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<pre><span class="source-line-no">001</span><span id="line-1">/*</span>
<span class="source-line-no">002</span><span id="line-2"> * Licensed to the Apache Software Foundation (ASF) under one</span>
<span class="source-line-no">003</span><span id="line-3"> * or more contributor license agreements. See the NOTICE file</span>
<span class="source-line-no">004</span><span id="line-4"> * distributed with this work for additional information</span>
<span class="source-line-no">005</span><span id="line-5"> * regarding copyright ownership. The ASF licenses this file</span>
<span class="source-line-no">006</span><span id="line-6"> * to you under the Apache License, Version 2.0 (the</span>
<span class="source-line-no">007</span><span id="line-7"> * "License"); you may not use this file except in compliance</span>
<span class="source-line-no">008</span><span id="line-8"> * with the License. You may obtain a copy of the License at</span>
<span class="source-line-no">009</span><span id="line-9"> *</span>
<span class="source-line-no">010</span><span id="line-10"> * http://www.apache.org/licenses/LICENSE-2.0</span>
<span class="source-line-no">011</span><span id="line-11"> *</span>
<span class="source-line-no">012</span><span id="line-12"> * Unless required by applicable law or agreed to in writing, software</span>
<span class="source-line-no">013</span><span id="line-13"> * distributed under the License is distributed on an "AS IS" BASIS,</span>
<span class="source-line-no">014</span><span id="line-14"> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.</span>
<span class="source-line-no">015</span><span id="line-15"> * See the License for the specific language governing permissions and</span>
<span class="source-line-no">016</span><span id="line-16"> * limitations under the License.</span>
<span class="source-line-no">017</span><span id="line-17"> */</span>
<span class="source-line-no">018</span><span id="line-18">package org.apache.hadoop.hbase.util;</span>
<span class="source-line-no">019</span><span id="line-19"></span>
<span class="source-line-no">020</span><span id="line-20">import java.lang.ref.Reference;</span>
<span class="source-line-no">021</span><span id="line-21">import java.lang.ref.ReferenceQueue;</span>
<span class="source-line-no">022</span><span id="line-22">import java.util.Objects;</span>
<span class="source-line-no">023</span><span id="line-23">import java.util.concurrent.ConcurrentHashMap;</span>
<span class="source-line-no">024</span><span id="line-24">import java.util.concurrent.ConcurrentMap;</span>
<span class="source-line-no">025</span><span id="line-25">import java.util.concurrent.locks.Lock;</span>
<span class="source-line-no">026</span><span id="line-26">import java.util.concurrent.locks.ReentrantLock;</span>
<span class="source-line-no">027</span><span id="line-27">import org.apache.yetus.audience.InterfaceAudience;</span>
<span class="source-line-no">028</span><span id="line-28"></span>
<span class="source-line-no">029</span><span id="line-29">/**</span>
<span class="source-line-no">030</span><span id="line-30"> * A thread-safe shared object pool in which object creation is expected to be lightweight, and the</span>
<span class="source-line-no">031</span><span id="line-31"> * objects may be excessively created and discarded.</span>
<span class="source-line-no">032</span><span id="line-32"> */</span>
<span class="source-line-no">033</span><span id="line-33">@InterfaceAudience.Private</span>
<span class="source-line-no">034</span><span id="line-34">public abstract class ObjectPool&lt;K, V&gt; {</span>
<span class="source-line-no">035</span><span id="line-35"> /**</span>
<span class="source-line-no">036</span><span id="line-36"> * An {@code ObjectFactory} object is used to create new shared objects on demand.</span>
<span class="source-line-no">037</span><span id="line-37"> */</span>
<span class="source-line-no">038</span><span id="line-38"> public interface ObjectFactory&lt;K, V&gt; {</span>
<span class="source-line-no">039</span><span id="line-39"> /**</span>
<span class="source-line-no">040</span><span id="line-40"> * Creates a new shared object associated with the given {@code key}, identified by the</span>
<span class="source-line-no">041</span><span id="line-41"> * {@code equals} method. This method may be simultaneously called by multiple threads with the</span>
<span class="source-line-no">042</span><span id="line-42"> * same key, and the excessive objects are just discarded.</span>
<span class="source-line-no">043</span><span id="line-43"> */</span>
<span class="source-line-no">044</span><span id="line-44"> V createObject(K key);</span>
<span class="source-line-no">045</span><span id="line-45"> }</span>
<span class="source-line-no">046</span><span id="line-46"></span>
<span class="source-line-no">047</span><span id="line-47"> protected final ReferenceQueue&lt;V&gt; staleRefQueue = new ReferenceQueue&lt;&gt;();</span>
<span class="source-line-no">048</span><span id="line-48"></span>
<span class="source-line-no">049</span><span id="line-49"> private final ObjectFactory&lt;K, V&gt; objectFactory;</span>
<span class="source-line-no">050</span><span id="line-50"></span>
<span class="source-line-no">051</span><span id="line-51"> /** Does not permit null keys. */</span>
<span class="source-line-no">052</span><span id="line-52"> protected final ConcurrentMap&lt;K, Reference&lt;V&gt;&gt; referenceCache;</span>
<span class="source-line-no">053</span><span id="line-53"></span>
<span class="source-line-no">054</span><span id="line-54"> /** For preventing parallel purge */</span>
<span class="source-line-no">055</span><span id="line-55"> private final Lock purgeLock = new ReentrantLock();</span>
<span class="source-line-no">056</span><span id="line-56"></span>
<span class="source-line-no">057</span><span id="line-57"> /**</span>
<span class="source-line-no">058</span><span id="line-58"> * The default initial capacity, used when not otherwise specified in a constructor.</span>
<span class="source-line-no">059</span><span id="line-59"> */</span>
<span class="source-line-no">060</span><span id="line-60"> public static final int DEFAULT_INITIAL_CAPACITY = 16;</span>
<span class="source-line-no">061</span><span id="line-61"></span>
<span class="source-line-no">062</span><span id="line-62"> /**</span>
<span class="source-line-no">063</span><span id="line-63"> * The default concurrency level, used when not otherwise specified in a constructor.</span>
<span class="source-line-no">064</span><span id="line-64"> */</span>
<span class="source-line-no">065</span><span id="line-65"> public static final int DEFAULT_CONCURRENCY_LEVEL = 16;</span>
<span class="source-line-no">066</span><span id="line-66"></span>
<span class="source-line-no">067</span><span id="line-67"> /**</span>
<span class="source-line-no">068</span><span id="line-68"> * Creates a new pool with the default initial capacity (16) and the default concurrency level</span>
<span class="source-line-no">069</span><span id="line-69"> * (16).</span>
<span class="source-line-no">070</span><span id="line-70"> * @param objectFactory the factory to supply new objects on demand</span>
<span class="source-line-no">071</span><span id="line-71"> * @throws NullPointerException if {@code objectFactory} is {@code null}</span>
<span class="source-line-no">072</span><span id="line-72"> */</span>
<span class="source-line-no">073</span><span id="line-73"> public ObjectPool(ObjectFactory&lt;K, V&gt; objectFactory) {</span>
<span class="source-line-no">074</span><span id="line-74"> this(objectFactory, DEFAULT_INITIAL_CAPACITY, DEFAULT_CONCURRENCY_LEVEL);</span>
<span class="source-line-no">075</span><span id="line-75"> }</span>
<span class="source-line-no">076</span><span id="line-76"></span>
<span class="source-line-no">077</span><span id="line-77"> /**</span>
<span class="source-line-no">078</span><span id="line-78"> * Creates a new pool with the given initial capacity and the default concurrency level (16).</span>
<span class="source-line-no">079</span><span id="line-79"> * @param objectFactory the factory to supply new objects on demand</span>
<span class="source-line-no">080</span><span id="line-80"> * @param initialCapacity the initial capacity to keep objects in the pool</span>
<span class="source-line-no">081</span><span id="line-81"> * @throws NullPointerException if {@code objectFactory} is {@code null}</span>
<span class="source-line-no">082</span><span id="line-82"> * @throws IllegalArgumentException if {@code initialCapacity} is negative</span>
<span class="source-line-no">083</span><span id="line-83"> */</span>
<span class="source-line-no">084</span><span id="line-84"> public ObjectPool(ObjectFactory&lt;K, V&gt; objectFactory, int initialCapacity) {</span>
<span class="source-line-no">085</span><span id="line-85"> this(objectFactory, initialCapacity, DEFAULT_CONCURRENCY_LEVEL);</span>
<span class="source-line-no">086</span><span id="line-86"> }</span>
<span class="source-line-no">087</span><span id="line-87"></span>
<span class="source-line-no">088</span><span id="line-88"> /**</span>
<span class="source-line-no">089</span><span id="line-89"> * Creates a new pool with the given initial capacity and the given concurrency level.</span>
<span class="source-line-no">090</span><span id="line-90"> * @param objectFactory the factory to supply new objects on demand</span>
<span class="source-line-no">091</span><span id="line-91"> * @param initialCapacity the initial capacity to keep objects in the pool</span>
<span class="source-line-no">092</span><span id="line-92"> * @param concurrencyLevel the estimated count of concurrently accessing threads</span>
<span class="source-line-no">093</span><span id="line-93"> * @throws NullPointerException if {@code objectFactory} is {@code null}</span>
<span class="source-line-no">094</span><span id="line-94"> * @throws IllegalArgumentException if {@code initialCapacity} is negative or</span>
<span class="source-line-no">095</span><span id="line-95"> * {@code concurrencyLevel} is non-positive</span>
<span class="source-line-no">096</span><span id="line-96"> */</span>
<span class="source-line-no">097</span><span id="line-97"> public ObjectPool(ObjectFactory&lt;K, V&gt; objectFactory, int initialCapacity, int concurrencyLevel) {</span>
<span class="source-line-no">098</span><span id="line-98"></span>
<span class="source-line-no">099</span><span id="line-99"> this.objectFactory = Objects.requireNonNull(objectFactory, "Object factory cannot be null");</span>
<span class="source-line-no">100</span><span id="line-100"></span>
<span class="source-line-no">101</span><span id="line-101"> this.referenceCache =</span>
<span class="source-line-no">102</span><span id="line-102"> new ConcurrentHashMap&lt;K, Reference&lt;V&gt;&gt;(initialCapacity, 0.75f, concurrencyLevel);</span>
<span class="source-line-no">103</span><span id="line-103"> }</span>
<span class="source-line-no">104</span><span id="line-104"></span>
<span class="source-line-no">105</span><span id="line-105"> /**</span>
<span class="source-line-no">106</span><span id="line-106"> * Removes stale references of shared objects from the pool. References newly becoming stale may</span>
<span class="source-line-no">107</span><span id="line-107"> * still remain.</span>
<span class="source-line-no">108</span><span id="line-108"> * &lt;p/&gt;</span>
<span class="source-line-no">109</span><span id="line-109"> * The implementation of this method is expected to be lightweight when there is no stale</span>
<span class="source-line-no">110</span><span id="line-110"> * reference with the Oracle (Sun) implementation of {@code ReferenceQueue}, because</span>
<span class="source-line-no">111</span><span id="line-111"> * {@code ReferenceQueue.poll} just checks a volatile instance variable in {@code ReferenceQueue}.</span>
<span class="source-line-no">112</span><span id="line-112"> */</span>
<span class="source-line-no">113</span><span id="line-113"> public void purge() {</span>
<span class="source-line-no">114</span><span id="line-114"> if (purgeLock.tryLock()) {// no parallel purge</span>
<span class="source-line-no">115</span><span id="line-115"> try {</span>
<span class="source-line-no">116</span><span id="line-116"> while (true) {</span>
<span class="source-line-no">117</span><span id="line-117"> @SuppressWarnings("unchecked")</span>
<span class="source-line-no">118</span><span id="line-118"> Reference&lt;V&gt; ref = (Reference&lt;V&gt;) staleRefQueue.poll();</span>
<span class="source-line-no">119</span><span id="line-119"> if (ref == null) {</span>
<span class="source-line-no">120</span><span id="line-120"> break;</span>
<span class="source-line-no">121</span><span id="line-121"> }</span>
<span class="source-line-no">122</span><span id="line-122"> referenceCache.remove(getReferenceKey(ref), ref);</span>
<span class="source-line-no">123</span><span id="line-123"> }</span>
<span class="source-line-no">124</span><span id="line-124"> } finally {</span>
<span class="source-line-no">125</span><span id="line-125"> purgeLock.unlock();</span>
<span class="source-line-no">126</span><span id="line-126"> }</span>
<span class="source-line-no">127</span><span id="line-127"> }</span>
<span class="source-line-no">128</span><span id="line-128"> }</span>
<span class="source-line-no">129</span><span id="line-129"></span>
<span class="source-line-no">130</span><span id="line-130"> /**</span>
<span class="source-line-no">131</span><span id="line-131"> * Create a reference associated with the given object</span>
<span class="source-line-no">132</span><span id="line-132"> * @param key the key to store in the reference</span>
<span class="source-line-no">133</span><span id="line-133"> * @param obj the object to associate with</span>
<span class="source-line-no">134</span><span id="line-134"> * @return the reference instance</span>
<span class="source-line-no">135</span><span id="line-135"> */</span>
<span class="source-line-no">136</span><span id="line-136"> public abstract Reference&lt;V&gt; createReference(K key, V obj);</span>
<span class="source-line-no">137</span><span id="line-137"></span>
<span class="source-line-no">138</span><span id="line-138"> /**</span>
<span class="source-line-no">139</span><span id="line-139"> * Get key of the given reference</span>
<span class="source-line-no">140</span><span id="line-140"> * @param ref The reference</span>
<span class="source-line-no">141</span><span id="line-141"> * @return key of the reference</span>
<span class="source-line-no">142</span><span id="line-142"> */</span>
<span class="source-line-no">143</span><span id="line-143"> public abstract K getReferenceKey(Reference&lt;V&gt; ref);</span>
<span class="source-line-no">144</span><span id="line-144"></span>
<span class="source-line-no">145</span><span id="line-145"> /**</span>
<span class="source-line-no">146</span><span id="line-146"> * Returns a shared object associated with the given {@code key}, which is identified by the</span>
<span class="source-line-no">147</span><span id="line-147"> * {@code equals} method.</span>
<span class="source-line-no">148</span><span id="line-148"> * @throws NullPointerException if {@code key} is {@code null}</span>
<span class="source-line-no">149</span><span id="line-149"> */</span>
<span class="source-line-no">150</span><span id="line-150"> public V get(K key) {</span>
<span class="source-line-no">151</span><span id="line-151"> Reference&lt;V&gt; ref = referenceCache.get(Objects.requireNonNull(key));</span>
<span class="source-line-no">152</span><span id="line-152"> if (ref != null) {</span>
<span class="source-line-no">153</span><span id="line-153"> V obj = ref.get();</span>
<span class="source-line-no">154</span><span id="line-154"> if (obj != null) {</span>
<span class="source-line-no">155</span><span id="line-155"> return obj;</span>
<span class="source-line-no">156</span><span id="line-156"> }</span>
<span class="source-line-no">157</span><span id="line-157"> referenceCache.remove(key, ref);</span>
<span class="source-line-no">158</span><span id="line-158"> }</span>
<span class="source-line-no">159</span><span id="line-159"></span>
<span class="source-line-no">160</span><span id="line-160"> V newObj = objectFactory.createObject(key);</span>
<span class="source-line-no">161</span><span id="line-161"> Reference&lt;V&gt; newRef = createReference(key, newObj);</span>
<span class="source-line-no">162</span><span id="line-162"> while (true) {</span>
<span class="source-line-no">163</span><span id="line-163"> Reference&lt;V&gt; existingRef = referenceCache.putIfAbsent(key, newRef);</span>
<span class="source-line-no">164</span><span id="line-164"> if (existingRef == null) {</span>
<span class="source-line-no">165</span><span id="line-165"> return newObj;</span>
<span class="source-line-no">166</span><span id="line-166"> }</span>
<span class="source-line-no">167</span><span id="line-167"></span>
<span class="source-line-no">168</span><span id="line-168"> V existingObject = existingRef.get();</span>
<span class="source-line-no">169</span><span id="line-169"> if (existingObject != null) {</span>
<span class="source-line-no">170</span><span id="line-170"> return existingObject;</span>
<span class="source-line-no">171</span><span id="line-171"> }</span>
<span class="source-line-no">172</span><span id="line-172"> referenceCache.remove(key, existingRef);</span>
<span class="source-line-no">173</span><span id="line-173"> }</span>
<span class="source-line-no">174</span><span id="line-174"> }</span>
<span class="source-line-no">175</span><span id="line-175"></span>
<span class="source-line-no">176</span><span id="line-176"> /**</span>
<span class="source-line-no">177</span><span id="line-177"> * Returns an estimated count of objects kept in the pool. This also counts stale references, and</span>
<span class="source-line-no">178</span><span id="line-178"> * you might want to call {@link #purge()} beforehand.</span>
<span class="source-line-no">179</span><span id="line-179"> */</span>
<span class="source-line-no">180</span><span id="line-180"> public int size() {</span>
<span class="source-line-no">181</span><span id="line-181"> return referenceCache.size();</span>
<span class="source-line-no">182</span><span id="line-182"> }</span>
<span class="source-line-no">183</span><span id="line-183">}</span>
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