1/*
2 * Copyright (C) 2013 Google Inc.
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.caliper.runner;
18
19import static java.math.RoundingMode.CEILING;
20import static java.util.concurrent.TimeUnit.NANOSECONDS;
21
22import com.google.caliper.util.ShortDuration;
23import com.google.common.base.Ticker;
24import com.google.common.math.LongMath;
25
26/**
27 * A utility that calculates the finest granularity that can be expected from subsequent calls to
28 * {@link System#nanoTime()}.  Note that this utility necessarily invokes {@link System#nanoTime()}
29 * directly rather than using {@link Ticker} because the extra indirection might cause additional
30 * overhead.
31 */
32final class NanoTimeGranularityTester {
33  private static final int TRIALS = 1000;
34
35  ShortDuration testNanoTimeGranularity() {
36    long total = 0L;
37    for (int i = 0; i < TRIALS; i++) {
38      long first = System.nanoTime();
39      long second = System.nanoTime();
40      long third = System.nanoTime();
41      long fourth = System.nanoTime();
42      long fifth = System.nanoTime();
43      long sixth = System.nanoTime();
44      long seventh = System.nanoTime();
45      long eighth = System.nanoTime();
46      long ninth = System.nanoTime();
47      total += second - first;
48      total += third - second;
49      total += fourth - third;
50      total += fifth - fourth;
51      total += sixth - fifth;
52      total += seventh - sixth;
53      total += eighth - seventh;
54      total += ninth - eighth;
55    }
56    return ShortDuration.of(LongMath.divide(total, TRIALS * 8, CEILING), NANOSECONDS);
57  }
58}
59