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.status.StatusLogger;
033    
034    /**
035     * ShutdownRegistrationStrategy that simply uses {@link Runtime#addShutdownHook(Thread)}. If no strategy is specified,
036     * this one is used for shutdown hook registration.
037     *
038     * @since 2.1
039     */
040    public class DefaultShutdownCallbackRegistry implements ShutdownCallbackRegistry, LifeCycle, Runnable, Serializable {
041    
042        private static final long serialVersionUID = 1L;
043        protected static final Logger LOGGER = StatusLogger.getLogger();
044    
045        private final AtomicReference<State> state = new AtomicReference<State>(State.INITIALIZED);
046        private final ThreadFactory threadFactory;
047        private final Collection<Cancellable> hooks = new CopyOnWriteArrayList<Cancellable>();
048        private Reference<Thread> shutdownHookRef;
049    
050        /**
051         * Constructs a DefaultShutdownRegistrationStrategy.
052         */
053        public DefaultShutdownCallbackRegistry() {
054            this(Executors.defaultThreadFactory());
055        }
056    
057        /**
058         * Constructs a DefaultShutdownRegistrationStrategy using the given {@link ThreadFactory}.
059         *
060         * @param threadFactory the ThreadFactory to use to create a {@link Runtime} shutdown hook thread
061         */
062        protected DefaultShutdownCallbackRegistry(final ThreadFactory threadFactory) {
063            this.threadFactory = threadFactory;
064        }
065    
066        /**
067         * Executes the registered shutdown callbacks.
068         */
069        @Override
070        public void run() {
071            if (state.compareAndSet(State.STARTED, State.STOPPING)) {
072                for (final Runnable hook : hooks) {
073                    try {
074                        hook.run();
075                    } catch (final Throwable t) {
076                        LOGGER.error(SHUTDOWN_HOOK_MARKER, "Caught exception executing shutdown hook {}", hook, t);
077                    }
078                }
079                state.set(State.STOPPED);
080            }
081        }
082    
083        @Override
084        public Cancellable addShutdownCallback(final Runnable callback) {
085            if (isStarted()) {
086                final Cancellable receipt = new Cancellable() {
087                    // use a reference to prevent memory leaks
088                    private final Reference<Runnable> hook = new SoftReference<Runnable>(callback);
089    
090                    @Override
091                    public void cancel() {
092                        hook.clear();
093                        hooks.remove(this);
094                    }
095    
096                    @Override
097                    public void run() {
098                        final Runnable hook = this.hook.get();
099                        if (hook != null) {
100                            hook.run();
101                            this.hook.clear();
102                        }
103                    }
104    
105                    @Override
106                    public String toString() {
107                        return String.valueOf(hook.get());
108                    }
109                };
110                hooks.add(receipt);
111                return receipt;
112            }
113            throw new IllegalStateException("Cannot add new shutdown hook as this is not started. Current state: " +
114                state.get().name());
115        }
116    
117        /**
118         * Registers the shutdown thread only if this is initialized.
119         */
120        @Override
121        public void start() {
122            if (state.compareAndSet(State.INITIALIZED, State.STARTING)) {
123                try {
124                    addShutdownHook(threadFactory.newThread(this));
125                    state.set(State.STARTED);
126                } catch (final Exception e) {
127                    LOGGER.catching(e);
128                    state.set(State.STOPPED);
129                }
130            }
131        }
132    
133        private void addShutdownHook(final Thread thread) {
134            shutdownHookRef = new WeakReference<Thread>(thread);
135            Runtime.getRuntime().addShutdownHook(thread);
136        }
137    
138        /**
139         * Cancels the shutdown thread only if this is started.
140         */
141        @Override
142        public void stop() {
143            if (state.compareAndSet(State.STARTED, State.STOPPING)) {
144                try {
145                    removeShutdownHook();
146                } finally {
147                    state.set(State.STOPPED);
148                }
149            }
150        }
151    
152        private void removeShutdownHook() {
153            final Thread shutdownThread = shutdownHookRef.get();
154            if (shutdownThread != null) {
155                Runtime.getRuntime().removeShutdownHook(shutdownThread);
156                shutdownHookRef.enqueue();
157            }
158        }
159    
160        /**
161         * Indicates if this can accept shutdown hooks.
162         *
163         * @return true if this can accept shutdown hooks
164         */
165        @Override
166        public boolean isStarted() {
167            return state.get() == State.STARTED;
168        }
169    
170        @Override
171        public boolean isStopped() {
172            return state.get() == State.STOPPED;
173        }
174    
175    }