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 17 package com.google.caliper.runner; 18 19 import static java.math.RoundingMode.CEILING; 20 import static java.util.concurrent.TimeUnit.NANOSECONDS; 21 22 import com.google.caliper.util.ShortDuration; 23 import com.google.common.base.Ticker; 24 import 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 */ 32 final 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
