How to run JMH from inside JUnit tests?

Question

I’ve been running JMH inside my existing Maven project using JUnit with no apparent ill effects. I cannot answer why the authors recommend doing things differently. I have not observed a difference in results. JMH launches a separate JVM to run benchmarks to isolate them. Here is what I do:

Add the JMH dependencies to your POM:

<dependency>
  <groupId>org.openjdk.jmh</groupId>
  <artifactId>jmh-core</artifactId>
  <version>1.21</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.openjdk.jmh</groupId>
  <artifactId>jmh-generator-annprocess</artifactId>
  <version>1.21</version>
  <scope>test</scope>
</dependency>

Note that I’ve placed them in scope test.

In Eclipse, you may need to configure the annotation processor manually. NetBeans handles this automatically.

Create your JUnit and JMH class. I’ve chosen to combine both into a single class, but that is up to you. Notice that OptionsBuilder.include is what actually determines which benchmarks will be run from your JUnit test!

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import org.junit.Test;
import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.options.*;


public class TestBenchmark 
{

      @Test public void 
    launchBenchmark() throws Exception {

            Options opt = new OptionsBuilder()
                // Specify which benchmarks to run. 
                // You can be more specific if you'd like to run only one benchmark per test.
                .include(this.getClass().getName() + ".*")
                // Set the following options as needed
                .mode (Mode.AverageTime)
                .timeUnit(TimeUnit.MICROSECONDS)
                .warmupTime(TimeValue.seconds(1))
                .warmupIterations(2)
                .measurementTime(TimeValue.seconds(1))
                .measurementIterations(2)
                .threads(2)
                .forks(1)
                .shouldFailOnError(true)
                .shouldDoGC(true)
                //.jvmArgs("-XX:+UnlockDiagnosticVMOptions", "-XX:+PrintInlining")
                //.addProfiler(WinPerfAsmProfiler.class)
                .build();

            new Runner(opt).run();
        }

    // The JMH samples are the best documentation for how to use it
    // http://hg.openjdk.java.net/code-tools/jmh/file/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/
    @State (Scope.Thread)
    public static class BenchmarkState
    {
        List<Integer> list;

          @Setup (Level.Trial) public void
        initialize() {

                Random rand = new Random();

                list = new ArrayList<>();
                for (int i = 0; i < 1000; i++)
                    list.add (rand.nextInt());
            }
    }

      @Benchmark public void 
    benchmark1 (BenchmarkState state, Blackhole bh) {

            List<Integer> list = state.list;

            for (int i = 0; i < 1000; i++)
                bh.consume (list.get (i));
        }
}

JMH’s annotation processor seems to not work well with compile-on-save in NetBeans. You may need to do a full Clean and Build whenever you modify the benchmarks. (Any suggestions appreciated!)

Run your launchBenchmark test and watch the results!

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running com.Foo
# JMH version: 1.21
# VM version: JDK 1.8.0_172, Java HotSpot(TM) 64-Bit Server VM, 25.172-b11
# VM invoker: /usr/lib/jvm/java-8-jdk/jre/bin/java
# VM options: <none>
# Warmup: 2 iterations, 1 s each
# Measurement: 2 iterations, 1 s each
# Timeout: 10 min per iteration
# Threads: 2 threads, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: com.Foo.benchmark1

# Run progress: 0.00% complete, ETA 00:00:04
# Fork: 1 of 1
# Warmup Iteration   1: 4.258 us/op
# Warmup Iteration   2: 4.359 us/op
Iteration   1: 4.121 us/op
Iteration   2: 4.029 us/op


Result "benchmark1":
  4.075 us/op


# Run complete. Total time: 00:00:06

REMEMBER: The numbers below are just data. To gain reusable insights, you need to follow up on
why the numbers are the way they are. Use profilers (see -prof, -lprof), design factorial
experiments, perform baseline and negative tests that provide experimental control, make sure
the benchmarking environment is safe on JVM/OS/HW level, ask for reviews from the domain experts.
Do not assume the numbers tell you what you want them to tell.

Benchmark                                Mode  Cnt  Score   Error  Units
Foo.benchmark1                           avgt    2  4.075          us/op
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 7.013 sec

Runner.run even returns RunResult objects on which you can do assertions, etc.

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