org.openjdk.jmh.samples.JMHSample_08_DeadCode Maven / Gradle / Ivy
/*
* Copyright (c) 2014, Oracle America, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of Oracle nor the names of its contributors may be used
* to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.openjdk.jmh.samples;
import org.openjdk.jmh.annotations.*;
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;
@State(Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class JMHSample_08_DeadCode {
/*
* The downfall of many benchmarks is Dead-Code Elimination (DCE): compilers
* are smart enough to deduce some computations are redundant and eliminate
* them completely. If the eliminated part was our benchmarked code, we are
* in trouble.
*
* Fortunately, JMH provides the essential infrastructure to fight this
* where appropriate: returning the result of the computation will ask JMH
* to deal with the result to limit dead-code elimination (returned results
* are implicitly consumed by Blackholes, see JMHSample_09_Blackholes).
*/
private double x = Math.PI;
@Benchmark
public void baseline() {
// do nothing, this is a baseline
}
@Benchmark
public void measureWrong() {
// This is wrong: result is not used and the entire computation is optimized away.
Math.log(x);
}
@Benchmark
public double measureRight() {
// This is correct: the result is being used.
return Math.log(x);
}
/*
* ============================== HOW TO RUN THIS TEST: ====================================
*
* You can see the unrealistically fast calculation in with measureWrong(),
* while realistic measurement with measureRight().
*
* You can run this test:
*
* a) Via the command line:
* $ mvn clean install
* $ java -jar target/benchmarks.jar JMHSample_08 -f 1
* (we requested single fork; there are also other options, see -h)
*
* 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_08_DeadCode.class.getSimpleName())
.forks(1)
.build();
new Runner(opt).run();
}
}