public void activateApplication(ApplicationVersions applicationVersions, long activeSessionId) {
        ApplicationId id = applicationVersions.getId();
        try (@SuppressWarnings("unused") Lock lock = lock(id)) {
            if ( ! exists(id))
                return; // Application was deleted before activation.
            if (applicationVersions.applicationGeneration() != activeSessionId)
                return; // Application activated a new session before we got here.

            setActiveApp(applicationVersions);
            notifyConfigActivationListeners(applicationVersions);
        }
    }
Activates the config of the given app. Notifies listeners

@param applicationVersions the {@link ApplicationVersions} to be activated
configserver/src/main/java/com/yahoo/vespa/config/server/application/TenantApplications.java