How to: Async Callbacks using Netty with Avro - asynchronous

Question

I'm trying to implement Asynchronous Avro calls by using its NettyServer implementation. After digging the source code, I found an example on how to use NettyServer from TestNettyServerWithCallbacks.java
When running a few test, I realize that NettyServer never calls hello(Callback) method, instead it keeps calling the synchronous hello() method. The client program prints out "Hello" but I'm expecting "Hello-ASYNC" as a result. I really have no clue what's going on.
I hope someone can shine some light on me and perhaps point out the mistake. Below are the codes I use to perform a simple asynchronous avro test.
AvroClient.java - Client code.
public class AvroClient {
public static void main(String[] args) throws InterruptedException, ExecutionException, TimeoutException {
try {
NettyTransceiver transceiver = new NettyTransceiver(new InetSocketAddress(6666));
Chat.Callback client = SpecificRequestor.getClient(Chat.Callback.class, transceiver);
final CallFuture<CharSequence> future1 = new CallFuture<CharSequence>();
client.hello(future1);
System.out.println(future1.get());
transceiver.close();
} catch (IOException ex) {
System.err.println(ex);
}
}
}
AvroNetty.java - The Server Code
public class AvroNetty {
public static void main(String[] args) {
Index indexImpl = new AsyncIndexImpl();
Chat chatImpl = new ChatImpl();
Server server = new NettyServer(new SpecificResponder(Chat.class, chatImpl), new InetSocketAddress(6666));
server.start();
System.out.println("Server is listening at port " + server.getPort());
}
}
ChatImpl.java
public class ChatImpl implements Chat.Callback {
#Override
public void hello(org.apache.avro.ipc.Callback<CharSequence> callback) throws IOException {
callback.handleResult("Hello-ASYNC");
}
#Override
public CharSequence hello() throws AvroRemoteException {
return new Utf8("Hello");
}
}
This interface is auto-generated by avro-tool
Chat.java
#SuppressWarnings("all")
public interface Chat {
public static final org.apache.avro.Protocol PROTOCOL = org.apache.avro.Protocol.parse("{\"protocol\":\"Chat\",\"namespace\":\"avro.test\",\"types\":[],\"messages\":{\"hello\":{\"request\":[],\"response\":\"string\"}}}");
java.lang.CharSequence hello() throws org.apache.avro.AvroRemoteException;
#SuppressWarnings("all")
public interface Callback extends Chat {
public static final org.apache.avro.Protocol PROTOCOL = avro.test.Chat.PROTOCOL;
void hello(org.apache.avro.ipc.Callback<java.lang.CharSequence> callback) throws java.io.IOException;
}
}
Here is the Avro Schema
{
"namespace": "avro.test",
"protocol": "Chat",
"types" : [],
"messages": {
"hello": {
"request": [],
"response": "string"
}
}
}

Answer 1

The NettyServer implementation actually doesn't implement the Async style at all. It is a deficiency in the library. Instead you need to specify an asynchronous execution handler rather than try and chain services together through callbacks. Here is what I use to setup my NettyServer to allow for this:
ExecutorService es = Executors.newCachedThreadPool();
OrderedMemoryAwareThreadPoolExecutor executor = new OrderedMemoryAwareThreadPoolExecutor(Runtime.getRuntime().availableProcessors(), 0, 0);
ExecutionHandler executionHandler = new ExecutionHandler(executor);
final NettyServer server = new NettyServer(responder, addr, new NioServerSocketChannelFactory(es, es), executionHandler);