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.async; 018 019 import com.lmax.disruptor.util.Util; 020 021 /** 022 * This Clock implementation is similar to CachedClock. It is slightly faster at 023 * the cost of some accuracy. 024 */ 025 public 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 public void run() { 031 while (true) { 032 long time = System.currentTimeMillis(); 033 millis = time; 034 Util.getUnsafe().park(true, time + 1); // abs (millis) 035 // Util.getUnsafe().park(false, 1000 * 1000);// relative(nanos) 036 } 037 } 038 }; 039 040 private CoarseCachedClock() { 041 updater.setDaemon(true); 042 updater.start(); 043 } 044 045 /** 046 * Returns the singleton instance. 047 * 048 * @return the singleton instance 049 */ 050 public static CoarseCachedClock instance() { 051 return instance; 052 } 053 054 /** 055 * Returns the value of a private long field that is updated by a background 056 * thread once every millisecond. Because timers on most platforms do not 057 * have millisecond granularity, the returned value may "jump" every 10 or 058 * 16 milliseconds. 059 * @return the cached time 060 */ 061 @Override 062 public long currentTimeMillis() { 063 return millis; 064 } 065 }