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 */
017package org.apache.logging.log4j.core.helpers;
018
019import java.util.concurrent.locks.LockSupport;
020
021/**
022 * This Clock implementation is similar to CachedClock. It is slightly faster at
023 * the cost of some accuracy.
024 */
025public final class CoarseCachedClock implements Clock {
026    private static CoarseCachedClock instance = new CoarseCachedClock();
027    private volatile long millis = System.currentTimeMillis();
028
029    private final Thread updater = new Thread("Clock Updater Thread") {
030        @Override
031        public void run() {
032            while (true) {
033                final long time = System.currentTimeMillis();
034                millis = time;
035
036                // avoid explicit dependency on sun.misc.Util
037                LockSupport.parkNanos(1000 * 1000);
038            }
039        }
040    };
041
042    private CoarseCachedClock() {
043        updater.setDaemon(true);
044        updater.start();
045    }
046
047    /**
048     * Returns the singleton instance.
049     *
050     * @return the singleton instance
051     */
052    public static CoarseCachedClock instance() {
053        return instance;
054    }
055
056    /**
057     * Returns the value of a private long field that is updated by a background
058     * thread once every millisecond. Because timers on most platforms do not
059     * have millisecond granularity, the returned value may "jump" every 10 or
060     * 16 milliseconds.
061     * @return the cached time
062     */
063    @Override
064    public long currentTimeMillis() {
065        return millis;
066    }
067}