code: private static void createThreadPool() {
          if (nprocs == -1) {
              int n = -1;
              try {
                  String env = System.getProperty("smile.threads");
                  if (env != null) {
                      n = Integer.parseInt(env);
                  }
              } catch (Exception ex) {
                  logger.error("Failed to create multi-core execution thread pool", ex);
              }
  
              if (n < 1) {
                  nprocs = Runtime.getRuntime().availableProcessors();
              } else {
                  nprocs = n;
              }
  
              if (nprocs > 1) {
                  threads = (ThreadPoolExecutor) Executors.newFixedThreadPool(nprocs, new SimpleDeamonThreadFactory());
              }
          }
      }
docs: Creates the worker thread pool.