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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>package org.apache.hadoop.hbase.zookeeper;<a name="line.18"></a> |
| <span class="sourceLineNo">019</span><a name="line.19"></a> |
| <span class="sourceLineNo">020</span>import java.util.concurrent.CountDownLatch;<a name="line.20"></a> |
| <span class="sourceLineNo">021</span><a name="line.21"></a> |
| <span class="sourceLineNo">022</span>/**<a name="line.22"></a> |
| <span class="sourceLineNo">023</span> * Placeholder of an instance which will be accessed by other threads but is not yet created. Thread<a name="line.23"></a> |
| <span class="sourceLineNo">024</span> * safe.<a name="line.24"></a> |
| <span class="sourceLineNo">025</span> */<a name="line.25"></a> |
| <span class="sourceLineNo">026</span>class InstancePending<T> {<a name="line.26"></a> |
| <span class="sourceLineNo">027</span> // Based on a subtle part of the Java Language Specification,<a name="line.27"></a> |
| <span class="sourceLineNo">028</span> // in order to avoid a slight overhead of synchronization for each access.<a name="line.28"></a> |
| <span class="sourceLineNo">029</span><a name="line.29"></a> |
| <span class="sourceLineNo">030</span> private final CountDownLatch pendingLatch = new CountDownLatch(1);<a name="line.30"></a> |
| <span class="sourceLineNo">031</span><a name="line.31"></a> |
| <span class="sourceLineNo">032</span> /** Piggybacking on {@code pendingLatch}. */<a name="line.32"></a> |
| <span class="sourceLineNo">033</span> private InstanceHolder<T> instanceHolder;<a name="line.33"></a> |
| <span class="sourceLineNo">034</span><a name="line.34"></a> |
| <span class="sourceLineNo">035</span> private static class InstanceHolder<T> {<a name="line.35"></a> |
| <span class="sourceLineNo">036</span> // The JLS ensures the visibility of a final field and its contents<a name="line.36"></a> |
| <span class="sourceLineNo">037</span> // unless they are exposed to another thread while the construction.<a name="line.37"></a> |
| <span class="sourceLineNo">038</span> final T instance;<a name="line.38"></a> |
| <span class="sourceLineNo">039</span><a name="line.39"></a> |
| <span class="sourceLineNo">040</span> InstanceHolder(T instance) {<a name="line.40"></a> |
| <span class="sourceLineNo">041</span> this.instance = instance;<a name="line.41"></a> |
| <span class="sourceLineNo">042</span> }<a name="line.42"></a> |
| <span class="sourceLineNo">043</span> }<a name="line.43"></a> |
| <span class="sourceLineNo">044</span><a name="line.44"></a> |
| <span class="sourceLineNo">045</span> /**<a name="line.45"></a> |
| <span class="sourceLineNo">046</span> * Returns the instance given by the method {@link #prepare}. This is an uninterruptible blocking<a name="line.46"></a> |
| <span class="sourceLineNo">047</span> * method and the interruption flag will be set just before returning if any.<a name="line.47"></a> |
| <span class="sourceLineNo">048</span> */<a name="line.48"></a> |
| <span class="sourceLineNo">049</span> T get() {<a name="line.49"></a> |
| <span class="sourceLineNo">050</span> InstanceHolder<T> instanceHolder;<a name="line.50"></a> |
| <span class="sourceLineNo">051</span> boolean interrupted = false;<a name="line.51"></a> |
| <span class="sourceLineNo">052</span><a name="line.52"></a> |
| <span class="sourceLineNo">053</span> while ((instanceHolder = this.instanceHolder) == null) {<a name="line.53"></a> |
| <span class="sourceLineNo">054</span> try {<a name="line.54"></a> |
| <span class="sourceLineNo">055</span> pendingLatch.await();<a name="line.55"></a> |
| <span class="sourceLineNo">056</span> } catch (InterruptedException e) {<a name="line.56"></a> |
| <span class="sourceLineNo">057</span> interrupted = true;<a name="line.57"></a> |
| <span class="sourceLineNo">058</span> }<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> if (interrupted) {<a name="line.61"></a> |
| <span class="sourceLineNo">062</span> Thread.currentThread().interrupt();<a name="line.62"></a> |
| <span class="sourceLineNo">063</span> }<a name="line.63"></a> |
| <span class="sourceLineNo">064</span> return instanceHolder.instance;<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> /**<a name="line.67"></a> |
| <span class="sourceLineNo">068</span> * Associates the given instance for the method {@link #get}. This method should be called once,<a name="line.68"></a> |
| <span class="sourceLineNo">069</span> * and {@code instance} should be non-null. This method is expected to call as soon as possible<a name="line.69"></a> |
| <span class="sourceLineNo">070</span> * because the method {@code get} is uninterruptibly blocked until this method is called.<a name="line.70"></a> |
| <span class="sourceLineNo">071</span> */<a name="line.71"></a> |
| <span class="sourceLineNo">072</span> void prepare(T instance) {<a name="line.72"></a> |
| <span class="sourceLineNo">073</span> assert instance != null;<a name="line.73"></a> |
| <span class="sourceLineNo">074</span> instanceHolder = new InstanceHolder<>(instance);<a name="line.74"></a> |
| <span class="sourceLineNo">075</span> pendingLatch.countDown();<a name="line.75"></a> |
| <span class="sourceLineNo">076</span> }<a name="line.76"></a> |
| <span class="sourceLineNo">077</span>}<a name="line.77"></a> |
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