com.google.caliper.runner.instrument.NanoTimeGranularityModule.java Source code

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Here is the source code for com.google.caliper.runner.instrument.NanoTimeGranularityModule.java

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/*
 * 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.instrument;

import static java.math.RoundingMode.CEILING;
import static java.util.concurrent.TimeUnit.NANOSECONDS;

import com.google.caliper.runner.RunScoped;
import com.google.caliper.util.ShortDuration;
import com.google.common.base.Ticker;
import com.google.common.math.LongMath;
import dagger.Module;
import dagger.Provides;

/**
 * A module 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.
 */
@Module
public abstract class NanoTimeGranularityModule {
    private NanoTimeGranularityModule() {
    }

    private static final int TRIALS = 1000;

    @Provides
    @RunScoped
    @NanoTimeGranularity
    static 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);
    }
}