int count = 1;
        final ExecutorService executorService = Executors.newFixedThreadPool(options.numOfThreads);
        try {
            while (count != 0) {
                count = ComponentUtil.getThumbnailManager().generate(executorService, options.cleanup);
                totalCount += count;
            }
            executorService.shutdown();
            executorService.awaitTermination(60, TimeUnit.SECONDS);

    protected Boolean available = null;

    /**
     * Registers this thumbnail generator with the thumbnail manager.
     */
    public void register() {
        ComponentUtil.getThumbnailManager().add(this);
    }

    /**
     * Default constructor for BaseThumbnailGenerator.
     */
    public BaseThumbnailGenerator() {
        // Default constructor
    }

    /**

        }
        try {
            if (fessConfig.isThumbnailCrawlerEnabled()) {
                final ThumbnailManager thumbnailManager = ComponentUtil.getThumbnailManager();
                final String thumbnailField = fessConfig.getIndexFieldThumbnail();
                docList.stream().forEach(doc -> {
                    if (!thumbnailManager.offer(doc)) {

                cmdList.add("-Dpdfbox.fontcache=" + ownTmpDir.getAbsolutePath());
            } else {
                ownTmpDir = null;
            }
        }

        cmdList.add(ComponentUtil.getThumbnailManager().getThumbnailPathOption());

        if (!jvmOptions.isEmpty()) {
            jvmOptions.stream().filter(StringUtil::isNotBlank).forEach(cmdList::add);
        }