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.WeakReference;
022import org.apache.yetus.audience.InterfaceAudience;
023
024/**
025 * A {@code WeakReference} based shared object pool. The objects are kept in weak references and
026 * associated with keys which are identified by the {@code equals} method. The objects are created
027 * by {@link org.apache.hadoop.hbase.util.ObjectPool.ObjectFactory} on demand. The object creation
028 * is expected to be lightweight, and the objects may be excessively created and discarded. Thread
029 * safe.
030 */
031@InterfaceAudience.Private
032public class WeakObjectPool<K, V> extends ObjectPool<K, V> {
033
034  public WeakObjectPool(ObjectFactory<K, V> objectFactory) {
035    super(objectFactory);
036  }
037
038  public WeakObjectPool(ObjectFactory<K, V> objectFactory, int initialCapacity) {
039    super(objectFactory, initialCapacity);
040  }
041
042  public WeakObjectPool(ObjectFactory<K, V> objectFactory, int initialCapacity,
043    int concurrencyLevel) {
044    super(objectFactory, initialCapacity, concurrencyLevel);
045  }
046
047  @Override
048  public Reference<V> createReference(K key, V obj) {
049    return new WeakObjectReference(key, obj);
050  }
051
052  private class WeakObjectReference extends WeakReference<V> {
053    final K key;
054
055    WeakObjectReference(K key, V obj) {
056      super(obj, staleRefQueue);
057      this.key = key;
058    }
059  }
060
061  @Override
062  public K getReferenceKey(Reference<V> ref) {
063    return ((WeakObjectReference) ref).key;
064  }
065
066}