code: public boolean tryUnfork() {
      Thread t;
      return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
          ? ((ForkJoinWorkerThread) t).workQueue.tryUnpush(this)
          : ForkJoinPool.common.tryExternalUnpush(this));
    }
docs: Tries to unschedule this task for execution. This method will typically (but is not guaranteed
  to) succeed if this task is the most recently forked task by the current thread, and has not
  commenced executing in another thread. This method may be useful when arranging alternative
  local processing of tasks that could have been, but were not, stolen.
  
  @return {@code true} if unforked