setHead(tmp.isZero() ? headSentinel(arity) : tmp);
head = (tmp.isZero() ? headSentinel(arity) : tmp);
  private final boolean popOverflow(int arity) throws VM_PragmaNoInline {    do {      if (head.NE(headSentinel(arity)))	queue.free(bufferStart(head));      VM_Address tmp = queue.dequeue(arity);      setHead(tmp.isZero() ? headSentinel(arity) : tmp);    } while (bufferOffset(head) == 0);    if (head.EQ(headSentinel(arity)))      return consumerStarved(arity);    else       return true;  }