public synchronized void close() {
        try {
            if (fileOutputStream != null) {
                fileOutputStream.close();
                fileOutputStream = null;
            }
        } catch (IOException e) {
            throw new RuntimeException("Unable to close output stream", e);
        }
    }
@author Ulf Lilleengen
@since 5.1
Should only be used internally in the log library
vespalog/src/main/java/com/yahoo/log/FileLogTarget.java