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}