code: public void close() {
          if (closed.compareAndSet(false, true)) {
              synchronized (meterMapLock) {
                  for (Meter meter : meterMap.values()) {
                      meter.close();
                  }
              }
          }
      }
docs: Closes this registry, releasing any resources in the process. Once closed, this registry will no longer
  accept new meters and any publishing activity will cease.