String fieldName,
            String sourceHint,
            String message,
            InputLocationTracker tracker) {
        StringBuilder buffer = new StringBuilder(256);
        buffer.append('\'').append(fieldName).append('\'');

        if (sourceHint != null) {
            buffer.append(" for ").append(sourceHint);
        }

        buffer.append(' ').append(message);

      if (fileOperator == null) return // Already closed.
      fileOperator = null

      var fileToClose: RandomAccessFile? = null
      synchronized(this@Relay) {
        sourceCount--
        if (sourceCount == 0) {
          fileToClose = file
          file = null
        }
      }

      fileToClose?.closeQuietly()
    }
  }

  companion object {