hbase-common/src/main/java/org/apache/hadoop/hbase/util/SoftObjectPool.java

   1 /**
   2  * Licensed to the Apache Software Foundation (ASF) under one
   3  * or more contributor license agreements.  See the NOTICE file
   4  * distributed with this work for additional information
   5  * regarding copyright ownership.  The ASF licenses this file
   6  * to you under the Apache License, Version 2.0 (the
   7  * "License"); you may not use this file except in compliance
   8  * with the License.  You may obtain a copy of the License at
   9  *
  10  *     http://www.apache.org/licenses/LICENSE-2.0
  11  *
  12  * Unless required by applicable law or agreed to in writing, software
  13  * distributed under the License is distributed on an "AS IS" BASIS,
  14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15  * See the License for the specific language governing permissions and
  16  * limitations under the License.
  17  */
  18 package org.apache.hadoop.hbase.util;
  19
  20 import java.lang.ref.Reference;
  21 import java.lang.ref.SoftReference;
  22
  23 import org.apache.yetus.audience.InterfaceAudience;
  24
  25 /**
  26  * A {@code SoftReference} based shared object pool.
  27  * The objects are kept in soft references and
  28  * associated with keys which are identified by the {@code equals} method.
  29  * The objects are created by ObjectFactory on demand.
  30  * The object creation is expected to be lightweight,
  31  * and the objects may be excessively created and discarded.
  32  * Thread safe.
  33  */
  34 @InterfaceAudience.Private
  35 public class SoftObjectPool<K, V> extends ObjectPool<K, V> {
  36
  37   public SoftObjectPool(ObjectFactory<K, V> objectFactory) {
  38     super(objectFactory);
  39   }
  40
  41   public SoftObjectPool(ObjectFactory<K, V> objectFactory, int initialCapacity) {
  42     super(objectFactory, initialCapacity);
  43   }
  44
  45   public SoftObjectPool(ObjectFactory<K, V> objectFactory, int initialCapacity,
  46       int concurrencyLevel) {
  47     super(objectFactory, initialCapacity, concurrencyLevel);
  48   }
  49
  50   @Override
  51   public Reference<V> createReference(K key, V obj) {
  52     return new SoftObjectReference(key, obj);
  53   }
  54
  55   private class SoftObjectReference extends SoftReference<V> {
  56     final K key;
  57
  58     SoftObjectReference(K key, V obj) {
  59       super(obj, staleRefQueue);
  60       this.key = key;
  61     }
  62   }
  63
  64   @Override
  65   public K getReferenceKey(Reference<V> ref) {
  66     return ((SoftObjectReference) ref).key;
  67   }
  68
  69 }