code: protected ForkJoinTask<?> pollSubmission() {
          WorkQueue[] ws; int wl; WorkQueue w; ForkJoinTask<?> t;
          int r = ThreadLocalRandom.nextSecondarySeed();
          if ((ws = workQueues) != null && (wl = ws.length) > 0) {
              for (int m = wl - 1, i = 0; i < wl; ++i) {
                  if ((w = ws[(i << 1) & m]) != null && (t = w.poll()) != null)
                      return t;
              }
          }
          return null;
      }
docs: Removes and returns the next unexecuted submission if one is
  available.  This method may be useful in extensions to this
  class that re-assign work in systems with multiple pools.
  
  @return the next submission, or {@code null} if none