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}