ClosedChannelException when using netty and resteasy with concurrent requests

RestNodeStarterTest.groovy

//this is the testcase
class RestNodeStarterTest {

    ResteasyDeployment deployment;

    SomeApi someApi;

    NettyJaxrsServer server;


    @Before
    public void setUp() {
        someApi = new SomeApi();

        deployment = new ResteasyDeployment();
        deployment.setResources(Arrays.asList(someApi));

        server = new NettyJaxrsServer();
        server.setDeployment(deployment);


        int port = 3000;
        server.setPort(port);
        server.start();
    }

    @Test
    //dummy test to make the server stand still
    public void testBasicFlow() throws Exception {
        //when i execute the request with curl it seems fine
        //curl --include http://127.0.0.1:3000/api/1234
        Thread.sleep(100000)

        //but when i use ab tool for more requests, i get the java.nio.channels.ClosedChannelException
        //ab -n 100 -c 1 http://127.0.0.1:3000/api/1234
    }


    @After
    public void tearDown() {
        server.stop()
    }

}

SomeApi.groovy

//this is the rest resource
@Path("/")
public class SomeApi {

    @GET
    @Path("api/{someValue}")
    public Response getSomeStuff(@PathParam("someValue") String someValue) {
        return Response.status(200).entity("Parameter is: " + someValue).build();
    }
}