Jas - A legacy implementation of an actor system

A system that abstract a simplified implementation of the actor model. Originally started as a university project for a concurrent and distributed programming course, I proceeded to add some features like support for remote actors and a basic cluster system based on legacy RMI technology.

Still under development, and likely bugged, it's not recommended to try it in a real case of use.

Logical architecture

For an exhaustive explanation of the system's logical architecture please refer to pcd-actors' README, at a local level the structure remained more or less the same, except for some additions aimed to handle the distributed part of the Actor System.

The overall structure has been enveloped on a fairly basic and still without failure-detection cluster system featuring legacy java RMI, therefore it needs a rmi registry running. One of the many difference between the previous local implementation is represented by the mandatory naming of the actors, this allow the ActorSystem to track every actor inside the cluster in case of distributed computing.

Basically, after starting the cluster as a seed (can be seen as leader node) all other nodes can subsequently join by specifying the seed address; every time a new member joins the cluster, all other nodes will be update their members list and everytime an ActorSystem create an actor, either LOCAL or REMOTE all members of the cluster update their systems in order to track all actors on the cluster.

General operations

In order to start some actors it is necessary to create an actor system and get from it actor reference, used to send messages between actors.

Local

Currently there's no real distinction between local actors and remote actors, so for now it is necessary to catch RemoteException or declare it in the throws clausole. Here an example using a basic implementation of an actor:

A basic message implementation

import io.github.codepr.jas.actors.Message;

public class TrivialMessage implements Message {}

An actor that do nothing usefull on the receive, just printing who sent the message

import java.io.Serializable;
import java.rmi.RemoteException;
import io.github.codepr.jas.actors.AbsActor;

public class TrivialActor extends AbsActor<TrivialMessage> implements Serializable {
    private static final long serialVersionUID = 227L;

    @Override
    public void receive(TrivialMessage message) {
        try {
            System.out.println(" [" + self.getName() + "] Trivial message received from " + sender.getName());
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }
}

The ActorSystem running

import java.rmi.RemoteException;
import io.github.codepr.jas.actors.ActorRef;
import io.github.codepr.jas.actors.ActorSystem.ActorMode;
import io.github.codepr.jas.actors.ActorSystemImpl;

public class Main {
    public static void main(String[] args) throws Exception {
        ActorSystem system = new ActorSystemImpl();
        ActorRef ref1 = system.actorOf(TrivialActor.class, ActorMode.LOCAL, "127.0.0.1/ref1");
        ActorRef ref2 = system.actorOf(TrivialActor.class, ActorMode.LOCAL, "127.0.0.1/ref2");
        ActorRef ref5 = system.actorOf(TrivialActor.class, ActorMode.LOCAL, "127.0.0.1/ref5");
        ref1.send(new TrivialMessage(), ref2);
    }
}

Cluster Mode

The system can be distributed across a network of computers, here an example setting up a two nodes cluster:

Node 1 - IP: 10.0.0.1

import java.rmi.RemoteException;
import io.github.codepr.jas.actors.ActorRef;
import io.github.codepr.jas.actors.ActorSystem.ActorMode;
import io.github.codepr.jas.actors.ActorSystem.SystemMode;
import io.github.codepr.jas.actors.ActorSystemImpl;
import io.github.codepr.jas.actors.remote.Cluster;
import io.github.codepr.jas.actors.remote.ClusterFactory;

public class Node1 {
    public static void main(String[] args) throws Exception {
        // ActorSystemImpl takes at least 1 argument, here we start it in CLUSTER mode, setting the host as 10.0.0.1
        // and the seed host (can be seen as a leader needed to start and join the cluster) to the same address.
        // If omitted those fields default to 127.0.0.1
        Cluster cluster = ClusterFactory.joinCluster(new ActorSystemImpl(SystemMode.CLUSTER), "10.0.0.1", "10.0.0.1");
        ActorRef ref1 = cluster.actorOf(TrivialActor.class, ActorMode.LOCAL, "10.0.0.1/ref1");
        ActorRef ref2 = cluster.actorOf(TrivialActor.class, ActorMode.REMOTE, "10.0.0.1/ref2");
        ActorRef ref5 = cluster.actorOf(TrivialActor.class, ActorMode.REMOTE, "10.0.0.1/ref5");
    }
}

Node 2 - IP: 10.0.0.2

actorSelection can be used to locate remote actors inside the cluster

import java.rmi.RemoteException;
import io.github.codepr.jas.actors.ActorRef;
import io.github.codepr.jas.actors.ActorSystem.ActorMode;
import io.github.codepr.jas.actors.ActorSystem.SystemMode;
import io.github.codepr.jas.actors.ActorSystemImpl;
import io.github.codepr.jas.actors.remote.Cluster;
import io.github.codepr.jas.actors.remote.ClusterFactory;

public class Node2 {
    public static void main(String[] args) throws Exception {
        Cluster cluster = ClusterFactory.joinCluster(new ActorSystemImpl(SystemMode.CLUSTER), "10.0.0.2", "10.0.0.1");
        ActorRef ref3 = cluster.actorOf(TrivialActor.class, ActorMode.LOCAL, "10.0.0.2/ref3");
        ActorRef ref2 = cluster.actorSelection("10.0.0.1/ref2");
        ActorRef ref5 = cluster.actorSelection("10.0.0.1/ref5");
        ref3.send(new TrivialMessage(), ref2);
        ref2.send(new TrivialMessage(), ref5);
    }
}

Execution

On node1, start an RMI registry instance (can be done also using rmi script), supposing to have Node1.java and Node2.java inside the package:

$ java -cp target/classes io.github.codepr.jas.Node1

Same on node2

$ java -cp target/classes io.github.codepr.jas.Node2

Building

The jas project is configured as a Maven project. To compile it:

$ mvn clean compile

To build the actor system as a library use the following command

$ mvn package

The output library will be created by Maven inside the folder target, with name jas.jar.

To run the tests use the command

$ mvn test

TODO

• Some refactoring of bad code parts
• Better handle of the RemoteException thing, specially for local actors
• Add a RMISecurityManager
• Decouple of the remote calls from the local ones
• A basic failure detection on the cluster side of the project

License

The MIT License (MIT)

Copyright (c) 2016 Andrea Giacomo Baldan

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.