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 {