org.openjdk.jmh.samples.JMHSample_03_States Maven / Gradle / Ivy

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 * accompanied this code).
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package org.openjdk.jmh.samples;

import org.openjdk.jmh.annotations.GenerateMicroBenchmark;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
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;

public class JMHSample_03_States {

    /*
     * Most of the time, you need to maintain some of the state while
     * the benchmark is running. Since JMH is heavily used to build
     * concurrent benchmarks, we opted to the explicit notion
     * of state-bearing objects.
     *
     * Below are two state objects. Their class names are not essential,
     * it matters they are marked with @State. These objects will be
     * instantiated on demand, and reused during the entire benchmark trial.
     *
     * The important property is that state is always instantiated by
     * one of those benchmark threads which will then have the access
     * to that state. That means you can initialize the fields as if you do
     * that in worker threads (ThreadLocals are yours, etc).
     */

    @State(Scope.Benchmark)
    public static class BenchmarkState {
        double x = Math.PI;
    }

    @State(Scope.Thread)
    public static class ThreadState {
        double x = Math.PI;
    }

    /*
     * Benchmark methods can reference the states, and JMH will inject
     * the appropriate states while calling these methods. You can have
     * no states at all, or have only one state, or have multiple states
     * referenced. This makes building multi-threaded benchmark a breeze.
     *
     * For this exercise, we have two methods.
     */

    @GenerateMicroBenchmark
    public void measureUnshared(ThreadState state) {
        // All benchmark threads will call in this method.
        //
        // However, since ThreadState is the Scope.Thread, each thread
        // will have it's own copy of the state, and this benchmark
        // will measure unshared case.
        state.x++;
    }

    @GenerateMicroBenchmark
    public void measureShared(BenchmarkState state) {
        // All benchmark threads will call in this method.
        //
        // Since BenchmarkState is the Scope.Benchmark, all threads
        // will share the state instance, and we will end up measuring
        // shared case.
        state.x++;
    }

    /*
     * ============================== HOW TO RUN THIS TEST: ====================================
     *
     * You are expected to see the drastic difference in shared and unshared cases,
     * because you either contend for single memory location, or not. This effect
     * is more articulated on large machines.
     *
     * You can run this test:
     *
     * a) Via the command line:
     *    $ mvn clean install
     *    $ java -jar target/microbenchmarks.jar ".*JMHSample_03.*" -wi 5 -i 5 -t 4 -f 1
     *    (we requested 5 measurement/warmup iterations, with 4 threads, single fork)
     *
     * b) Via the Java API:
     */

    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(".*" + JMHSample_03_States.class.getSimpleName() + ".*")
                .warmupIterations(5)
                .measurementIterations(5)
                .threads(4)
                .forks(1)
                .build();

        new Runner(opt).run();
    }

}