code: public static Step step(String stepName)
    {
      Root root = PROFILER_STEPS.get();
      if (root != null)
      {
        Profile data = new Profile(root.nextId(), stepName);
        return new Step(root, data);
      } else
      {
        return new Step(null, null);
      }
    }
docs: Start a profiling step.
  
  @param stepName
  The name of the step.
  @return A {@code Step} object whose {@link Step#close()} method should be
  called to finish the step.