001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache license, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the license for the specific language governing permissions and
015 * limitations under the license.
016 */
017
018 package org.apache.logging.log4j.core.util;
019
020 import java.io.Serializable;
021 import java.lang.ref.Reference;
022 import java.lang.ref.SoftReference;
023 import java.lang.ref.WeakReference;
024 import java.util.Collection;
025 import java.util.concurrent.CopyOnWriteArrayList;
026 import java.util.concurrent.Executors;
027 import java.util.concurrent.ThreadFactory;
028 import java.util.concurrent.atomic.AtomicReference;
029
030 import org.apache.logging.log4j.Logger;
031 import org.apache.logging.log4j.core.LifeCycle;
032 import org.apache.logging.log4j.core.LifeCycle.State;
033 import org.apache.logging.log4j.status.StatusLogger;
034
035 /**
036 * ShutdownRegistrationStrategy that simply uses {@link Runtime#addShutdownHook(Thread)}. If no strategy is specified,
037 * this one is used for shutdown hook registration.
038 *
039 * @since 2.1
040 */
041 public class DefaultShutdownCallbackRegistry implements ShutdownCallbackRegistry, LifeCycle, Runnable, Serializable {
042
043 private static final long serialVersionUID = 1L;
044 protected static final Logger LOGGER = StatusLogger.getLogger();
045
046 private final AtomicReference<State> state = new AtomicReference<State>(State.INITIALIZED);
047 private final ThreadFactory threadFactory;
048 private final Collection<Cancellable> hooks = new CopyOnWriteArrayList<Cancellable>();
049 private Reference<Thread> shutdownHookRef;
050
051 /**
052 * Constructs a DefaultShutdownRegistrationStrategy.
053 */
054 public DefaultShutdownCallbackRegistry() {
055 this(Executors.defaultThreadFactory());
056 }
057
058 /**
059 * Constructs a DefaultShutdownRegistrationStrategy using the given {@link ThreadFactory}.
060 *
061 * @param threadFactory the ThreadFactory to use to create a {@link Runtime} shutdown hook thread
062 */
063 protected DefaultShutdownCallbackRegistry(final ThreadFactory threadFactory) {
064 this.threadFactory = threadFactory;
065 }
066
067 /**
068 * Executes the registered shutdown callbacks.
069 */
070 @Override
071 public void run() {
072 if (state.compareAndSet(State.STARTED, State.STOPPING)) {
073 for (final Runnable hook : hooks) {
074 try {
075 hook.run();
076 } catch (final Throwable t) {
077 LOGGER.error(SHUTDOWN_HOOK_MARKER, "Caught exception executing shutdown hook {}", hook, t);
078 }
079 }
080 state.set(State.STOPPED);
081 }
082 }
083
084 @Override
085 public Cancellable addShutdownCallback(final Runnable callback) {
086 if (isStarted()) {
087 final Cancellable receipt = new Cancellable() {
088 // use a reference to prevent memory leaks
089 private final Reference<Runnable> hook = new SoftReference<Runnable>(callback);
090
091 @Override
092 public void cancel() {
093 hook.clear();
094 hooks.remove(this);
095 }
096
097 @Override
098 public void run() {
099 final Runnable hook = this.hook.get();
100 if (hook != null) {
101 hook.run();
102 this.hook.clear();
103 }
104 }
105
106 @Override
107 public String toString() {
108 return String.valueOf(hook.get());
109 }
110 };
111 hooks.add(receipt);
112 return receipt;
113 }
114 throw new IllegalStateException("Cannot add new shutdown hook as this is not started. Current state: " +
115 state.get().name());
116 }
117
118 /**
119 * Registers the shutdown thread only if this is initialized.
120 */
121 @Override
122 public void start() {
123 if (state.compareAndSet(State.INITIALIZED, State.STARTING)) {
124 try {
125 addShutdownHook(threadFactory.newThread(this));
126 state.set(State.STARTED);
127 } catch (final Exception e) {
128 LOGGER.catching(e);
129 state.set(State.STOPPED);
130 }
131 }
132 }
133
134 private void addShutdownHook(final Thread thread) {
135 shutdownHookRef = new WeakReference<Thread>(thread);
136 Runtime.getRuntime().addShutdownHook(thread);
137 }
138
139 /**
140 * Cancels the shutdown thread only if this is started.
141 */
142 @Override
143 public void stop() {
144 if (state.compareAndSet(State.STARTED, State.STOPPING)) {
145 try {
146 removeShutdownHook();
147 } finally {
148 state.set(State.STOPPED);
149 }
150 }
151 }
152
153 private void removeShutdownHook() {
154 final Thread shutdownThread = shutdownHookRef.get();
155 if (shutdownThread != null) {
156 Runtime.getRuntime().removeShutdownHook(shutdownThread);
157 shutdownHookRef.enqueue();
158 }
159 }
160
161 @Override
162 public State getState() {
163 return state.get();
164 }
165
166 /**
167 * Indicates if this can accept shutdown hooks.
168 *
169 * @return true if this can accept shutdown hooks
170 */
171 @Override
172 public boolean isStarted() {
173 return state.get() == State.STARTED;
174 }
175
176 @Override
177 public boolean isStopped() {
178 return state.get() == State.STOPPED;
179 }
180
181 }