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 * 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 CachedClock instance = new CachedClock();
32 private volatile long millis = System.currentTimeMillis();
33 private volatile short count = 0;
34 private final Thread updater = new Thread("Clock Updater Thread") {
35 public void run() {
36 while (true) {
37 long time = System.currentTimeMillis();
38 millis = time;
39 Util.getUnsafe().park(true, time + 1); // abs (millis)
40 // Util.getUnsafe().park(false, 1000 * 1000);// relative(nanos)
41 }
42 }
43 };
44
45 private CachedClock() {
46 updater.setDaemon(true);
47 updater.start();
48 }
49
50 public static CachedClock 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. Timers on most platforms do not
57 * have millisecond granularity, the returned value may "jump" every 10 or
58 * 16 milliseconds. To reduce this problem, this method also updates the
59 * internal time value every 1024 calls.
60 * @return the cached time
61 */
62 @Override
63 public long currentTimeMillis() {
64
65 // improve granularity: also update time field every 1024 calls.
66 // (the bit fiddling means we don't need to worry about overflows)
67 if ((++count & UPDATE_THRESHOLD) == UPDATE_THRESHOLD) {
68 millis = System.currentTimeMillis();
69 }
70 return millis;
71 }
72 }