Accessing JMH state

Question

I'm setting up the JMH benchmarks for my application and I'm wondering is there any difference between passing JMH state via benchmark's and accessing it from benchmark body?

In other words

@Benchmark
public int myBenchmark(MyState state) {
MyObject objFromState= state.objFromState;
return objFromState.benchmarkMe();
}

VS

@Benchmark
public int myBenchmark() {
return objFromState.benchmarkMe();
}

Answer 1

From official JMH samples:

... Since JMH is heavily used to build concurrent benchmarks, we opted for an explicit notion of state-bearing objects ... Benchmark methods can reference the states, and JMH will inject the appropriate states while calling these methods.

All samples I saw always reference a state the same way as in the snippet:

  @State(Scope.Thread)
  public static class ThreadState {
      volatile double x = Math.PI;
  }

  @Benchmark
  public void measureUnshared(ThreadState state) {
    state.x++;
  }

You have to specify the scope of your state, explicitly declare it using annotation - you "register" it by doing this. The state object further will be injected to a method refers to it (by declaring the dependency as a method parameter). In your second snippet you reference to the state object - yes, but this is not a shared state.