/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package org.apache.tools.ant.taskdefs;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Enumeration;
import java.util.Vector;
/**
* Destroys all registered <code>Process</code>es when the VM exits.
*
* @since Ant 1.5
*/
class ProcessDestroyer implements Runnable {
private Vector processes = new Vector();
// methods to register and unregister shutdown hooks
private Method addShutdownHookMethod;
private Method removeShutdownHookMethod;
private ProcessDestroyerImpl destroyProcessThread = null;
// whether or not this ProcessDestroyer has been registered as a
// shutdown hook
private boolean added = false;
// whether or not this ProcessDestroyer is currently running as
// shutdown hook
private boolean running = false;
private class ProcessDestroyerImpl extends Thread {
private boolean shouldDestroy = true;
public ProcessDestroyerImpl() {
super("ProcessDestroyer Shutdown Hook");
}
public void run() {
if (shouldDestroy) {
ProcessDestroyer.this.run();
}
}
public void setShouldDestroy(boolean shouldDestroy) {
this.shouldDestroy = shouldDestroy;
}
}
/**
* Constructs a <code>ProcessDestroyer</code> and obtains
* <code>Runtime.addShutdownHook()</code> and
* <code>Runtime.removeShutdownHook()</code> through reflection. The
* ProcessDestroyer manages a list of processes to be destroyed when the
* VM exits. If a process is added when the list is empty,
* this <code>ProcessDestroyer</code> is registered as a shutdown hook. If
* removing a process results in an empty list, the
* <code>ProcessDestroyer</code> is removed as a shutdown hook.
*/
public ProcessDestroyer() {
try {
// check to see if the shutdown hook methods exists
// (support pre-JDK 1.3 VMs)
Class[] paramTypes = {Thread.class};
addShutdownHookMethod =
Runtime.class.getMethod("addShutdownHook", paramTypes);
removeShutdownHookMethod =
Runtime.class.getMethod("removeShutdownHook", paramTypes);
// wait to add shutdown hook as needed
} catch (NoSuchMethodException e) {
// it just won't be added as a shutdown hook... :(
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* Registers this <code>ProcessDestroyer</code> as a shutdown hook,
* uses reflection to ensure pre-JDK 1.3 compatibility.
*/
private void addShutdownHook() {
if (addShutdownHookMethod != null && !running) {
destroyProcessThread = new ProcessDestroyerImpl();
Object[] args = {destroyProcessThread};
try {
addShutdownHookMethod.invoke(Runtime.getRuntime(), args);
added = true;
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
Throwable t = e.getTargetException();
if (t != null && t.getClass() == IllegalStateException.class) {
// shutdown already is in progress
running = true;
} else {
e.printStackTrace();
}
}
}
}
/**
* Removes this <code>ProcessDestroyer</code> as a shutdown hook,
* uses reflection to ensure pre-JDK 1.3 compatibility
*/
private void removeShutdownHook() {
if (removeShutdownHookMethod != null && added && !running) {
Object[] args = {destroyProcessThread};
try {
Boolean removed =
(Boolean) removeShutdownHookMethod.invoke(
Runtime.getRuntime(),
args);
if (!removed.booleanValue()) {
System.err.println("Could not remove shutdown hook");
}
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
Throwable t = e.getTargetException();
if (t != null && t.getClass() == IllegalStateException.class) {
// shutdown already is in progress
running = true;
} else {
e.printStackTrace();
}
}
// start the hook thread, a unstarted thread may not be
// eligible for garbage collection
// Cf.: http://developer.java.sun.com/developer/bugParade/bugs/4533087.html
destroyProcessThread.setShouldDestroy(false);
if (!destroyProcessThread.getThreadGroup().isDestroyed()) {
// start() would throw IllegalThreadStateException from
// ThreadGroup.add if it were destroyed
destroyProcessThread.start();
}
// this should return quickly, since it basically is a NO-OP.
try {
destroyProcessThread.join(20000);
} catch (InterruptedException ie) {
// the thread didn't die in time
// it should not kill any processes unexpectedly
}
destroyProcessThread = null;
added = false;
}
}
/**
* Returns whether or not the ProcessDestroyer is registered as
* as shutdown hook
* @return true if this is currently added as shutdown hook
*/
public boolean isAddedAsShutdownHook() {
return added;
}
/**
* Returns <code>true</code> if the specified <code>Process</code> was
* successfully added to the list of processes to destroy upon VM exit.
*
* @param process the process to add
* @return <code>true</code> if the specified <code>Process</code> was
* successfully added
*/
public boolean add(Process process) {
synchronized (processes) {
// if this list is empty, register the shutdown hook
if (processes.size() == 0) {
addShutdownHook();
}
processes.addElement(process);
return processes.contains(process);
}
}
/**
* Returns <code>true</code> if the specified <code>Process</code> was
* successfully removed from the list of processes to destroy upon VM exit.
*
* @param process the process to remove
* @return <code>true</code> if the specified <code>Process</code> was
* successfully removed
*/
public boolean remove(Process process) {
synchronized (processes) {
boolean processRemoved = processes.removeElement(process);
if (processRemoved && processes.size() == 0) {
removeShutdownHook();
}
return processRemoved;
}
}
/**
* Invoked by the VM when it is exiting.
*/
public void run() {
synchronized (processes) {
running = true;
Enumeration e = processes.elements();
while (e.hasMoreElements()) {
((Process) e.nextElement()).destroy();
}
}
}
}
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