code: private void interruptImageValidation() throws IOException {
      synchronized (imageValidatorLock) {
        if (imageValidator != null) {
          imageValidator.interrupt();
          try {
            imageValidator.join();
          } catch (InterruptedException e) {
            throw new InterruptedIOException("Standby: received interruption");
          }
        }
      }
    }
docs: Interrupts and joins ongoing image validation.
  @throws IOException