
043    super(objectFactory, initialCapacity, concurrencyLevel);
044  }
045
046  @Override
047  public Reference<V> createReference(K key, V obj) {
048    return new SoftObjectReference(key, obj);
049  }
050
051  private class SoftObjectReference extends SoftReference<V> {
052    final K key;
053
054    SoftObjectReference(K key, V obj) {
055      super(obj, staleRefQueue);
056      this.key = key;
057    }
058  }
059
060  @Override
061  public K getReferenceKey(Reference<V> ref) {
062    return ((SoftObjectReference) ref).key;
063  }
064
065}