} finally {
            lock.readLock().unlock();
        }
    }

    /**
     * Get the number of active handles
     * @return the number of handles
     */
    public int getHandleCount() {
        return handles.size();
    }

    private void periodicMaintenance() {
        if (shutdown) {
            return;
        }

        lock.writeLock().lock();
        try {