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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.master;<a name="line.18"></a>
<span class="sourceLineNo">019</span><a name="line.19"></a>
<span class="sourceLineNo">020</span>import java.io.IOException;<a name="line.20"></a>
<span class="sourceLineNo">021</span>import java.util.concurrent.atomic.AtomicBoolean;<a name="line.21"></a>
<span class="sourceLineNo">022</span>import java.util.concurrent.atomic.AtomicInteger;<a name="line.22"></a>
<span class="sourceLineNo">023</span>import org.apache.hadoop.conf.Configuration;<a name="line.23"></a>
<span class="sourceLineNo">024</span>import org.apache.hadoop.fs.FileSystem;<a name="line.24"></a>
<span class="sourceLineNo">025</span>import org.apache.hadoop.fs.Path;<a name="line.25"></a>
<span class="sourceLineNo">026</span>import org.apache.hadoop.hbase.ClusterId;<a name="line.26"></a>
<span class="sourceLineNo">027</span>import org.apache.hadoop.hbase.Server;<a name="line.27"></a>
<span class="sourceLineNo">028</span>import org.apache.hadoop.hbase.util.CommonFSUtils;<a name="line.28"></a>
<span class="sourceLineNo">029</span>import org.apache.hadoop.hbase.util.FSUtils;<a name="line.29"></a>
<span class="sourceLineNo">030</span>import org.apache.yetus.audience.InterfaceAudience;<a name="line.30"></a>
<span class="sourceLineNo">031</span>import org.slf4j.Logger;<a name="line.31"></a>
<span class="sourceLineNo">032</span>import org.slf4j.LoggerFactory;<a name="line.32"></a>
<span class="sourceLineNo">033</span><a name="line.33"></a>
<span class="sourceLineNo">034</span>import org.apache.hbase.thirdparty.com.google.common.base.Preconditions;<a name="line.34"></a>
<span class="sourceLineNo">035</span><a name="line.35"></a>
<span class="sourceLineNo">036</span>/**<a name="line.36"></a>
<span class="sourceLineNo">037</span> * Caches the cluster ID of the cluster. For standby masters, this is used to serve the client RPCs<a name="line.37"></a>
<span class="sourceLineNo">038</span> * that fetch the cluster ID. ClusterID is only created by an active master if one does not already<a name="line.38"></a>
<span class="sourceLineNo">039</span> * exist. Standby masters just read the information from the file system. This class is thread-safe.<a name="line.39"></a>
<span class="sourceLineNo">040</span> * TODO: Make it a singleton without affecting concurrent junit tests.<a name="line.40"></a>
<span class="sourceLineNo">041</span> */<a name="line.41"></a>
<span class="sourceLineNo">042</span>@InterfaceAudience.Private<a name="line.42"></a>
<span class="sourceLineNo">043</span>public class CachedClusterId {<a name="line.43"></a>
<span class="sourceLineNo">044</span><a name="line.44"></a>
<span class="sourceLineNo">045</span> public static final Logger LOG = LoggerFactory.getLogger(CachedClusterId.class);<a name="line.45"></a>
<span class="sourceLineNo">046</span> private static final int MAX_FETCH_TIMEOUT_MS = 10000;<a name="line.46"></a>
<span class="sourceLineNo">047</span><a name="line.47"></a>
<span class="sourceLineNo">048</span> private final Path rootDir;<a name="line.48"></a>
<span class="sourceLineNo">049</span> private final FileSystem fs;<a name="line.49"></a>
<span class="sourceLineNo">050</span><a name="line.50"></a>
<span class="sourceLineNo">051</span> // When true, indicates that a FileSystem fetch of ClusterID is in progress. This is used to<a name="line.51"></a>
<span class="sourceLineNo">052</span> // avoid multiple fetches from FS and let only one thread fetch the information.<a name="line.52"></a>
<span class="sourceLineNo">053</span> AtomicBoolean fetchInProgress = new AtomicBoolean(false);<a name="line.53"></a>
<span class="sourceLineNo">054</span><a name="line.54"></a>
<span class="sourceLineNo">055</span> // When true, it means that the cluster ID has been fetched successfully from fs.<a name="line.55"></a>
<span class="sourceLineNo">056</span> private AtomicBoolean isClusterIdSet = new AtomicBoolean(false);<a name="line.56"></a>
<span class="sourceLineNo">057</span> // Immutable once set and read multiple times.<a name="line.57"></a>
<span class="sourceLineNo">058</span> private ClusterId clusterId;<a name="line.58"></a>
<span class="sourceLineNo">059</span><a name="line.59"></a>
<span class="sourceLineNo">060</span> private final Server server;<a name="line.60"></a>
<span class="sourceLineNo">061</span><a name="line.61"></a>
<span class="sourceLineNo">062</span> // cache stats for testing.<a name="line.62"></a>
<span class="sourceLineNo">063</span> private AtomicInteger cacheMisses = new AtomicInteger(0);<a name="line.63"></a>
<span class="sourceLineNo">064</span><a name="line.64"></a>
<span class="sourceLineNo">065</span> public CachedClusterId(Server server, Configuration conf) throws IOException {<a name="line.65"></a>
<span class="sourceLineNo">066</span> this.rootDir = CommonFSUtils.getRootDir(conf);<a name="line.66"></a>
<span class="sourceLineNo">067</span> this.fs = rootDir.getFileSystem(conf);<a name="line.67"></a>
<span class="sourceLineNo">068</span> this.server = server;<a name="line.68"></a>
<span class="sourceLineNo">069</span> }<a name="line.69"></a>
<span class="sourceLineNo">070</span><a name="line.70"></a>
<span class="sourceLineNo">071</span> /**<a name="line.71"></a>
<span class="sourceLineNo">072</span> * Succeeds only once, when setting to a non-null value. Overwrites are not allowed.<a name="line.72"></a>
<span class="sourceLineNo">073</span> */<a name="line.73"></a>
<span class="sourceLineNo">074</span> private void setClusterId(ClusterId id) {<a name="line.74"></a>
<span class="sourceLineNo">075</span> if (id == null || isClusterIdSet.get()) {<a name="line.75"></a>
<span class="sourceLineNo">076</span> return;<a name="line.76"></a>
<span class="sourceLineNo">077</span> }<a name="line.77"></a>
<span class="sourceLineNo">078</span> clusterId = id;<a name="line.78"></a>
<span class="sourceLineNo">079</span> isClusterIdSet.set(true);<a name="line.79"></a>
<span class="sourceLineNo">080</span> }<a name="line.80"></a>
<span class="sourceLineNo">081</span><a name="line.81"></a>
<span class="sourceLineNo">082</span> /**<a name="line.82"></a>
<span class="sourceLineNo">083</span> * Returns a cached copy of the cluster ID. null if the cache is not populated.<a name="line.83"></a>
<span class="sourceLineNo">084</span> */<a name="line.84"></a>
<span class="sourceLineNo">085</span> private String getClusterId() {<a name="line.85"></a>
<span class="sourceLineNo">086</span> if (!isClusterIdSet.get()) {<a name="line.86"></a>
<span class="sourceLineNo">087</span> return null;<a name="line.87"></a>
<span class="sourceLineNo">088</span> }<a name="line.88"></a>
<span class="sourceLineNo">089</span> // It is ok to read without a lock since clusterId is immutable once set.<a name="line.89"></a>
<span class="sourceLineNo">090</span> return clusterId.toString();<a name="line.90"></a>
<span class="sourceLineNo">091</span> }<a name="line.91"></a>
<span class="sourceLineNo">092</span><a name="line.92"></a>
<span class="sourceLineNo">093</span> /**<a name="line.93"></a>
<span class="sourceLineNo">094</span> * Attempts to fetch the cluster ID from the file system. If no attempt is already in progress,<a name="line.94"></a>
<span class="sourceLineNo">095</span> * synchronously fetches the cluster ID and sets it. If an attempt is already in progress, returns<a name="line.95"></a>
<span class="sourceLineNo">096</span> * right away and the caller is expected to wait for the fetch to finish.<a name="line.96"></a>
<span class="sourceLineNo">097</span> * @return true if the attempt is done, false if another thread is already fetching it.<a name="line.97"></a>
<span class="sourceLineNo">098</span> */<a name="line.98"></a>
<span class="sourceLineNo">099</span> private boolean attemptFetch() {<a name="line.99"></a>
<span class="sourceLineNo">100</span> if (fetchInProgress.compareAndSet(false, true)) {<a name="line.100"></a>
<span class="sourceLineNo">101</span> // A fetch is not in progress, so try fetching the cluster ID synchronously and then notify<a name="line.101"></a>
<span class="sourceLineNo">102</span> // the waiting threads.<a name="line.102"></a>
<span class="sourceLineNo">103</span> try {<a name="line.103"></a>
<span class="sourceLineNo">104</span> cacheMisses.incrementAndGet();<a name="line.104"></a>
<span class="sourceLineNo">105</span> setClusterId(FSUtils.getClusterId(fs, rootDir));<a name="line.105"></a>
<span class="sourceLineNo">106</span> } catch (IOException e) {<a name="line.106"></a>
<span class="sourceLineNo">107</span> LOG.warn("Error fetching cluster ID", e);<a name="line.107"></a>
<span class="sourceLineNo">108</span> } finally {<a name="line.108"></a>
<span class="sourceLineNo">109</span> Preconditions.checkState(fetchInProgress.compareAndSet(true, false));<a name="line.109"></a>
<span class="sourceLineNo">110</span> synchronized (fetchInProgress) {<a name="line.110"></a>
<span class="sourceLineNo">111</span> fetchInProgress.notifyAll();<a name="line.111"></a>
<span class="sourceLineNo">112</span> }<a name="line.112"></a>
<span class="sourceLineNo">113</span> }<a name="line.113"></a>
<span class="sourceLineNo">114</span> return true;<a name="line.114"></a>
<span class="sourceLineNo">115</span> }<a name="line.115"></a>
<span class="sourceLineNo">116</span> return false;<a name="line.116"></a>
<span class="sourceLineNo">117</span> }<a name="line.117"></a>
<span class="sourceLineNo">118</span><a name="line.118"></a>
<span class="sourceLineNo">119</span> private void waitForFetchToFinish() throws InterruptedException {<a name="line.119"></a>
<span class="sourceLineNo">120</span> synchronized (fetchInProgress) {<a name="line.120"></a>
<span class="sourceLineNo">121</span> while (fetchInProgress.get()) {<a name="line.121"></a>
<span class="sourceLineNo">122</span> // We don't want the fetches to block forever, for example if there are bugs<a name="line.122"></a>
<span class="sourceLineNo">123</span> // of missing notifications.<a name="line.123"></a>
<span class="sourceLineNo">124</span> fetchInProgress.wait(MAX_FETCH_TIMEOUT_MS);<a name="line.124"></a>
<span class="sourceLineNo">125</span> }<a name="line.125"></a>
<span class="sourceLineNo">126</span> }<a name="line.126"></a>
<span class="sourceLineNo">127</span> }<a name="line.127"></a>
<span class="sourceLineNo">128</span><a name="line.128"></a>
<span class="sourceLineNo">129</span> /**<a name="line.129"></a>
<span class="sourceLineNo">130</span> * Fetches the ClusterId from FS if it is not cached locally. Atomically updates the cached copy<a name="line.130"></a>
<span class="sourceLineNo">131</span> * and is thread-safe. Optimized to do a single fetch when there are multiple threads are trying<a name="line.131"></a>
<span class="sourceLineNo">132</span> * get from a clean cache.<a name="line.132"></a>
<span class="sourceLineNo">133</span> * @return ClusterId by reading from FileSystem or null in any error case or cluster ID does not<a name="line.133"></a>
<span class="sourceLineNo">134</span> * exist on the file system or if the server initiated a tear down.<a name="line.134"></a>
<span class="sourceLineNo">135</span> */<a name="line.135"></a>
<span class="sourceLineNo">136</span> public String getFromCacheOrFetch() {<a name="line.136"></a>
<span class="sourceLineNo">137</span> if (server.isStopping() || server.isStopped()) {<a name="line.137"></a>
<span class="sourceLineNo">138</span> return null;<a name="line.138"></a>
<span class="sourceLineNo">139</span> }<a name="line.139"></a>
<span class="sourceLineNo">140</span> String id = getClusterId();<a name="line.140"></a>
<span class="sourceLineNo">141</span> if (id != null) {<a name="line.141"></a>
<span class="sourceLineNo">142</span> return id;<a name="line.142"></a>
<span class="sourceLineNo">143</span> }<a name="line.143"></a>
<span class="sourceLineNo">144</span> if (!attemptFetch()) {<a name="line.144"></a>
<span class="sourceLineNo">145</span> // A fetch is in progress.<a name="line.145"></a>
<span class="sourceLineNo">146</span> try {<a name="line.146"></a>
<span class="sourceLineNo">147</span> waitForFetchToFinish();<a name="line.147"></a>
<span class="sourceLineNo">148</span> } catch (InterruptedException e) {<a name="line.148"></a>
<span class="sourceLineNo">149</span> // pass and return whatever is in the cache.<a name="line.149"></a>
<span class="sourceLineNo">150</span> }<a name="line.150"></a>
<span class="sourceLineNo">151</span> }<a name="line.151"></a>
<span class="sourceLineNo">152</span> return getClusterId();<a name="line.152"></a>
<span class="sourceLineNo">153</span> }<a name="line.153"></a>
<span class="sourceLineNo">154</span><a name="line.154"></a>
<span class="sourceLineNo">155</span> public int getCacheStats() {<a name="line.155"></a>
<span class="sourceLineNo">156</span> return cacheMisses.get();<a name="line.156"></a>
<span class="sourceLineNo">157</span> }<a name="line.157"></a>
<span class="sourceLineNo">158</span>}<a name="line.158"></a>
</pre>
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