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<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Licensed to the Apache Software Foundation (ASF) under one<a name="line.2"></a>
<span class="sourceLineNo">003</span> * or more contributor license agreements. See the NOTICE file<a name="line.3"></a>
<span class="sourceLineNo">004</span> * distributed with this work for additional information<a name="line.4"></a>
<span class="sourceLineNo">005</span> * regarding copyright ownership. The ASF licenses this file<a name="line.5"></a>
<span class="sourceLineNo">006</span> * to you under the Apache License, Version 2.0 (the<a name="line.6"></a>
<span class="sourceLineNo">007</span> * "License"); you may not use this file except in compliance<a name="line.7"></a>
<span class="sourceLineNo">008</span> * with the License. You may obtain a copy of the License at<a name="line.8"></a>
<span class="sourceLineNo">009</span> *<a name="line.9"></a>
<span class="sourceLineNo">010</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.10"></a>
<span class="sourceLineNo">011</span> *<a name="line.11"></a>
<span class="sourceLineNo">012</span> * Unless required by applicable law or agreed to in writing, software<a name="line.12"></a>
<span class="sourceLineNo">013</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.13"></a>
<span class="sourceLineNo">014</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.14"></a>
<span class="sourceLineNo">015</span> * See the License for the specific language governing permissions and<a name="line.15"></a>
<span class="sourceLineNo">016</span> * limitations under the License.<a name="line.16"></a>
<span class="sourceLineNo">017</span> */<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>package org.apache.hadoop.hbase.util;<a name="line.19"></a>
<span class="sourceLineNo">020</span><a name="line.20"></a>
<span class="sourceLineNo">021</span>import java.lang.ref.Reference;<a name="line.21"></a>
<span class="sourceLineNo">022</span>import java.lang.ref.ReferenceQueue;<a name="line.22"></a>
<span class="sourceLineNo">023</span>import java.util.concurrent.ConcurrentHashMap;<a name="line.23"></a>
<span class="sourceLineNo">024</span>import java.util.concurrent.ConcurrentMap;<a name="line.24"></a>
<span class="sourceLineNo">025</span>import java.util.concurrent.locks.Lock;<a name="line.25"></a>
<span class="sourceLineNo">026</span>import java.util.concurrent.locks.ReentrantLock;<a name="line.26"></a>
<span class="sourceLineNo">027</span><a name="line.27"></a>
<span class="sourceLineNo">028</span>import org.apache.yetus.audience.InterfaceAudience;<a name="line.28"></a>
<span class="sourceLineNo">029</span><a name="line.29"></a>
<span class="sourceLineNo">030</span>/**<a name="line.30"></a>
<span class="sourceLineNo">031</span> * A thread-safe shared object pool in which object creation is expected to be lightweight, and the<a name="line.31"></a>
<span class="sourceLineNo">032</span> * objects may be excessively created and discarded.<a name="line.32"></a>
<span class="sourceLineNo">033</span> */<a name="line.33"></a>
<span class="sourceLineNo">034</span>@InterfaceAudience.Private<a name="line.34"></a>
<span class="sourceLineNo">035</span>public abstract class ObjectPool&lt;K, V&gt; {<a name="line.35"></a>
<span class="sourceLineNo">036</span> /**<a name="line.36"></a>
<span class="sourceLineNo">037</span> * An {@code ObjectFactory} object is used to create<a name="line.37"></a>
<span class="sourceLineNo">038</span> * new shared objects on demand.<a name="line.38"></a>
<span class="sourceLineNo">039</span> */<a name="line.39"></a>
<span class="sourceLineNo">040</span> public interface ObjectFactory&lt;K, V&gt; {<a name="line.40"></a>
<span class="sourceLineNo">041</span> /**<a name="line.41"></a>
<span class="sourceLineNo">042</span> * Creates a new shared object associated with the given {@code key},<a name="line.42"></a>
<span class="sourceLineNo">043</span> * identified by the {@code equals} method.<a name="line.43"></a>
<span class="sourceLineNo">044</span> * This method may be simultaneously called by multiple threads<a name="line.44"></a>
<span class="sourceLineNo">045</span> * with the same key, and the excessive objects are just discarded.<a name="line.45"></a>
<span class="sourceLineNo">046</span> */<a name="line.46"></a>
<span class="sourceLineNo">047</span> V createObject(K key);<a name="line.47"></a>
<span class="sourceLineNo">048</span> }<a name="line.48"></a>
<span class="sourceLineNo">049</span><a name="line.49"></a>
<span class="sourceLineNo">050</span> protected final ReferenceQueue&lt;V&gt; staleRefQueue = new ReferenceQueue&lt;&gt;();<a name="line.50"></a>
<span class="sourceLineNo">051</span><a name="line.51"></a>
<span class="sourceLineNo">052</span> private final ObjectFactory&lt;K, V&gt; objectFactory;<a name="line.52"></a>
<span class="sourceLineNo">053</span><a name="line.53"></a>
<span class="sourceLineNo">054</span> /** Does not permit null keys. */<a name="line.54"></a>
<span class="sourceLineNo">055</span> protected final ConcurrentMap&lt;K, Reference&lt;V&gt;&gt; referenceCache;<a name="line.55"></a>
<span class="sourceLineNo">056</span><a name="line.56"></a>
<span class="sourceLineNo">057</span> /** For preventing parallel purge */<a name="line.57"></a>
<span class="sourceLineNo">058</span> private final Lock purgeLock = new ReentrantLock();<a name="line.58"></a>
<span class="sourceLineNo">059</span><a name="line.59"></a>
<span class="sourceLineNo">060</span> /**<a name="line.60"></a>
<span class="sourceLineNo">061</span> * The default initial capacity,<a name="line.61"></a>
<span class="sourceLineNo">062</span> * used when not otherwise specified in a constructor.<a name="line.62"></a>
<span class="sourceLineNo">063</span> */<a name="line.63"></a>
<span class="sourceLineNo">064</span> public static final int DEFAULT_INITIAL_CAPACITY = 16;<a name="line.64"></a>
<span class="sourceLineNo">065</span><a name="line.65"></a>
<span class="sourceLineNo">066</span> /**<a name="line.66"></a>
<span class="sourceLineNo">067</span> * The default concurrency level,<a name="line.67"></a>
<span class="sourceLineNo">068</span> * used when not otherwise specified in a constructor.<a name="line.68"></a>
<span class="sourceLineNo">069</span> */<a name="line.69"></a>
<span class="sourceLineNo">070</span> public static final int DEFAULT_CONCURRENCY_LEVEL = 16;<a name="line.70"></a>
<span class="sourceLineNo">071</span><a name="line.71"></a>
<span class="sourceLineNo">072</span> /**<a name="line.72"></a>
<span class="sourceLineNo">073</span> * Creates a new pool with the default initial capacity (16)<a name="line.73"></a>
<span class="sourceLineNo">074</span> * and the default concurrency level (16).<a name="line.74"></a>
<span class="sourceLineNo">075</span> *<a name="line.75"></a>
<span class="sourceLineNo">076</span> * @param objectFactory the factory to supply new objects on demand<a name="line.76"></a>
<span class="sourceLineNo">077</span> *<a name="line.77"></a>
<span class="sourceLineNo">078</span> * @throws NullPointerException if {@code objectFactory} is null<a name="line.78"></a>
<span class="sourceLineNo">079</span> */<a name="line.79"></a>
<span class="sourceLineNo">080</span> public ObjectPool(ObjectFactory&lt;K, V&gt; objectFactory) {<a name="line.80"></a>
<span class="sourceLineNo">081</span> this(objectFactory, DEFAULT_INITIAL_CAPACITY, DEFAULT_CONCURRENCY_LEVEL);<a name="line.81"></a>
<span class="sourceLineNo">082</span> }<a name="line.82"></a>
<span class="sourceLineNo">083</span><a name="line.83"></a>
<span class="sourceLineNo">084</span> /**<a name="line.84"></a>
<span class="sourceLineNo">085</span> * Creates a new pool with the given initial capacity<a name="line.85"></a>
<span class="sourceLineNo">086</span> * and the default concurrency level (16).<a name="line.86"></a>
<span class="sourceLineNo">087</span> *<a name="line.87"></a>
<span class="sourceLineNo">088</span> * @param objectFactory the factory to supply new objects on demand<a name="line.88"></a>
<span class="sourceLineNo">089</span> * @param initialCapacity the initial capacity to keep objects in the pool<a name="line.89"></a>
<span class="sourceLineNo">090</span> *<a name="line.90"></a>
<span class="sourceLineNo">091</span> * @throws NullPointerException if {@code objectFactory} is null<a name="line.91"></a>
<span class="sourceLineNo">092</span> * @throws IllegalArgumentException if {@code initialCapacity} is negative<a name="line.92"></a>
<span class="sourceLineNo">093</span> */<a name="line.93"></a>
<span class="sourceLineNo">094</span> public ObjectPool(ObjectFactory&lt;K, V&gt; objectFactory, int initialCapacity) {<a name="line.94"></a>
<span class="sourceLineNo">095</span> this(objectFactory, initialCapacity, DEFAULT_CONCURRENCY_LEVEL);<a name="line.95"></a>
<span class="sourceLineNo">096</span> }<a name="line.96"></a>
<span class="sourceLineNo">097</span><a name="line.97"></a>
<span class="sourceLineNo">098</span> /**<a name="line.98"></a>
<span class="sourceLineNo">099</span> * Creates a new pool with the given initial capacity<a name="line.99"></a>
<span class="sourceLineNo">100</span> * and the given concurrency level.<a name="line.100"></a>
<span class="sourceLineNo">101</span> *<a name="line.101"></a>
<span class="sourceLineNo">102</span> * @param objectFactory the factory to supply new objects on demand<a name="line.102"></a>
<span class="sourceLineNo">103</span> * @param initialCapacity the initial capacity to keep objects in the pool<a name="line.103"></a>
<span class="sourceLineNo">104</span> * @param concurrencyLevel the estimated count of concurrently accessing threads<a name="line.104"></a>
<span class="sourceLineNo">105</span> *<a name="line.105"></a>
<span class="sourceLineNo">106</span> * @throws NullPointerException if {@code objectFactory} is null<a name="line.106"></a>
<span class="sourceLineNo">107</span> * @throws IllegalArgumentException if {@code initialCapacity} is negative or<a name="line.107"></a>
<span class="sourceLineNo">108</span> * {@code concurrencyLevel} is non-positive<a name="line.108"></a>
<span class="sourceLineNo">109</span> */<a name="line.109"></a>
<span class="sourceLineNo">110</span> public ObjectPool(<a name="line.110"></a>
<span class="sourceLineNo">111</span> ObjectFactory&lt;K, V&gt; objectFactory,<a name="line.111"></a>
<span class="sourceLineNo">112</span> int initialCapacity,<a name="line.112"></a>
<span class="sourceLineNo">113</span> int concurrencyLevel) {<a name="line.113"></a>
<span class="sourceLineNo">114</span><a name="line.114"></a>
<span class="sourceLineNo">115</span> if (objectFactory == null) {<a name="line.115"></a>
<span class="sourceLineNo">116</span> throw new NullPointerException("Given object factory instance is NULL");<a name="line.116"></a>
<span class="sourceLineNo">117</span> }<a name="line.117"></a>
<span class="sourceLineNo">118</span> this.objectFactory = objectFactory;<a name="line.118"></a>
<span class="sourceLineNo">119</span><a name="line.119"></a>
<span class="sourceLineNo">120</span> this.referenceCache =<a name="line.120"></a>
<span class="sourceLineNo">121</span> new ConcurrentHashMap&lt;K, Reference&lt;V&gt;&gt;(initialCapacity, 0.75f, concurrencyLevel);<a name="line.121"></a>
<span class="sourceLineNo">122</span> }<a name="line.122"></a>
<span class="sourceLineNo">123</span><a name="line.123"></a>
<span class="sourceLineNo">124</span> /**<a name="line.124"></a>
<span class="sourceLineNo">125</span> * Removes stale references of shared objects from the pool. References newly becoming stale may<a name="line.125"></a>
<span class="sourceLineNo">126</span> * still remain.<a name="line.126"></a>
<span class="sourceLineNo">127</span> * &lt;p/&gt;<a name="line.127"></a>
<span class="sourceLineNo">128</span> * The implementation of this method is expected to be lightweight when there is no stale<a name="line.128"></a>
<span class="sourceLineNo">129</span> * reference with the Oracle (Sun) implementation of {@code ReferenceQueue}, because<a name="line.129"></a>
<span class="sourceLineNo">130</span> * {@code ReferenceQueue.poll} just checks a volatile instance variable in {@code ReferenceQueue}.<a name="line.130"></a>
<span class="sourceLineNo">131</span> */<a name="line.131"></a>
<span class="sourceLineNo">132</span> public void purge() {<a name="line.132"></a>
<span class="sourceLineNo">133</span> if (purgeLock.tryLock()) {// no parallel purge<a name="line.133"></a>
<span class="sourceLineNo">134</span> try {<a name="line.134"></a>
<span class="sourceLineNo">135</span> while (true) {<a name="line.135"></a>
<span class="sourceLineNo">136</span> @SuppressWarnings("unchecked")<a name="line.136"></a>
<span class="sourceLineNo">137</span> Reference&lt;V&gt; ref = (Reference&lt;V&gt;) staleRefQueue.poll();<a name="line.137"></a>
<span class="sourceLineNo">138</span> if (ref == null) {<a name="line.138"></a>
<span class="sourceLineNo">139</span> break;<a name="line.139"></a>
<span class="sourceLineNo">140</span> }<a name="line.140"></a>
<span class="sourceLineNo">141</span> referenceCache.remove(getReferenceKey(ref), ref);<a name="line.141"></a>
<span class="sourceLineNo">142</span> }<a name="line.142"></a>
<span class="sourceLineNo">143</span> } finally {<a name="line.143"></a>
<span class="sourceLineNo">144</span> purgeLock.unlock();<a name="line.144"></a>
<span class="sourceLineNo">145</span> }<a name="line.145"></a>
<span class="sourceLineNo">146</span> }<a name="line.146"></a>
<span class="sourceLineNo">147</span> }<a name="line.147"></a>
<span class="sourceLineNo">148</span><a name="line.148"></a>
<span class="sourceLineNo">149</span> /**<a name="line.149"></a>
<span class="sourceLineNo">150</span> * Create a reference associated with the given object<a name="line.150"></a>
<span class="sourceLineNo">151</span> * @param key the key to store in the reference<a name="line.151"></a>
<span class="sourceLineNo">152</span> * @param obj the object to associate with<a name="line.152"></a>
<span class="sourceLineNo">153</span> * @return the reference instance<a name="line.153"></a>
<span class="sourceLineNo">154</span> */<a name="line.154"></a>
<span class="sourceLineNo">155</span> public abstract Reference&lt;V&gt; createReference(K key, V obj);<a name="line.155"></a>
<span class="sourceLineNo">156</span><a name="line.156"></a>
<span class="sourceLineNo">157</span> /**<a name="line.157"></a>
<span class="sourceLineNo">158</span> * Get key of the given reference<a name="line.158"></a>
<span class="sourceLineNo">159</span> * @param ref The reference<a name="line.159"></a>
<span class="sourceLineNo">160</span> * @return key of the reference<a name="line.160"></a>
<span class="sourceLineNo">161</span> */<a name="line.161"></a>
<span class="sourceLineNo">162</span> public abstract K getReferenceKey(Reference&lt;V&gt; ref);<a name="line.162"></a>
<span class="sourceLineNo">163</span><a name="line.163"></a>
<span class="sourceLineNo">164</span> /**<a name="line.164"></a>
<span class="sourceLineNo">165</span> * Returns a shared object associated with the given {@code key},<a name="line.165"></a>
<span class="sourceLineNo">166</span> * which is identified by the {@code equals} method.<a name="line.166"></a>
<span class="sourceLineNo">167</span> * @throws NullPointerException if {@code key} is null<a name="line.167"></a>
<span class="sourceLineNo">168</span> */<a name="line.168"></a>
<span class="sourceLineNo">169</span> public V get(K key) {<a name="line.169"></a>
<span class="sourceLineNo">170</span> Reference&lt;V&gt; ref = referenceCache.get(key);<a name="line.170"></a>
<span class="sourceLineNo">171</span> if (ref != null) {<a name="line.171"></a>
<span class="sourceLineNo">172</span> V obj = ref.get();<a name="line.172"></a>
<span class="sourceLineNo">173</span> if (obj != null) {<a name="line.173"></a>
<span class="sourceLineNo">174</span> return obj;<a name="line.174"></a>
<span class="sourceLineNo">175</span> }<a name="line.175"></a>
<span class="sourceLineNo">176</span> referenceCache.remove(key, ref);<a name="line.176"></a>
<span class="sourceLineNo">177</span> }<a name="line.177"></a>
<span class="sourceLineNo">178</span><a name="line.178"></a>
<span class="sourceLineNo">179</span> V newObj = objectFactory.createObject(key);<a name="line.179"></a>
<span class="sourceLineNo">180</span> Reference&lt;V&gt; newRef = createReference(key, newObj);<a name="line.180"></a>
<span class="sourceLineNo">181</span> while (true) {<a name="line.181"></a>
<span class="sourceLineNo">182</span> Reference&lt;V&gt; existingRef = referenceCache.putIfAbsent(key, newRef);<a name="line.182"></a>
<span class="sourceLineNo">183</span> if (existingRef == null) {<a name="line.183"></a>
<span class="sourceLineNo">184</span> return newObj;<a name="line.184"></a>
<span class="sourceLineNo">185</span> }<a name="line.185"></a>
<span class="sourceLineNo">186</span><a name="line.186"></a>
<span class="sourceLineNo">187</span> V existingObject = existingRef.get();<a name="line.187"></a>
<span class="sourceLineNo">188</span> if (existingObject != null) {<a name="line.188"></a>
<span class="sourceLineNo">189</span> return existingObject;<a name="line.189"></a>
<span class="sourceLineNo">190</span> }<a name="line.190"></a>
<span class="sourceLineNo">191</span> referenceCache.remove(key, existingRef);<a name="line.191"></a>
<span class="sourceLineNo">192</span> }<a name="line.192"></a>
<span class="sourceLineNo">193</span> }<a name="line.193"></a>
<span class="sourceLineNo">194</span><a name="line.194"></a>
<span class="sourceLineNo">195</span> /**<a name="line.195"></a>
<span class="sourceLineNo">196</span> * Returns an estimated count of objects kept in the pool.<a name="line.196"></a>
<span class="sourceLineNo">197</span> * This also counts stale references,<a name="line.197"></a>
<span class="sourceLineNo">198</span> * and you might want to call {@link #purge()} beforehand.<a name="line.198"></a>
<span class="sourceLineNo">199</span> */<a name="line.199"></a>
<span class="sourceLineNo">200</span> public int size() {<a name="line.200"></a>
<span class="sourceLineNo">201</span> return referenceCache.size();<a name="line.201"></a>
<span class="sourceLineNo">202</span> }<a name="line.202"></a>
<span class="sourceLineNo">203</span>}<a name="line.203"></a>
</pre>
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