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.helpers;
18
19 import java.util.concurrent.locks.LockSupport;
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 @Override
31 public void run() {
32 while (true) {
33 final long time = System.currentTimeMillis();
34 millis = time;
35
36 // avoid explicit dependency on sun.misc.Util
37 LockSupport.parkNanos(1000 * 1000);
38 }
39 }
40 };
41
42 private CoarseCachedClock() {
43 updater.setDaemon(true);
44 updater.start();
45 }
46
47 /**
48 * Returns the singleton instance.
49 *
50 * @return the singleton instance
51 */
52 public static CoarseCachedClock instance() {
53 return instance;
54 }
55
56 /**
57 * Returns the value of a private long field that is updated by a background
58 * thread once every millisecond. Because timers on most platforms do not
59 * have millisecond granularity, the returned value may "jump" every 10 or
60 * 16 milliseconds.
61 * @return the cached time
62 */
63 @Override
64 public long currentTimeMillis() {
65 return millis;
66 }
67 }