code: @Override
      public YourFuture async(ConcurrentAsyncCall noArgLambda) {
          assertThreadCallbackNotNull(noArgLambda);
          assertExecutorServiceValid();
          if (noArgLambda.asPrimary()) { // forcing option
              return doAsyncPrimary(noArgLambda);
          } else {
              final ConcurrentAsyncImportance importance = noArgLambda.importance();
              if (importance != null) {
                  if (ConcurrentAsyncImportance.PRIMARY.equals(importance)) {
                      return doAsyncPrimary(noArgLambda);
                  } else if (ConcurrentAsyncImportance.SECONDARY.equals(importance)) {
                      return doAsyncSecondary(noArgLambda);
                  } else if (ConcurrentAsyncImportance.TERTIARY.equals(importance)) {
                      return doAsyncTertiary(noArgLambda);
                  } else { // no way
                      throw new IllegalStateException("Unknown importance: " + importance);
                  }
              } else {
                  return doAsyncSecondary(noArgLambda); // as default
              }
          }
      }
docs: ==================