1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache license, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the license for the specific language governing permissions and
15 * limitations under the license.
16 */
17 package org.apache.logging.log4j.core.async;
18
19 import com.lmax.disruptor.util.Util;
20
21 /**
22 * This Clock implementation is similar to CachedClock. It is slightly faster at
23 * the cost of some accuracy.
24 */
25 public final class CoarseCachedClock implements Clock {
26 private static CoarseCachedClock instance = new CoarseCachedClock();
27 private volatile long millis = System.currentTimeMillis();
28
29 private final Thread updater = new Thread("Clock Updater Thread") {
30 public void run() {
31 while (true) {
32 long time = System.currentTimeMillis();
33 millis = time;
34 Util.getUnsafe().park(true, time + 1); // abs (millis)
35 // Util.getUnsafe().park(false, 1000 * 1000);// relative(nanos)
36 }
37 }
38 };
39
40 private CoarseCachedClock() {
41 updater.setDaemon(true);
42 updater.start();
43 }
44
45 /**
46 * Returns the singleton instance.
47 *
48 * @return the singleton instance
49 */
50 public static CoarseCachedClock instance() {
51 return instance;
52 }
53
54 /**
55 * Returns the value of a private long field that is updated by a background
56 * thread once every millisecond. Because timers on most platforms do not
57 * have millisecond granularity, the returned value may "jump" every 10 or
58 * 16 milliseconds.
59 * @return the cached time
60 */
61 @Override
62 public long currentTimeMillis() {
63 return millis;
64 }
65 }