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.util;
18
19 import java.util.concurrent.locks.LockSupport;
20
21 /**
22 * Implementation of the {@code Clock} interface that tracks the time in a
23 * private long field that is updated by a background thread once every
24 * millisecond. Timers on most platforms do not have millisecond granularity, so
25 * the returned value may "jump" every 10 or 16 milliseconds. To reduce this
26 * problem, this class also updates the internal time value every 1024 calls to
27 * {@code currentTimeMillis()}.
28 */
29 public final class CachedClock implements Clock {
30 private static final int UPDATE_THRESHOLD = 0x3FF;
31 private static final CachedClock instance = new CachedClock();
32 private volatile long millis = System.currentTimeMillis();
33 private volatile short count = 0;
34
35 private CachedClock() {
36 final Thread updater = new Thread(new Runnable() {
37 @Override
38 public void run() {
39 while (true) {
40 final long time = System.currentTimeMillis();
41 millis = time;
42
43 // avoid explicit dependency on sun.misc.Util
44 LockSupport.parkNanos(1000 * 1000);
45 }
46 }
47 }, "Clock Updater Thread");
48 updater.setDaemon(true);
49 updater.start();
50 }
51
52 public static CachedClock 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. Timers on most platforms do not
59 * have millisecond granularity, the returned value may "jump" every 10 or
60 * 16 milliseconds. To reduce this problem, this method also updates the
61 * internal time value every 1024 calls.
62 * @return the cached time
63 */
64 @Override
65 public long currentTimeMillis() {
66
67 // improve granularity: also update time field every 1024 calls.
68 // (the bit fiddling means we don't need to worry about overflows)
69 if ((++count & UPDATE_THRESHOLD) == UPDATE_THRESHOLD) {
70 millis = System.currentTimeMillis();
71 }
72 return millis;
73 }
74 }