How to use JMH with gradle?

I want to use JMH, an OpenJDK microbenchmark tool, with gradle. However, Im getting the NPE on compilation. On the other hand, JMH works when using from maven.

I am not posting any build.gradle as it is basic - apply java plugin and add dependency on JHM tool (org.openjdk.jmh:jmh-core:0.2).

I have tried whats written here without success.

What else I have to do? I think something with setting the agent, but I still didnt figure it out.

Exception:

:compileJava
java.lang.NullPointerException
at org.openjdk.jmh.processor.internal.GenerateMicroBenchmarkProcessor.validMethodSignature(GenerateMicroBenchmarkProcessor.java:502)

Solution

Just finished my "masterpiece". No uber-jars, no plugins, code base separated from main & test, benchmarks compilation hooked to main, but does not run automatically in the mainstream lifecycle. Simple, explicit, and hackable, vanilla gradle.

I run it directly from IntelliJ, to run on a box you probably will need the uber-jar back :-)

Before doing it I have spent a fair amount of time trying to get that plugin work, but it's way too clunky for my taste.

Step-by-step breakdown below.

Define a new sourceSet called jmh with classpath hooked to that of the main sourceSet

sourceSets {
    jmh {
        java.srcDirs = ['src/jmh/java']
        scala.srcDirs = ['src/jmh/scala']
        resources.srcDirs = ['src/jmh/resources']
        compileClasspath += sourceSets.main.runtimeClasspath
    }
}

Define dependencies for it (at minimum JMH and its annotation processor).

dependencies {
    ...
    jmhImplementation 'org.openjdk.jmh:jmh-core:1.35'
    jmhImplementation 'org.openjdk.jmh:jmh-generator-annprocess:1.35'
}

Define a task jmh of type JavaExec

task jmh(type: JavaExec, dependsOn: jmhClasses) {
    main = 'org.openjdk.jmh.Main'
    classpath = sourceSets.jmh.compileClasspath + sourceSets.jmh.runtimeClasspath
}

Hook jmhClasses task to run after classes to make sure benchmarks are compiled with the rest of the code

classes.finalizedBy(jmhClasses)