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    package org.apache.logging.log4j.core.config;
018    
019    import java.io.File;
020    import java.util.List;
021    import java.util.concurrent.atomic.AtomicInteger;
022    import java.util.concurrent.locks.Lock;
023    import java.util.concurrent.locks.ReentrantLock;
024    
025    /**
026     * Configuration monitor that periodically checks the timestamp of the configuration file and calls the
027     * ConfigurationListeners when an update occurs.
028     */
029    public class FileConfigurationMonitor implements ConfigurationMonitor {
030    
031        private static final int MASK = 0x0f;
032    
033        private static final int MIN_INTERVAL = 5;
034    
035        private static final int MILLIS_PER_SECOND = 1000;
036    
037        private final File file;
038    
039        private long lastModified;
040    
041        private final List<ConfigurationListener> listeners;
042    
043        private final int intervalSeconds;
044    
045        private long nextCheck;
046    
047        private final AtomicInteger counter = new AtomicInteger(0);
048    
049        private static final Lock LOCK = new ReentrantLock();
050    
051        private final Reconfigurable reconfigurable;
052    
053        /**
054         * Constructor.
055         * @param reconfigurable The Configuration that can be reconfigured.
056         * @param file The File to monitor.
057         * @param listeners The List of ConfigurationListeners to notify upon a change.
058         * @param intervalSeconds The monitor interval in seconds. The minimum interval is 5 seconds.
059         */
060        public FileConfigurationMonitor(final Reconfigurable reconfigurable, final File file,
061                                        final List<ConfigurationListener> listeners,
062                                        final int intervalSeconds) {
063            this.reconfigurable = reconfigurable;
064            this.file = file;
065            this.lastModified = file.lastModified();
066            this.listeners = listeners;
067            this.intervalSeconds = (intervalSeconds < MIN_INTERVAL ? MIN_INTERVAL : intervalSeconds) * MILLIS_PER_SECOND;
068            this.nextCheck = System.currentTimeMillis() + intervalSeconds;
069        }
070    
071        /**
072         * Called to determine if the configuration has changed.
073         */
074        @Override
075        public void checkConfiguration() {
076            final long current = System.currentTimeMillis();
077            if (((counter.incrementAndGet() & MASK) == 0) && (current >= nextCheck)) {
078                LOCK.lock();
079                try {
080                    nextCheck = current + intervalSeconds;
081                    if (file.lastModified() > lastModified) {
082                        lastModified = file.lastModified();
083                        for (final ConfigurationListener listener : listeners) {
084                            final Thread thread = new Thread(new ReconfigurationWorker(listener, reconfigurable));
085                            thread.setDaemon(true);
086                            thread.start();
087                        }
088                    }
089                } finally {
090                    LOCK.unlock();
091                }
092            }
093        }
094    
095        private class ReconfigurationWorker implements Runnable {
096    
097            private final ConfigurationListener listener;
098            private final Reconfigurable reconfigurable;
099    
100            public ReconfigurationWorker(final ConfigurationListener listener, final Reconfigurable reconfigurable) {
101                this.listener = listener;
102                this.reconfigurable = reconfigurable;
103            }
104    
105            @Override
106            public void run() {
107                listener.onChange(reconfigurable);
108            }
109        }
110    }