Micro benchmarking a loop with different values in JMH

Question

It is well known that using a loop inside your JMH benchmark is not a good idea because it will be optimized by the JIT compiler and should therefore be avoided. Is there a way to feed my JMH benchmark methods with different values of int inputs (list of inputs) without using a loop.

Answer 1

Have a look at this example in the JMH documentation. You can use the @Param annotation on a field in order to tell JMH to inject the values of this annotation:

@Param({"1", "2"})
public int arg;

@Benchmark
public int doBenchmark() {
  return doSomethingWith(arg);
}

The benchmark is then run for both the values 1 and 2.

Note how, if the annotated field is not a String but a primitive, the values are parsed prior to assigment and are assigned in their converted forms. If you have multiple fields with the @Param annotation, JMH will run the benchmark with any possible permutation of the field values.

You can also overridde the value assignment when defining a JMH runner.