docs: private static String getPID() {
          String name = ManagementFactory.getRuntimeMXBean().getName();
          int index = name.indexOf('@');
          if (index == -1) {
              return null;
          }
  
          String pid = name.substring(0, index);
          if (!pid.matches("[0-9]+")) {
              return null;
          }
  
          return pid;
      }