code: private int doInvoke() {
          int s; Thread t; ForkJoinWorkerThread wt;
          if ((s = doExec()) >= 0) {
              if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
                  s = (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue,
                                                                    this);
              else
                  s = externalAwaitDone();
          }
          return s;
      }
docs: Implementation for invoke, quietlyInvoke.
  
  @return status upon completion