1 | /*
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2 | * Copyright 2001-2004 The Apache Software Foundation
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3 | *
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4 | * Licensed under the Apache License, Version 2.0 (the "License");
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5 | * you may not use this file except in compliance with the License.
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6 | * You may obtain a copy of the License at
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7 | *
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8 | * http://www.apache.org/licenses/LICENSE-2.0
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9 | *
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10 | * Unless required by applicable law or agreed to in writing, software
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11 | * distributed under the License is distributed on an "AS IS" BASIS,
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12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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13 | * See the License for the specific language governing permissions and
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14 | * limitations under the License.
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15 | *
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16 | */
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17 |
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18 | package org.apache.tools.ant.taskdefs;
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19 |
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20 | import java.lang.reflect.InvocationTargetException;
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21 | import java.lang.reflect.Method;
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22 | import java.util.Enumeration;
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23 | import java.util.Vector;
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24 |
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25 | /**
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26 | * Destroys all registered <code>Process</code>es when the VM exits.
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27 | *
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28 | * @since Ant 1.5
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29 | */
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30 | class ProcessDestroyer implements Runnable {
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31 |
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32 | private Vector processes = new Vector();
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33 | // methods to register and unregister shutdown hooks
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34 | private Method addShutdownHookMethod;
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35 | private Method removeShutdownHookMethod;
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36 | private ProcessDestroyerImpl destroyProcessThread = null;
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37 |
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38 | // whether or not this ProcessDestroyer has been registered as a
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39 | // shutdown hook
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40 | private boolean added = false;
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41 | // whether or not this ProcessDestroyer is currently running as
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42 | // shutdown hook
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43 | private boolean running = false;
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44 |
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45 | private class ProcessDestroyerImpl extends Thread {
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46 | private boolean shouldDestroy = true;
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47 |
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48 | public ProcessDestroyerImpl() {
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49 | super("ProcessDestroyer Shutdown Hook");
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50 | }
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51 | public void run() {
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52 | if (shouldDestroy) {
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53 | ProcessDestroyer.this.run();
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54 | }
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55 | }
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56 |
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57 | public void setShouldDestroy(boolean shouldDestroy) {
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58 | this.shouldDestroy = shouldDestroy;
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59 | }
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60 | }
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61 |
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62 | /**
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63 | * Constructs a <code>ProcessDestroyer</code> and obtains
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64 | * <code>Runtime.addShutdownHook()</code> and
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65 | * <code>Runtime.removeShutdownHook()</code> through reflection. The
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66 | * ProcessDestroyer manages a list of processes to be destroyed when the
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67 | * VM exits. If a process is added when the list is empty,
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68 | * this <code>ProcessDestroyer</code> is registered as a shutdown hook. If
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69 | * removing a process results in an empty list, the
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70 | * <code>ProcessDestroyer</code> is removed as a shutdown hook.
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71 | */
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72 | public ProcessDestroyer() {
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73 | try {
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74 | // check to see if the shutdown hook methods exists
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75 | // (support pre-JDK 1.3 VMs)
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76 | Class[] paramTypes = {Thread.class};
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77 | addShutdownHookMethod =
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78 | Runtime.class.getMethod("addShutdownHook", paramTypes);
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79 |
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80 | removeShutdownHookMethod =
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81 | Runtime.class.getMethod("removeShutdownHook", paramTypes);
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82 | // wait to add shutdown hook as needed
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83 | } catch (NoSuchMethodException e) {
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84 | // it just won't be added as a shutdown hook... :(
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85 | } catch (Exception e) {
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86 | e.printStackTrace();
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87 | }
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88 | }
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89 |
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90 | /**
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91 | * Registers this <code>ProcessDestroyer</code> as a shutdown hook,
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92 | * uses reflection to ensure pre-JDK 1.3 compatibility.
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93 | */
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94 | private void addShutdownHook() {
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95 | if (addShutdownHookMethod != null && !running) {
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96 | destroyProcessThread = new ProcessDestroyerImpl();
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97 | Object[] args = {destroyProcessThread};
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98 | try {
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99 | addShutdownHookMethod.invoke(Runtime.getRuntime(), args);
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100 | added = true;
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101 | } catch (IllegalAccessException e) {
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102 | e.printStackTrace();
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103 | } catch (InvocationTargetException e) {
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104 | Throwable t = e.getTargetException();
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105 | if (t != null && t.getClass() == IllegalStateException.class) {
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106 | // shutdown already is in progress
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107 | running = true;
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108 | } else {
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109 | e.printStackTrace();
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110 | }
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111 | }
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112 | }
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113 | }
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114 |
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115 | /**
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116 | * Removes this <code>ProcessDestroyer</code> as a shutdown hook,
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117 | * uses reflection to ensure pre-JDK 1.3 compatibility
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118 | */
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119 | private void removeShutdownHook() {
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120 | if (removeShutdownHookMethod != null && added && !running) {
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121 | Object[] args = {destroyProcessThread};
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122 | try {
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123 | Boolean removed =
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124 | (Boolean) removeShutdownHookMethod.invoke(
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125 | Runtime.getRuntime(),
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126 | args);
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127 | if (!removed.booleanValue()) {
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128 | System.err.println("Could not remove shutdown hook");
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129 | }
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130 | } catch (IllegalAccessException e) {
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131 | e.printStackTrace();
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132 | } catch (InvocationTargetException e) {
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133 | Throwable t = e.getTargetException();
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134 | if (t != null && t.getClass() == IllegalStateException.class) {
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135 | // shutdown already is in progress
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136 | running = true;
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137 | } else {
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138 | e.printStackTrace();
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139 | }
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140 | }
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141 | // start the hook thread, a unstarted thread may not be
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142 | // eligible for garbage collection
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143 | // Cf.: http://developer.java.sun.com/developer/bugParade/bugs/4533087.html
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144 | destroyProcessThread.setShouldDestroy(false);
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145 | destroyProcessThread.start();
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146 | // this should return quickly, since it basically is a NO-OP.
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147 | try {
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148 | destroyProcessThread.join(20000);
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149 | } catch (InterruptedException ie) {
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150 | // the thread didn't die in time
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151 | // it should not kill any processes unexpectedly
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152 | }
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153 | destroyProcessThread = null;
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154 | added = false;
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155 | }
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156 | }
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157 |
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158 | /**
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159 | * Returns whether or not the ProcessDestroyer is registered as
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160 | * as shutdown hook
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161 | * @return true if this is currently added as shutdown hook
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162 | */
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163 | public boolean isAddedAsShutdownHook() {
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164 | return added;
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165 | }
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166 |
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167 | /**
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168 | * Returns <code>true</code> if the specified <code>Process</code> was
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169 | * successfully added to the list of processes to destroy upon VM exit.
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170 | *
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171 | * @param process the process to add
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172 | * @return <code>true</code> if the specified <code>Process</code> was
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173 | * successfully added
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174 | */
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175 | public boolean add(Process process) {
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176 | synchronized (processes) {
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177 | // if this list is empty, register the shutdown hook
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178 | if (processes.size() == 0) {
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179 | addShutdownHook();
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180 | }
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181 | processes.addElement(process);
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182 | return processes.contains(process);
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183 | }
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184 | }
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185 |
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186 | /**
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187 | * Returns <code>true</code> if the specified <code>Process</code> was
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188 | * successfully removed from the list of processes to destroy upon VM exit.
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189 | *
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190 | * @param process the process to remove
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191 | * @return <code>true</code> if the specified <code>Process</code> was
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192 | * successfully removed
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193 | */
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194 | public boolean remove(Process process) {
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195 | synchronized (processes) {
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196 | boolean processRemoved = processes.removeElement(process);
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197 | if (processRemoved && processes.size() == 0) {
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198 | removeShutdownHook();
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199 | }
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200 | return processRemoved;
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201 | }
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202 | }
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203 |
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204 | /**
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205 | * Invoked by the VM when it is exiting.
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206 | */
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207 | public void run() {
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208 | synchronized (processes) {
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209 | running = true;
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210 | Enumeration e = processes.elements();
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211 | while (e.hasMoreElements()) {
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212 | ((Process) e.nextElement()).destroy();
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213 | }
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214 | }
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215 | }
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216 | }
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