code: public void freeTopology(String topId, Cluster cluster) {
          Set<WorkerSlot> slots = _topIdToUsedSlots.get(topId);
          if (slots == null || slots.isEmpty())
              return;
          for (WorkerSlot ws : slots) {
              cluster.freeSlot(ws);
              if (_isAlive) {
                  _freeSlots.add(ws);
              }
          }
          _topIdToUsedSlots.remove(topId);
      }
docs: Frees all the slots for a topology.
  
  @param topId   the topology to free slots for
  @param cluster the cluster to update