JMH Internal Performance Testing

Java micro benchmark harness, herein annotated as JMH. Is a micro benchmarking tool meant for internal performance testing. It looks similar to JUnit and a respective unit test. But it's intent is to benchmark the performance of a method, generally without calling to an external service.

class BenchmarkLists {
  @Benchmark 
  fun benchmark_comprehension() : List<Int> {
    return (1..2).map { it  + 5 }
  }
}

The benchmark annotation, is the equivalent of a @Test method. It executes as a benchmark, how it runs is dependent on the configuration.

Setup & Teardown

Like Junit with @Before there are methods to setup and configure a benchmark run. The common use case for this is to instaniate core data connections, load a file or some other configuration.

As an example, in testing a serializer, rather than performing file IO in each respective benchmark method it should be loaded before each run. Code called during the @Setup will not be considered in the final benchmark results.

class BenchmarkLists {
  lateinit var rawJson :String

  @Setup
  fun setup() {
    rawJson = File.read("/tmp/data.json").readText()
  }

  @Teardown 
  fun teardown() {
    // Close file or connections.
  }

  @Benchmark 
  fun benchmark_comprehension() : List<Int> {
    return (1..2).map { it  + 5 }
  }
}

With kotlin you can set up properties via lateinit var, and then have them set via the @Setup method.

Parameters

Each JMH benchmark has the idea of a set of parameters. These parameters allow for benchmarking, or testing performance across several different variables. A use case would be to test several files of varying size.

Gradle Plugins

Kotlinx

• Source

I've not had much luck with this version, and have opted for the below.

JMH Gradle Plugin

• Source

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