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1   /**
2    * Copyright 2011 The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *     http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  package org.apache.hadoop.hbase.monitoring;
21  
22  import java.io.PrintWriter;
23  import java.lang.ref.WeakReference;
24  import java.lang.reflect.InvocationHandler;
25  import java.lang.reflect.Method;
26  import java.lang.reflect.Proxy;
27  import java.util.ArrayList;
28  import java.util.Iterator;
29  import java.util.List;
30  
31  import org.apache.commons.collections.buffer.CircularFifoBuffer;
32  import org.apache.commons.logging.Log;
33  import org.apache.commons.logging.LogFactory;
34  
35  import com.google.common.annotations.VisibleForTesting;
36  import com.google.common.collect.Lists;
37  
38  /**
39   * Singleton which keeps track of tasks going on in this VM.
40   * A Task here is anything which takes more than a few seconds
41   * and the user might want to inquire about the status
42   */
43  public class TaskMonitor {
44    private static final Log LOG = LogFactory.getLog(TaskMonitor.class);
45  
46    // Don't keep around any tasks that have completed more than
47    // 60 seconds ago
48    private static final long EXPIRATION_TIME = 60*1000;
49  
50    @VisibleForTesting
51    static final int MAX_TASKS = 1000;
52    
53    private static TaskMonitor instance;
54    private CircularFifoBuffer tasks = new CircularFifoBuffer(MAX_TASKS);
55  
56    /**
57     * Get singleton instance.
58     * TODO this would be better off scoped to a single daemon
59     */
60    public static synchronized TaskMonitor get() {
61      if (instance == null) {
62        instance = new TaskMonitor();
63      }
64      return instance;
65    }
66    
67    public synchronized MonitoredTask createStatus(String description) {
68      MonitoredTask stat = new MonitoredTaskImpl();
69      stat.setDescription(description);
70      MonitoredTask proxy = (MonitoredTask) Proxy.newProxyInstance(
71          stat.getClass().getClassLoader(),
72          new Class<?>[] { MonitoredTask.class },
73          new PassthroughInvocationHandler<MonitoredTask>(stat));
74      TaskAndWeakRefPair pair = new TaskAndWeakRefPair(stat, proxy);
75      tasks.add(pair);
76      return proxy;
77    }
78  
79    public synchronized MonitoredRPCHandler createRPCStatus(String description) {
80      MonitoredRPCHandler stat = new MonitoredRPCHandlerImpl();
81      stat.setDescription(description);
82      MonitoredRPCHandler proxy = (MonitoredRPCHandler) Proxy.newProxyInstance(
83          stat.getClass().getClassLoader(),
84          new Class<?>[] { MonitoredRPCHandler.class },
85          new PassthroughInvocationHandler<MonitoredRPCHandler>(stat));
86      TaskAndWeakRefPair pair = new TaskAndWeakRefPair(stat, proxy);
87      tasks.add(pair);
88      return proxy;
89    }
90  
91    private synchronized void purgeExpiredTasks() {
92      for (Iterator<TaskAndWeakRefPair> it = tasks.iterator();
93           it.hasNext();) {
94        TaskAndWeakRefPair pair = it.next();
95        MonitoredTask stat = pair.get();
96        
97        if (pair.isDead()) {
98          // The class who constructed this leaked it. So we can
99          // assume it's done.
100         if (stat.getState() == MonitoredTaskImpl.State.RUNNING) {
101           LOG.warn("Status " + stat + " appears to have been leaked");
102           stat.cleanup();
103         }
104       }
105       
106       if (canPurge(stat)) {
107         it.remove();
108       }
109     }
110   }
111 
112   /**
113    * Produces a list containing copies of the current state of all non-expired 
114    * MonitoredTasks handled by this TaskMonitor.
115    * @return A complete list of MonitoredTasks.
116    */
117   public synchronized List<MonitoredTask> getTasks() {
118     purgeExpiredTasks();
119     ArrayList<MonitoredTask> ret = Lists.newArrayListWithCapacity(tasks.size());
120     for (Iterator<TaskAndWeakRefPair> it = tasks.iterator();
121          it.hasNext();) {
122       TaskAndWeakRefPair pair = it.next();
123       MonitoredTask t = pair.get();
124       ret.add(t.clone());
125     }
126     return ret;
127   }
128 
129   private boolean canPurge(MonitoredTask stat) {
130     long cts = stat.getCompletionTimestamp();
131     return (cts > 0 && System.currentTimeMillis() - cts > EXPIRATION_TIME);
132   }
133   
134 
135   public void dumpAsText(PrintWriter out) {
136     long now = System.currentTimeMillis();
137     
138     List<MonitoredTask> tasks = getTasks();
139     for (MonitoredTask task : tasks) {
140       out.println("Task: " + task.getDescription());
141       out.println("Status: " + task.getState() + ":" + task.getStatus());
142       long running = (now - task.getStartTime())/1000;
143       if (task.getCompletionTimestamp() != -1) {
144         long completed = (now - task.getCompletionTimestamp()) / 1000;
145         out.println("Completed " + completed + "s ago");
146         out.println("Ran for " +
147             (task.getCompletionTimestamp() - task.getStartTime())/1000
148             + "s");
149       } else {
150         out.println("Running for " + running + "s");
151       }
152       out.println();
153     }
154   }
155 
156   /**
157    * This class encapsulates an object as well as a weak reference to a proxy
158    * that passes through calls to that object. In art form:
159    * <code>
160    *     Proxy  <------------------
161    *       |                       \
162    *       v                        \
163    * PassthroughInvocationHandler   |  weak reference
164    *       |                       /
165    * MonitoredTaskImpl            / 
166    *       |                     /
167    * StatAndWeakRefProxy  ------/
168    *
169    * Since we only return the Proxy to the creator of the MonitorableStatus,
170    * this means that they can leak that object, and we'll detect it
171    * since our weak reference will go null. But, we still have the actual
172    * object, so we can log it and display it as a leaked (incomplete) action.
173    */
174   private static class TaskAndWeakRefPair {
175     private MonitoredTask impl;
176     private WeakReference<MonitoredTask> weakProxy;
177     
178     public TaskAndWeakRefPair(MonitoredTask stat,
179         MonitoredTask proxy) {
180       this.impl = stat;
181       this.weakProxy = new WeakReference<MonitoredTask>(proxy);
182     }
183     
184     public MonitoredTask get() {
185       return impl;
186     }
187     
188     public boolean isDead() {
189       return weakProxy.get() == null;
190     }
191   }
192   
193   /**
194    * An InvocationHandler that simply passes through calls to the original 
195    * object.
196    */
197   private static class PassthroughInvocationHandler<T> implements InvocationHandler {
198     private T delegatee;
199     
200     public PassthroughInvocationHandler(T delegatee) {
201       this.delegatee = delegatee;
202     }
203 
204     @Override
205     public Object invoke(Object proxy, Method method, Object[] args)
206         throws Throwable {
207       return method.invoke(delegatee, args);
208     }    
209   }
210 }