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;
022
023import org.apache.yetus.audience.InterfaceAudience;
024
025/**
026 * A {@code WeakReference} based shared object pool.
027 * The objects are kept in weak references and
028 * associated with keys which are identified by the {@code equals} method.
029 * The objects are created by {@link org.apache.hadoop.hbase.util.ObjectPool.ObjectFactory} on
030 * demand. The object creation is expected to be lightweight, and the objects may be excessively
031 * created and discarded.
032 * Thread safe.
033 */
034@InterfaceAudience.Private
035public class WeakObjectPool<K,V> extends ObjectPool<K,V> {
036
037  public WeakObjectPool(ObjectFactory<K, V> objectFactory) {
038    super(objectFactory);
039  }
040
041  public WeakObjectPool(ObjectFactory<K, V> objectFactory, int initialCapacity) {
042    super(objectFactory, initialCapacity);
043  }
044
045  public WeakObjectPool(ObjectFactory<K, V> objectFactory, int initialCapacity,
046      int concurrencyLevel) {
047    super(objectFactory, initialCapacity, concurrencyLevel);
048  }
049
050  @Override
051  public Reference<V> createReference(K key, V obj) {
052    return new WeakObjectReference(key, obj);
053  }
054
055  private class WeakObjectReference extends WeakReference<V> {
056    final K key;
057
058    WeakObjectReference(K key, V obj) {
059      super(obj, staleRefQueue);
060      this.key = key;
061    }
062  }
063
064  @Override
065  public K getReferenceKey(Reference<V> ref) {
066    return ((WeakObjectReference)ref).key;
067  }
068
069}