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/*
 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */
package org.openjdk.jmh.samples;

import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

import java.util.concurrent.TimeUnit;

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Thread)
public class JMHSample_09_Blackholes {

    /*
     * Should you need returning multiple results, you have to consider two options.
     *
     * NOTE: If you are only producing a single result, it is more readable to use
     * the implicit return, as in org.openjdk.jmh.samples.JMHSample_08_DeadCode.
     * Do not make your benchmark code less readable with explicit Blackholes!
     */

    double x1 = Math.PI;
    double x2 = Math.PI * 2;

    /*
     * Baseline measurement: how much single Math.log costs.
     */

    @Benchmark
    public double baseline() {
        return Math.log(x1);
    }

    /*
     * While the Math.log(x2) computation is intact, Math.log(x1)
     * is redundant and optimized out.
     */

    @Benchmark
    public double measureWrong() {
        Math.log(x1);
        return Math.log(x2);
    }

    /*
     * This demonstrates Option A:
     *
     * Merge multiple results into one and return it.
     * This is OK when is computation is relatively heavyweight, and merging
     * the results does not offset the results much.
     */

    @Benchmark
    public double measureRight_1() {
        return Math.log(x1) + Math.log(x2);
    }

    /*
     * This demonstrates Option B:
     *
     * Use explicit Blackhole objects, and sink the values there.
     * (Background: Blackhole is just another @State object, bundled with JMH).
     */

    @Benchmark
    public void measureRight_2(Blackhole bh) {
        bh.consume(Math.log(x1));
        bh.consume(Math.log(x2));
    }

    /*
     * ============================== HOW TO RUN THIS TEST: ====================================
     *
     * You will see measureWrong() running on-par with baseline().
     * Both measureRight() are measuring twice the baseline, so the logs are intact.
     *
     * You can run this test:
     *
     * a) Via the command line:
     *    $ mvn clean install
     *    $ java -jar target/benchmarks.jar ".*JMHSample_09.*" -wi 5 -i 5 -f 1
     *    (we requested 5 warmup/measurement iterations, single fork)
     *
     * b) Via the Java API:
     *    (see the JMH homepage for possible caveats when running from IDE:
     *      http://openjdk.java.net/projects/code-tools/jmh/)
     */

    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(".*" + JMHSample_09_Blackholes.class.getSimpleName() + ".*")
                .warmupIterations(5)
                .measurementIterations(5)
                .forks(1)
                .build();

        new Runner(opt).run();
    }


}