001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements. See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership. The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License. You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018 package org.apache.hadoop.util;
019
020 import org.apache.commons.logging.Log;
021 import org.apache.commons.logging.LogFactory;
022
023 import java.util.ArrayList;
024 import java.util.Collections;
025 import java.util.Comparator;
026 import java.util.HashSet;
027 import java.util.List;
028 import java.util.Set;
029 import java.util.concurrent.atomic.AtomicBoolean;
030
031 /**
032 * The <code>ShutdownHookManager</code> enables running shutdownHook
033 * in a deterministic order, higher priority first.
034 * <p/>
035 * The JVM runs ShutdownHooks in a non-deterministic order or in parallel.
036 * This class registers a single JVM shutdownHook and run all the
037 * shutdownHooks registered to it (to this class) in order based on their
038 * priority.
039 */
040 public class ShutdownHookManager {
041
042 private static final ShutdownHookManager MGR = new ShutdownHookManager();
043
044 private static final Log LOG = LogFactory.getLog(ShutdownHookManager.class);
045
046 static {
047 Runtime.getRuntime().addShutdownHook(
048 new Thread() {
049 @Override
050 public void run() {
051 MGR.shutdownInProgress.set(true);
052 for (Runnable hook: MGR.getShutdownHooksInOrder()) {
053 try {
054 hook.run();
055 } catch (Throwable ex) {
056 LOG.warn("ShutdownHook '" + hook.getClass().getSimpleName() +
057 "' failed, " + ex.toString(), ex);
058 }
059 }
060 }
061 }
062 );
063 }
064
065 /**
066 * Return <code>ShutdownHookManager</code> singleton.
067 *
068 * @return <code>ShutdownHookManager</code> singleton.
069 */
070 public static ShutdownHookManager get() {
071 return MGR;
072 }
073
074 /**
075 * Private structure to store ShutdownHook and its priority.
076 */
077 private static class HookEntry {
078 Runnable hook;
079 int priority;
080
081 public HookEntry(Runnable hook, int priority) {
082 this.hook = hook;
083 this.priority = priority;
084 }
085
086 @Override
087 public int hashCode() {
088 return hook.hashCode();
089 }
090
091 @Override
092 public boolean equals(Object obj) {
093 boolean eq = false;
094 if (obj != null) {
095 if (obj instanceof HookEntry) {
096 eq = (hook == ((HookEntry)obj).hook);
097 }
098 }
099 return eq;
100 }
101
102 }
103
104 private Set<HookEntry> hooks =
105 Collections.synchronizedSet(new HashSet<HookEntry>());
106
107 private AtomicBoolean shutdownInProgress = new AtomicBoolean(false);
108
109 //private to constructor to ensure singularity
110 private ShutdownHookManager() {
111 }
112
113 /**
114 * Returns the list of shutdownHooks in order of execution,
115 * Highest priority first.
116 *
117 * @return the list of shutdownHooks in order of execution.
118 */
119 List<Runnable> getShutdownHooksInOrder() {
120 List<HookEntry> list;
121 synchronized (MGR.hooks) {
122 list = new ArrayList<HookEntry>(MGR.hooks);
123 }
124 Collections.sort(list, new Comparator<HookEntry>() {
125
126 //reversing comparison so highest priority hooks are first
127 @Override
128 public int compare(HookEntry o1, HookEntry o2) {
129 return o2.priority - o1.priority;
130 }
131 });
132 List<Runnable> ordered = new ArrayList<Runnable>();
133 for (HookEntry entry: list) {
134 ordered.add(entry.hook);
135 }
136 return ordered;
137 }
138
139 /**
140 * Adds a shutdownHook with a priority, the higher the priority
141 * the earlier will run. ShutdownHooks with same priority run
142 * in a non-deterministic order.
143 *
144 * @param shutdownHook shutdownHook <code>Runnable</code>
145 * @param priority priority of the shutdownHook.
146 */
147 public void addShutdownHook(Runnable shutdownHook, int priority) {
148 if (shutdownHook == null) {
149 throw new IllegalArgumentException("shutdownHook cannot be NULL");
150 }
151 if (shutdownInProgress.get()) {
152 throw new IllegalStateException("Shutdown in progress, cannot add a shutdownHook");
153 }
154 hooks.add(new HookEntry(shutdownHook, priority));
155 }
156
157 /**
158 * Removes a shutdownHook.
159 *
160 * @param shutdownHook shutdownHook to remove.
161 * @return TRUE if the shutdownHook was registered and removed,
162 * FALSE otherwise.
163 */
164 public boolean removeShutdownHook(Runnable shutdownHook) {
165 if (shutdownInProgress.get()) {
166 throw new IllegalStateException("Shutdown in progress, cannot remove a shutdownHook");
167 }
168 return hooks.remove(new HookEntry(shutdownHook, 0));
169 }
170
171 /**
172 * Indicates if a shutdownHook is registered or not.
173 *
174 * @param shutdownHook shutdownHook to check if registered.
175 * @return TRUE/FALSE depending if the shutdownHook is is registered.
176 */
177 public boolean hasShutdownHook(Runnable shutdownHook) {
178 return hooks.contains(new HookEntry(shutdownHook, 0));
179 }
180
181 /**
182 * Indicates if shutdown is in progress or not.
183 *
184 * @return TRUE if the shutdown is in progress, otherwise FALSE.
185 */
186 public boolean isShutdownInProgress() {
187 return shutdownInProgress.get();
188 }
189
190 }