code: public synchronized void shutdown() {
          if (zoo == null)
              return;
  
          for (int e = 0; e < zoo.length; e++) {
              if (zoo[e] == null)
                  continue;
  
              zoo[e].interrupt();
              zoo[e].shutdown();
              zoo[e] = null;
          }
          zoo = null;
  
          System.gc();
      }
docs: This method gracefully shuts down ParallelInference instance