Austin Java Users GroupdeveloperWorks article –

µActor LibraryBARRY FEIGENBAUM, PH. D.02/26/13

Brief Bio

I have Ph.D. in Computer Engineering I have been developing software for more than 30 years I have worked at IBM, Amazon, Dell and others. I have worked as a developer, designer, team lead, architect and manager I have worked on business applications, operating systems, tools, web

application, etc. I have been using Java since version 1.0.2. I am Oracle certified: Java Programmer, Java Developer, Architect for Java

Technology I have written several books and articles; I have numerous US patents

Topics

Background Actor Library Design and Implementation Sample Actor Demo

Background

Moore’s Law: due to heat dissipation issues moving from faster and faster CPU speed to more copies (i.e., cores) of a CPU per processor

Most computers have multiple cores and the number is increasing over time

Automatic speed up no longer occurring; programs must become much more concurrent to exploit these cores

Traditional imperative languages do this poorly Hard to code; requires high skill Near impossible to test correct implementations Something simpler, such as the Actor Model, is needed

Background (cont)

Newer languages offering solutions Concurrency Libraries Built-in Language Facilities (ex. Actors; Functional (no side-effects)

orientation) Etc.

JRE provides support but at too low a level threads synchronized blocks java.util.concurrent

µActor Library

This presentation concentrates on a Java library for exploiting the Actor model Wikipedia: The Actor model in computer science is a mathematical model of

concurrent computation that treats "actors" as the universal primitives of concurrent digital computation: in response to a message that it receives, an actor can make local decisions, create more actors, send more messages, and determine how to respond to the next message received.

This library can be used by any Java 6+ application

http://www.ibm.com/developerworks/library/j-javaactors/index.html

µActor Library (cont)

Lightweight and easy to use Pure-Java library (no AOP, etc.) Configurable and dynamic Key Concepts (interfaces with default implementations)

Actor – unit of execution; processes 1 message at a time Message – defines an action, has from/to/subject/data/+ ActorManager – manages actors; allocates threads to actors to process

messages

Actor Runtime Model

Managers own 0+ Actors Managers manage 0+ Threads Actors buffer 0+ Messages Managers send messages to Actors Actors use Threads to process

messagesManager Actor

Message

*

*

Thread*Per

Message

ActorManager

Actor lifetime management Actor runtime lifecycle

management Message sending services DefaultActorManager

implementation Adds more API, including thread

pool management

Actor extends Runnable

Message processing and capacity Distinct identity, category Lifecycle, belongs to only one

manager AbstractActor partial

implementation Adds some more services Multiple levels of subclasses

possible

Actor Lifecycle

1. New2. Activate3. Run4. Receive (repeated)5. Deactivate6. Garbage

Activated

Run

Deactivated

Idle

ReceiveSuspended

Shutdown

New

Consumes thread in receive state

Message

Message body Sender, subject, data

Optional but typical Target supplied via send operation

Added to message by send code DefaultMessage implementation

Multiple levels of subclasses possible

Execution Model

Multiple actors, possibly of different types, cooperate by sending messages to each other.

Sends can fail - count limit exceeded, bad subject, etc.

Each actor has a queue of pending (received) messages.

When a thread is available, the manager dispatches an actor’s receive method passing in the next message.

Receive should be short lived

TestActor

A sample actor Repeats sends

count down Define lifecycle

callback methods (for illustration)

Define on start callback

public class TestActor extends TestableActor {

@Override public void activate() { super.activate(); }

@Override public void deactivate() { super.deactivate(); }

@Override protected void runBody() { DefaultMessage m = new DefaultMessage("init", 8); getManager().send(m, null, this); }

TestActor (cont)

Assume superclass has overridden receive to call loopBody

Process repeat message Repeat send N-1

times to random actor

@Overrideprotected void loopBody(Message m) { String subject = m.getSubject();

if ("repeat".equals(subject)) { int count = (Integer) m.getData(); if (count > 0) { m = new DefaultMessage("repeat", count - 1); String toName = "actor" + ???; Actor to = actorTest.getTestActors().get(toName) getManager().send(m, this, to); }

TestActor (cont)

Process init message Send count

messages to random actors with random delays

Process other messages Typically signal

error or delegate to superclass

} else if ("init".equals(subject)) { int count = (Integer) m.getData(); for (int i = 0; i < count; i++) { m = new DefaultMessage("repeat", count); String toName = "actor“ + ???; Actor to = actorTest.getTestActors().get(toName); getManager().send(m, this, to); DefaultMessage dm = new DefaultMessage("repeat", count); dm.setDelayUntil(new Date().getTime() + ???); getManager().send(dm, this, this.getClass().getSimpleName()); } } else { … }}

Example Main

Access an actor manager Create some actors in the

common category Create some actors in the

default category Start all the actors Keep main alive to allow

actors to run Terminate actor processing

DefaultActorManager am = DefaultActorManager.getDefaultInstance(); : Map<String, Actor> testActors = new HashMap<String, Actor>(); for (int i = 0; i < 2; i++) { Actor a = am.createActor(TestActor.class, "common" + i); a.setCategory("common"); testActors.put(a.getName(), a); } for (int i = 0; i < 5; i++) { Actor a = am.createActor(TestActor.class, "actor" + i); testActors.put(a.getName(), a); } for (String key : testActors.keySet()) { am.startActor(testActors.get(key)); } for (int i = 120; i > 0; i--) { if (i < 10 || i % 10 == 0) System.out.printf("main waiting: %d...%n", i); delay(1000);}:am.terminateAndWait();

Visualize running Actors

GUI shows any activity Controls at top select example and

control execution Green bar shows active threads Circle shows active actors and

messages between them Small squares show active threads Lines show messages

Bottom circles show recent history Right pane show log trace

Demo

No Example Selected Countdown started Most Busy Staring to slow down Slowing more Near done Done

Online Video of Demo

http://www.youtube.com/watch?feature=player_embedded&v=1emMgwyI9Xk

Questions