Martin Anderson - threads v actors

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Information about Martin Anderson - threads v actors

Published on November 28, 2011

Author: bloodredsun



Slides from my lightning presentation from the London Java Community Open Conference Nov 2011


CONCURRENT SERVICE CALLS •  Most web pages need data from multiple sources •  Scatter/Gather approach to perform all the service calls in parallel then rendering the responses 2

CONCURRENCY MODEL dispatch service calls rendering controller’s job starts early done 3

THREADS•  Well understood (if not always well implemented!)•  java.util.concurrent library eases the pain•  Resource usage? 4

ACTORS•  Been around since 1973•  Erlang popularised usage•  Actor library for Java? Akka!•  Most strongly associated with Scala but has a Java API 5

USING AN EXECUTOR SERVICE IN A SERVLET public void doGet(HttpServletRequest request, HttpServletResponse response) throws…{ List<MyServiceCallable> myServiceCallables = new ArrayList<MyServiceCallable>(); for (int ii = 0; ii < 10; ii++) { myServiceCallables.add(new MyServiceCallablle(remoteClient)); } List<Future<String>> futures = executorService.invokeAll(myServiceCallables); … for (Future future : futures) { writer.write( future.get() ); } … } 6

USING AKKA ACTORS IN A SERVLET public void doGet(HttpServletRequest request, HttpServletResponse response) throws…{ Works works = new Works(); for (int ii = 0; ii < 10; ii++) { works.add(new Work())); } masterActor.tell(works); List<Future<String>> futures = works.getFutures(); … for (Future future : futures) { writer.write( future.get() ); } … } 7

SO WHAT’S IN AN ACTOR 1? public class MasterActor extends UntypedActor { private ActorRef router; static class LoadBalancer extends UntypedLoadBalancer { private final InfiniteIterator<ActorRef> workers; public LoadBalancer(ActorRef[] workers) { this.workers = new CyclicIterator<ActorRef>(asList(workers)); } public InfiniteIterator<ActorRef> seq() { return workers; } } 8

SO WHAT’S IN AN ACTOR 2? public MasterActor(final int numWorkers, final RemoteClient remoteClient) { // create an array of started workers final ActorRef[] workers = new ActorRef[numWorkers]; for (int i = 0; i < numWorkers; i++) { workers[i] = actorOf( new UntypedActorFactory() { public UntypedActor create() { return new WorkerActor(remoteClient); } }) .start(); } // wrap all the workers with a load-balancing router router = actorOf(new UntypedActorFactory() { public UntypedActor create() { return new LoadBalancer(workers); } }).start(); } 9

SO WHAT’S IN AN ACTOR 3? // message handler in MasterActor public void onReceive(Object message) { if (message instanceof Works) { for (Work work : ((Works) message).getAll()) { router.tell(work); } } } 10

SO WHAT’S IN AN ACTOR 4? public class WorkerActor extends UntypedActor { RemoteClient remoteClient; public WorkerActor(RemoteClient remoteClient) { this.remoteClient = remoteClient; } @Override public void onReceive(Object message) throws Exception { if (message instanceof Work) { Work work = (Work) message; remoteClient.execute(work); } } } 11

SO WHAT’S IN OUR REMOTECLIENT? public void execute(final Work work) throws IOException { ContentExchange exchange = new ContentExchange() { protected void onResponseComplete() throws IOException { super.onResponseComplete(); String responseContent = this.getResponseContent(); work.setFutureResponse(responseContent); } }; //set the method and the url exchange.setMethod("GET"); exchange.setURL(work.getUrl()); // start the exchange httpClient.send(exchange); } 12

SO WHY USE AKKA/ACTORS•  More resource efficient for certain jobs•  Easier for mere mortals to reason with•  Nested supervisors can restart failed actors•  Supports STM if required 13

THANK YOU Email: Twitter: @mdjanderson Blog: Betfair Blog:

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