1/*
2 * Copyright (C) 2011 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.base;
18
19import com.google.common.annotations.Beta;
20import com.google.common.annotations.GwtCompatible;
21
22/**
23 * A time source; returns a time value representing the number of nanoseconds
24 * elapsed since some fixed but arbitrary point in time.
25 *
26 * @author Kevin Bourrillion
27 * @since 10.0
28 *     (<a href="http://code.google.com/p/guava-libraries/wiki/Compatibility"
29 *     >mostly source-compatible</a> since 9.0)
30 */
31@Beta
32@GwtCompatible
33public abstract class Ticker {
34  /**
35   * Constructor for use by subclasses.
36   */
37  protected Ticker() {}
38
39  /**
40   * Returns the number of nanoseconds elapsed since this ticker's fixed
41   * point of reference.
42   */
43  public abstract long read();
44
45  /**
46   * A ticker that reads the current time using {@link System#nanoTime}.
47   *
48   * @since 10.0
49   */
50  public static Ticker systemTicker() {
51    return SYSTEM_TICKER;
52  }
53
54  private static final Ticker SYSTEM_TICKER = new Ticker() {
55    @Override
56    public long read() {
57      return Platform.systemNanoTime();
58    }
59  };
60}
61