| /* |
| * Copyright (C) 2013 Google Inc. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.google.caliper.runner; |
| |
| import static java.math.RoundingMode.CEILING; |
| import static java.util.concurrent.TimeUnit.NANOSECONDS; |
| |
| import com.google.caliper.util.ShortDuration; |
| import com.google.common.base.Ticker; |
| import com.google.common.math.LongMath; |
| |
| /** |
| * A utility that calculates the finest granularity that can be expected from subsequent calls to |
| * {@link System#nanoTime()}. Note that this utility necessarily invokes {@link System#nanoTime()} |
| * directly rather than using {@link Ticker} because the extra indirection might cause additional |
| * overhead. |
| */ |
| final class NanoTimeGranularityTester { |
| private static final int TRIALS = 1000; |
| |
| ShortDuration testNanoTimeGranularity() { |
| long total = 0L; |
| for (int i = 0; i < TRIALS; i++) { |
| long first = System.nanoTime(); |
| long second = System.nanoTime(); |
| long third = System.nanoTime(); |
| long fourth = System.nanoTime(); |
| long fifth = System.nanoTime(); |
| long sixth = System.nanoTime(); |
| long seventh = System.nanoTime(); |
| long eighth = System.nanoTime(); |
| long ninth = System.nanoTime(); |
| total += second - first; |
| total += third - second; |
| total += fourth - third; |
| total += fifth - fourth; |
| total += sixth - fifth; |
| total += seventh - sixth; |
| total += eighth - seventh; |
| total += ninth - eighth; |
| } |
| return ShortDuration.of(LongMath.divide(total, TRIALS * 8, CEILING), NANOSECONDS); |
| } |
| } |