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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 org.apache.yetus.audience.InterfaceAudience;</span> |
| <span class="source-line-no">021</span><span id="line-21"></span> |
| <span class="source-line-no">022</span><span id="line-22">/**</span> |
| <span class="source-line-no">023</span><span id="line-23"> * Manages a singleton instance of the environment edge. This class shall implement static versions</span> |
| <span class="source-line-no">024</span><span id="line-24"> * of the interface {@link EnvironmentEdge}, then defer to the delegate on invocation. <br></span> |
| <span class="source-line-no">025</span><span id="line-25"> * <b>Original Motivation:</b> The main purpose of the Environment Edge Manager was to have better</span> |
| <span class="source-line-no">026</span><span id="line-26"> * control over the tests so that they behave the same when run in any system. (Refer:</span> |
| <span class="source-line-no">027</span><span id="line-27"> * <a href="https://issues.apache.org/jira/browse/HBASE-2578">HBASE-2578</a> - The issue which added</span> |
| <span class="source-line-no">028</span><span id="line-28"> * the {@link org.apache.hadoop.hbase.util.EnvironmentEdgeManager}). The idea is to have a central</span> |
| <span class="source-line-no">029</span><span id="line-29"> * place where time can be assigned in HBase. That makes it easier to inject different</span> |
| <span class="source-line-no">030</span><span id="line-30"> * implementations of time. The default environment edge is the Java Current Time in millis. The</span> |
| <span class="source-line-no">031</span><span id="line-31"> * environment edge manager class is designed to be able to plug in a new implementation of time by</span> |
| <span class="source-line-no">032</span><span id="line-32"> * simply injecting an implementation of {@link org.apache.hadoop.hbase.util.EnvironmentEdge}</span> |
| <span class="source-line-no">033</span><span id="line-33"> * interface to {@link org.apache.hadoop.hbase.util.EnvironmentEdgeManager}</span> |
| <span class="source-line-no">034</span><span id="line-34"> * <p></span> |
| <span class="source-line-no">035</span><span id="line-35"> * <b>Problems with Environment Edge:</b><br></span> |
| <span class="source-line-no">036</span><span id="line-36"> * 1. One of the major problems is the side effects of injecting an Environment Edge into</span> |
| <span class="source-line-no">037</span><span id="line-37"> * Environment Edge Manager.<br></span> |
| <span class="source-line-no">038</span><span id="line-38"> * For example, A test could inject an edge to fast forward time in order to avoid thread sleep to</span> |
| <span class="source-line-no">039</span><span id="line-39"> * save time, but it could trigger a premature waking up of another thread waiting on a condition</span> |
| <span class="source-line-no">040</span><span id="line-40"> * dependent on time lapse, which could potentially affect the normal working of the system leading</span> |
| <span class="source-line-no">041</span><span id="line-41"> * to failure of tests.<br></span> |
| <span class="source-line-no">042</span><span id="line-42"> * 2. Every test should ensure it is setting the Environment Edge it needs for the test to perform</span> |
| <span class="source-line-no">043</span><span id="line-43"> * in an expected way. Because another test which might have run before the current test could have</span> |
| <span class="source-line-no">044</span><span id="line-44"> * injected its own custom Environment Edge which may not be applicable to this test. This is still</span> |
| <span class="source-line-no">045</span><span id="line-45"> * solvable but the problem is that the tests can run in parallel leading to different combinations</span> |
| <span class="source-line-no">046</span><span id="line-46"> * of environment edges being injected causing unexpected results.<br></span> |
| <span class="source-line-no">047</span><span id="line-47"> * 3. Another important issue with respect to injecting time through Environment Edge is that the</span> |
| <span class="source-line-no">048</span><span id="line-48"> * milliseconds unit of time is ingrained throughout the codebase in the form of hardcoded sleep</span> |
| <span class="source-line-no">049</span><span id="line-49"> * time or timeouts that any change of time unit or making it fast or slow can potentially trigger</span> |
| <span class="source-line-no">050</span><span id="line-50"> * unexpected failures due to timeout or unintended flow of execution.<br></span> |
| <span class="source-line-no">051</span><span id="line-51"> * </p></span> |
| <span class="source-line-no">052</span><span id="line-52"> * Because of the above issues, only {@link org.apache.hadoop.hbase.util.DefaultEnvironmentEdge} is</span> |
| <span class="source-line-no">053</span><span id="line-53"> * being used, whose implementation of time returns the {@link System#currentTimeMillis()}. It is</span> |
| <span class="source-line-no">054</span><span id="line-54"> * advised not to inject any other {@link org.apache.hadoop.hbase.util.EnvironmentEdge}.</span> |
| <span class="source-line-no">055</span><span id="line-55"> */</span> |
| <span class="source-line-no">056</span><span id="line-56">@InterfaceAudience.Private</span> |
| <span class="source-line-no">057</span><span id="line-57">public class EnvironmentEdgeManager {</span> |
| <span class="source-line-no">058</span><span id="line-58"> private static volatile EnvironmentEdge delegate = new DefaultEnvironmentEdge();</span> |
| <span class="source-line-no">059</span><span id="line-59"></span> |
| <span class="source-line-no">060</span><span id="line-60"> private EnvironmentEdgeManager() {</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"></span> |
| <span class="source-line-no">064</span><span id="line-64"> /**</span> |
| <span class="source-line-no">065</span><span id="line-65"> * Retrieves the singleton instance of the {@link EnvironmentEdge} that is being managed.</span> |
| <span class="source-line-no">066</span><span id="line-66"> * @return the edge.</span> |
| <span class="source-line-no">067</span><span id="line-67"> */</span> |
| <span class="source-line-no">068</span><span id="line-68"> public static EnvironmentEdge getDelegate() {</span> |
| <span class="source-line-no">069</span><span id="line-69"> return delegate;</span> |
| <span class="source-line-no">070</span><span id="line-70"> }</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"> * Resets the managed instance to the default instance: {@link DefaultEnvironmentEdge}.</span> |
| <span class="source-line-no">074</span><span id="line-74"> */</span> |
| <span class="source-line-no">075</span><span id="line-75"> public static void reset() {</span> |
| <span class="source-line-no">076</span><span id="line-76"> injectEdge(new DefaultEnvironmentEdge());</span> |
| <span class="source-line-no">077</span><span id="line-77"> }</span> |
| <span class="source-line-no">078</span><span id="line-78"></span> |
| <span class="source-line-no">079</span><span id="line-79"> /**</span> |
| <span class="source-line-no">080</span><span id="line-80"> * Injects the given edge such that it becomes the managed entity. If null is passed to this</span> |
| <span class="source-line-no">081</span><span id="line-81"> * method, the default type is assigned to the delegate.</span> |
| <span class="source-line-no">082</span><span id="line-82"> * @param edge the new edge.</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 static void injectEdge(EnvironmentEdge edge) {</span> |
| <span class="source-line-no">085</span><span id="line-85"> if (edge == null) {</span> |
| <span class="source-line-no">086</span><span id="line-86"> reset();</span> |
| <span class="source-line-no">087</span><span id="line-87"> } else {</span> |
| <span class="source-line-no">088</span><span id="line-88"> delegate = edge;</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"></span> |
| <span class="source-line-no">092</span><span id="line-92"> /**</span> |
| <span class="source-line-no">093</span><span id="line-93"> * Defers to the delegate and calls the {@link EnvironmentEdge#currentTime()} method.</span> |
| <span class="source-line-no">094</span><span id="line-94"> * @return current time in millis according to the delegate.</span> |
| <span class="source-line-no">095</span><span id="line-95"> */</span> |
| <span class="source-line-no">096</span><span id="line-96"> public static long currentTime() {</span> |
| <span class="source-line-no">097</span><span id="line-97"> return getDelegate().currentTime();</span> |
| <span class="source-line-no">098</span><span id="line-98"> }</span> |
| <span class="source-line-no">099</span><span id="line-99">}</span> |
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| </pre> |
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