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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.util.Arrays;</span>
<span class="source-line-no">021</span><span id="line-21">import java.util.LinkedHashMap;</span>
<span class="source-line-no">022</span><span id="line-22">import java.util.Map;</span>
<span class="source-line-no">023</span><span id="line-23">import java.util.Set;</span>
<span class="source-line-no">024</span><span id="line-24">import java.util.concurrent.locks.Lock;</span>
<span class="source-line-no">025</span><span id="line-25">import java.util.concurrent.locks.ReentrantLock;</span>
<span class="source-line-no">026</span><span id="line-26">import org.apache.yetus.audience.InterfaceAudience;</span>
<span class="source-line-no">027</span><span id="line-27"></span>
<span class="source-line-no">028</span><span id="line-28">/**</span>
<span class="source-line-no">029</span><span id="line-29"> * A utility class to manage a set of locks. Each lock is identified by a String which serves as a</span>
<span class="source-line-no">030</span><span id="line-30"> * key. Typical usage is:</span>
<span class="source-line-no">031</span><span id="line-31"> *</span>
<span class="source-line-no">032</span><span id="line-32"> * &lt;pre&gt;</span>
<span class="source-line-no">033</span><span id="line-33"> * class Example {</span>
<span class="source-line-no">034</span><span id="line-34"> * private final static KeyLocker&amp;lt;String&amp;gt; locker = new Locker&amp;lt;String&amp;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"> * public void foo(String s) {</span>
<span class="source-line-no">037</span><span id="line-37"> * Lock lock = locker.acquireLock(s);</span>
<span class="source-line-no">038</span><span id="line-38"> * try {</span>
<span class="source-line-no">039</span><span id="line-39"> * // whatever</span>
<span class="source-line-no">040</span><span id="line-40"> * } finally {</span>
<span class="source-line-no">041</span><span id="line-41"> * lock.unlock();</span>
<span class="source-line-no">042</span><span id="line-42"> * }</span>
<span class="source-line-no">043</span><span id="line-43"> * }</span>
<span class="source-line-no">044</span><span id="line-44"> * }</span>
<span class="source-line-no">045</span><span id="line-45"> * &lt;/pre&gt;</span>
<span class="source-line-no">046</span><span id="line-46"> */</span>
<span class="source-line-no">047</span><span id="line-47">@InterfaceAudience.Private</span>
<span class="source-line-no">048</span><span id="line-48">public class KeyLocker&lt;K&gt; {</span>
<span class="source-line-no">049</span><span id="line-49"> // The number of lock we want to easily support. It's not a maximum.</span>
<span class="source-line-no">050</span><span id="line-50"> private static final int NB_CONCURRENT_LOCKS = 1000;</span>
<span class="source-line-no">051</span><span id="line-51"></span>
<span class="source-line-no">052</span><span id="line-52"> private final WeakObjectPool&lt;K, ReentrantLock&gt; lockPool =</span>
<span class="source-line-no">053</span><span id="line-53"> new WeakObjectPool&lt;&gt;(new ObjectPool.ObjectFactory&lt;K, ReentrantLock&gt;() {</span>
<span class="source-line-no">054</span><span id="line-54"> @Override</span>
<span class="source-line-no">055</span><span id="line-55"> public ReentrantLock createObject(K key) {</span>
<span class="source-line-no">056</span><span id="line-56"> return new ReentrantLock();</span>
<span class="source-line-no">057</span><span id="line-57"> }</span>
<span class="source-line-no">058</span><span id="line-58"> }, NB_CONCURRENT_LOCKS);</span>
<span class="source-line-no">059</span><span id="line-59"></span>
<span class="source-line-no">060</span><span id="line-60"> /**</span>
<span class="source-line-no">061</span><span id="line-61"> * Return a lock for the given key. The lock is already locked.</span>
<span class="source-line-no">062</span><span id="line-62"> */</span>
<span class="source-line-no">063</span><span id="line-63"> public ReentrantLock acquireLock(K key) {</span>
<span class="source-line-no">064</span><span id="line-64"> if (key == null) throw new IllegalArgumentException("key must not be null");</span>
<span class="source-line-no">065</span><span id="line-65"></span>
<span class="source-line-no">066</span><span id="line-66"> lockPool.purge();</span>
<span class="source-line-no">067</span><span id="line-67"> ReentrantLock lock = lockPool.get(key);</span>
<span class="source-line-no">068</span><span id="line-68"></span>
<span class="source-line-no">069</span><span id="line-69"> lock.lock();</span>
<span class="source-line-no">070</span><span id="line-70"> return lock;</span>
<span class="source-line-no">071</span><span id="line-71"> }</span>
<span class="source-line-no">072</span><span id="line-72"></span>
<span class="source-line-no">073</span><span id="line-73"> /**</span>
<span class="source-line-no">074</span><span id="line-74"> * Acquire locks for a set of keys. The keys will be sorted internally to avoid possible deadlock.</span>
<span class="source-line-no">075</span><span id="line-75"> * @throws ClassCastException if the given {@code keys} contains elements that are not mutually</span>
<span class="source-line-no">076</span><span id="line-76"> * comparable</span>
<span class="source-line-no">077</span><span id="line-77"> */</span>
<span class="source-line-no">078</span><span id="line-78"> public Map&lt;K, Lock&gt; acquireLocks(Set&lt;? extends K&gt; keys) {</span>
<span class="source-line-no">079</span><span id="line-79"> Object[] keyArray = keys.toArray();</span>
<span class="source-line-no">080</span><span id="line-80"> Arrays.sort(keyArray);</span>
<span class="source-line-no">081</span><span id="line-81"></span>
<span class="source-line-no">082</span><span id="line-82"> lockPool.purge();</span>
<span class="source-line-no">083</span><span id="line-83"> Map&lt;K, Lock&gt; locks = new LinkedHashMap&lt;&gt;(keyArray.length);</span>
<span class="source-line-no">084</span><span id="line-84"> for (Object o : keyArray) {</span>
<span class="source-line-no">085</span><span id="line-85"> @SuppressWarnings("unchecked")</span>
<span class="source-line-no">086</span><span id="line-86"> K key = (K) o;</span>
<span class="source-line-no">087</span><span id="line-87"> ReentrantLock lock = lockPool.get(key);</span>
<span class="source-line-no">088</span><span id="line-88"> locks.put(key, lock);</span>
<span class="source-line-no">089</span><span id="line-89"> }</span>
<span class="source-line-no">090</span><span id="line-90"></span>
<span class="source-line-no">091</span><span id="line-91"> for (Lock lock : locks.values()) {</span>
<span class="source-line-no">092</span><span id="line-92"> lock.lock();</span>
<span class="source-line-no">093</span><span id="line-93"> }</span>
<span class="source-line-no">094</span><span id="line-94"> return locks;</span>
<span class="source-line-no">095</span><span id="line-95"> }</span>
<span class="source-line-no">096</span><span id="line-96">}</span>
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