JMH and use of Blackhole

[benjchristensen]

I was discussing JMH with @shipilev and he brought this to my attention while informing me our use of JMH may not be quite right: http://hg.openjdk.java.net/code-tools/jmh/file/48d149ac3218/jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_28_BlackholeHelpers.java

Opening this issue to track it and get our JMH input class improved: https://github.com/Netflix/RxJava/blob/master/rxjava-core/src/perf/java/rx/jmh/InputWithIncrementingInteger.java#L74

[shipilev]

This should suffice:

      dependencies {
 -        perfCompile 'org.openjdk.jmh:jmh-core:0.5.3'
 -        perfCompile 'org.openjdk.jmh:jmh-generator-annprocess:0.5.3'
 +        perfCompile 'org.openjdk.jmh:jmh-core:0.7.1'
 +        perfCompile 'org.openjdk.jmh:jmh-generator-annprocess:0.7.1'
          //perfCompile project
      }

...and:

   private CountDownLatch latch;

      @Setup
 -    public void setup() {
 +    public void setup(final BlackHole bh) {
          observable = Observable.create(new OnSubscribe<Integer>() {
              @Override
              public void call(Subscriber<? super Integer> o) {
 @@ -55,7 +55,6 @@
              }
          });

 -        final BlackHole bh = new BlackHole();
          latch = new CountDownLatch(1);

          observer = new Observer<Integer>() {

[daschl]

I know that this needs to be passed in, but is it in this case because of DCE (the hole itself would be removed rendering the other part dead too?) @shipilev

[shipilev]

Yes, Blackhole itself is DCE-d, along with the computation it consumes.

With JMH 0.6+, the attempt to instantiate Blackhole directly will throw: http://hg.openjdk.java.net/code-tools/jmh/rev/de0365d7e4d0 (see the comment there for rationale). Therefore, if there are benchmarks which fail after updating the JMH version, you know what to fix :)

[daschl]

@shipilev alright staying cool ;). Thanks!

[daschl]

@benjchristensen should I take this on?

[benjchristensen]

Thanks @shipilev for the information.

Yes @daschl If you can take this on I'd appreciate it.

[shipilev]

While you are at it, you may want to update to 0.7.2.

[benjchristensen]

Finished upgrading to 0.7.3