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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.io.IOException;</span>
<span class="source-line-no">021</span><span id="line-21">import java.util.concurrent.ConcurrentMap;</span>
<span class="source-line-no">022</span><span id="line-22">import java.util.function.Supplier;</span>
<span class="source-line-no">023</span><span id="line-23">import org.apache.yetus.audience.InterfaceAudience;</span>
<span class="source-line-no">024</span><span id="line-24"></span>
<span class="source-line-no">025</span><span id="line-25">/**</span>
<span class="source-line-no">026</span><span id="line-26"> * Utility methods for dealing with Collections, including treating null collections as empty.</span>
<span class="source-line-no">027</span><span id="line-27"> */</span>
<span class="source-line-no">028</span><span id="line-28">@InterfaceAudience.Private</span>
<span class="source-line-no">029</span><span id="line-29">public class ConcurrentMapUtils {</span>
<span class="source-line-no">030</span><span id="line-30"></span>
<span class="source-line-no">031</span><span id="line-31"> /**</span>
<span class="source-line-no">032</span><span id="line-32"> * In HBASE-16648 we found that ConcurrentHashMap.get is much faster than computeIfAbsent if the</span>
<span class="source-line-no">033</span><span id="line-33"> * value already exists. Notice that the implementation does not guarantee that the supplier will</span>
<span class="source-line-no">034</span><span id="line-34"> * only be executed once.</span>
<span class="source-line-no">035</span><span id="line-35"> */</span>
<span class="source-line-no">036</span><span id="line-36"> public static &lt;K, V&gt; V computeIfAbsent(ConcurrentMap&lt;K, V&gt; map, K key, Supplier&lt;V&gt; supplier) {</span>
<span class="source-line-no">037</span><span id="line-37"> return computeIfAbsent(map, key, supplier, () -&gt; {</span>
<span class="source-line-no">038</span><span id="line-38"> });</span>
<span class="source-line-no">039</span><span id="line-39"> }</span>
<span class="source-line-no">040</span><span id="line-40"></span>
<span class="source-line-no">041</span><span id="line-41"> /**</span>
<span class="source-line-no">042</span><span id="line-42"> * In HBASE-16648 we found that ConcurrentHashMap.get is much faster than computeIfAbsent if the</span>
<span class="source-line-no">043</span><span id="line-43"> * value already exists. So here we copy the implementation of</span>
<span class="source-line-no">044</span><span id="line-44"> * {@link ConcurrentMap#computeIfAbsent(Object, java.util.function.Function)}. It uses get and</span>
<span class="source-line-no">045</span><span id="line-45"> * putIfAbsent to implement computeIfAbsent. And notice that the implementation does not guarantee</span>
<span class="source-line-no">046</span><span id="line-46"> * that the supplier will only be executed once.</span>
<span class="source-line-no">047</span><span id="line-47"> */</span>
<span class="source-line-no">048</span><span id="line-48"> public static &lt;K, V&gt; V computeIfAbsentEx(ConcurrentMap&lt;K, V&gt; map, K key,</span>
<span class="source-line-no">049</span><span id="line-49"> IOExceptionSupplier&lt;V&gt; supplier) throws IOException {</span>
<span class="source-line-no">050</span><span id="line-50"> V v, newValue;</span>
<span class="source-line-no">051</span><span id="line-51"> return ((v = map.get(key)) == null &amp;&amp; (newValue = supplier.get()) != null</span>
<span class="source-line-no">052</span><span id="line-52"> &amp;&amp; (v = map.putIfAbsent(key, newValue)) == null) ? newValue : v;</span>
<span class="source-line-no">053</span><span id="line-53"> }</span>
<span class="source-line-no">054</span><span id="line-54"></span>
<span class="source-line-no">055</span><span id="line-55"> public static &lt;K, V&gt; V computeIfAbsent(ConcurrentMap&lt;K, V&gt; map, K key, Supplier&lt;V&gt; supplier,</span>
<span class="source-line-no">056</span><span id="line-56"> Runnable actionIfAbsent) {</span>
<span class="source-line-no">057</span><span id="line-57"> V v = map.get(key);</span>
<span class="source-line-no">058</span><span id="line-58"> if (v != null) {</span>
<span class="source-line-no">059</span><span id="line-59"> return v;</span>
<span class="source-line-no">060</span><span id="line-60"> }</span>
<span class="source-line-no">061</span><span id="line-61"> V newValue = supplier.get();</span>
<span class="source-line-no">062</span><span id="line-62"> v = map.putIfAbsent(key, newValue);</span>
<span class="source-line-no">063</span><span id="line-63"> if (v != null) {</span>
<span class="source-line-no">064</span><span id="line-64"> return v;</span>
<span class="source-line-no">065</span><span id="line-65"> }</span>
<span class="source-line-no">066</span><span id="line-66"> actionIfAbsent.run();</span>
<span class="source-line-no">067</span><span id="line-67"> return newValue;</span>
<span class="source-line-no">068</span><span id="line-68"> }</span>
<span class="source-line-no">069</span><span id="line-69">}</span>
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