How to correctly limit bandwith usage with Java netty?

Question

For a download client that I developed in Java using the netty nio lib I also implemented a bandwith limitation feature. Technically I do so via a GlobalTrafficShapingHandler object. Based on this class' JavaDoc I initialize the nio client pipeline as follows:

...
trafficHandler = new GlobalTrafficShapingHandler(
        new HashedWheelTimer(), 0, 0, 1000);
execHandler = new ExecutionHandler(
        new OrderedMemoryAwareThreadPoolExecutor(20, 0, 0));
...

public ChannelPipeline getPipeline() throws Exception
{
    // create default pipeline
    ChannelPipeline pipeline = pipeline(); 

    // traffic shaping handler
    pipeline.addLast("global-traffic-shaping", trafficHandler);

    // SSL support
    if(useSSL)
    {
        SSLEngine sslEngine = createSSLEngine();
        pipeline.addLast("ssl", new SslHandler(sslEngine));
    }

    // memory executor
    pipeline.addLast("memory-executor", execHandler);

    // business logic
    pipeline.addLast("data-processing", 
        new NettyNioClientHandler(
            nettyNioClient, localer, logger, ncMgr, username, useSSL));

    return pipeline;
}

And during runtime I then set the max. download speed via

public void setDlSpeedLimit(long limit)
{
    if(limit < 0)
        return;

    trafficHandler.configure(0, limit * 1000L);
}

Ok, so basically the netty nio functionality works fine and fast. When I set the max. download speed in the application, I can also see that the bandwidth usage is indeed capped at a max. level. I monitor the bandwith usage via

trafficHandler.getTrafficCounter().getLastReadThroughput();

However, unfortunately the max. speed I monitor is not to what I have set it before, not even close. For example, I originally (w/o limit) have a download speed of about 2000 kb/s, then I set the limit to 300 kb/s as described above, but the real download speed is then varying from 700-900 kb/s.

So my problem in this case is: I can see that the traffic shaper is doing something, but not as I wanted it to. Do I miss something here, any step in the pipeline initialization for example?

Thanks in advance for your help!

Answer 1

Ok, so it seems there are not other ideas.
The only thing that helped me a bit was to increase the timing counter to 5-10 sec.

Cheers!

Answer 2

Your getPipeline() is instantiating GlobalTrafficShapingHandler every time a new pipeline is requested. You should only instantiate one and reuse it in all pipelines instead. This is also true for other classes, such as HashedWheelTimer.

Netty has quite a few classes that must be shared among pipelines. Usually the documentation clearly mentions this. You should examine each classes' javadoc and make sure you are following them.