code: protected static ForkJoinTask<?> peekNextLocalTask() {
      Thread t;
      ForkJoinPool.WorkQueue q;
      if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
        q = ((ForkJoinWorkerThread) t).workQueue;
      else
        q = ForkJoinPool.commonSubmitterQueue();
      return (q == null) ? null : q.peek();
    }
docs: Returns, but does not unschedule or execute, a task queued by the current thread but not yet
  executed, if one is immediately available. There is no guarantee that this task will actually
  be polled or executed next. Conversely, this method may return null even if a task exists but
  cannot be accessed without contention with other threads. This method is designed primarily to
  support extensions, and is unlikely to be useful otherwise.
  
  @return the next task, or {@code null} if none are available