code: public final V invoke() {
          int s;
          if ((s = doInvoke() & DONE_MASK) != NORMAL)
              reportException(s);
          return getRawResult();
      }
docs: Commences performing this task, awaits its completion if
  necessary, and returns its result, or throws an (unchecked)
  {@code RuntimeException} or {@code Error} if the underlying
  computation did so.
  
  @return the computed result