long getVisitedHierarchyCount();

    /**
     * The number of visited directories.
     */
    long getVisitedDirectoryCount();

    /**
     * The number of visited files.
     */
    long getVisitedFiles();

    /**
     * The number of files we failed to visit.
     */
    long getFailedFiles();

    @ServiceScope(Scope.Global.class)
    class Collector {