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Copyright Tristan Aubrey-Jones May 2008.
Abstract: A project investigating and developing an implicitly concurrent programming language, based on a metaphor taken from the physical world is reported. Uses a programming paradigm where programs consist of systems of autonomous agents, or active objects which communicate via message passing. A language enhancing Java with actors and linear types is presented. Example programs are written, compiled, and executed to evaluate the usefulness of the language. The language found to provide a familiar notation for implicit parallelism, and a compelling new model for concurrency, combining the performance of shared variables with the elegance of message passing.
Introductory Slides (PDF),
Report (PDF),
ActiveJava compiler prototype (ajavac),
ActiveJava runtime library (ajava_lang).
Examples:
calc - pocket calculator actor program
dining - dining philosophers actor program (never deadlocks)
sort - parallel quicksort implementation ("SortBenchmark" sorts 10,000 random integers using actors, java threads, and sequentially and compares)
To compile examples use:compile.bat ./calc compile.bat ./sort compile.bat ./diningTo run examples use:
run ./calc Main run ./dining Main run ./dining Main fast run ./sort Main run ./sort SortingBenchmark
import java.util.Random;
import org.taj.ajava.lang.*;
public class Philosopher extends Actor
{
private int id;
private Table table;
private Fork lhf, rhf;
private int state;
public Philosopher(Table table, int id)
{
this.table = table;
this.id = id;
this.state = State.THINKING;
printStatus("thinking");
randomDelay();
}
private void think()
{
table.deliver(new MoveForks(id, lhf, rhf));
state = State.THINKING;
randomDelay();
printStatus("thinking");
}
public static class IsHungry
{
public int id;
public IsHungry(int id)
{
this.id = id;
}
}
private void hungry()
{
state = State.HUNGRY;
printStatus("hungry");
table.deliver(new IsHungry(id));
}
private void react_0(MoveForks frks)
{
this.lhf = frks.lhf;
this.rhf = frks.rhf;
eat();
}
public void deliver(MoveForks frks)
{
bufferMessage(new org.taj.ajava.runtime.ActorMessage(frks, 0));
}
protected void react(MoveForks frks)
{
react_0(frks);
}
private void eat()
{
state = State.EATING;
randomDelay();
printStatus("eating with fork " + Integer.toString(lhf.getId()) + " and " + Integer.toString(rhf.getId()));
}
private void printStatus(String status)
{
Stdout.getInstance().deliver("Philosopher " + Integer.toString(id) + " is " + status + "\n");
}
private static final Random RNG = new Random();
private int countdown;
private void randomDelay()
{
countdown = RNG.nextInt(10) + 1;
}
private void react_1(Clock.Tick t)
{
countdown--;
if (countdown == 0) proceed();
}
public void deliver(Clock.Tick t)
{
bufferMessage(new org.taj.ajava.runtime.ActorMessage(t, 1));
}
protected void react(Clock.Tick t)
{
react_1(t);
}
private void proceed()
{
if (state == State.THINKING) {
hungry();
}
else {
if (state == State.EATING) {
think();
}
}
}
protected void processMessage(org.taj.ajava.runtime.ActorMessage msg)
{
switch (msg.reactorId) {
case 0:
{
react_0(((MoveForks)msg.payload));
return;
}
case 1:
{
react_1(((Clock.Tick)msg.payload));
return;
}
default:
{
super.processMessage(msg);
return;
}
}
}
}