@Override
    public void close(FutureCallback<Void> callback) throws IllegalStateException {
        assertOpen();

        Future<?> future = this.eventGroup.shutdownGracefully(0L, 5L, TimeUnit.SECONDS);
        future.addListener(new NetworkManagerVoidFutureCallback(callback));
    }
@ Override public void close ( FutureCallback < Void > callback ) throws IllegalStateException { assertOpen ( ) ; Future < ? > future = this . eventGroup . shutdownGracefully ( 0L , 5L , TimeUnit . SECONDS ) ; future . addListener ( new NetworkManagerVoidFutureCallback ( callback ) ) ; }
{@inheritDoc}

@throws IllegalStateException If manager is already closed.