RobotS

Robots is a pure rust actor system library, it takes a strong inspiration from erlang and akka.

Documentation can be found here.

Maintained status

I am no longer working on this crate, so features will probably not be added by me.

If you want to add features feel free to submit a PR, I will try to review it within the week.

Bugs and errors will nevertheless be corrected if an issue is opened, provided they are not too long to correct.

Build it

This library can be built on a stable rustc (starting at 1.4.0) version.

A simple

cargo build

should be enough.

Usage

Initiate the ActorSystem

In order to use this crate you first need to create an ActorSystem and give it some threads to work with.

extern crate robots;
use robots::actors::ActorSystem;

fn main() {
    let actor_system = ActorSystem::new("test".to_owned());
    actor_system.spawn_threads(1);
}

You can also shut down the actor system by calling the shutdown method on it, it will stop all threads and terminate all the actors and their allocated ressources (if you implemented their drop properly).

That's nice but you need to populate it with some Actors.

Implement an Actor

In order to define an actor you need to:

• Define a struct and have it implement the Actor trait.
• Have a function with a single argument to create it (a tuple will do that if you need multiple values, or () if you need none).

use robots::actors::{Actor, ActorCell, ActorContext};

struct Dummy;

impl Actor for Dummy {
    fn receive(&self, _message: Box<Any>, _context: ActorCell) {}
}

impl Dummy {
    fn new(_: ()) -> Dummy {
        Dummy
    }
}

Instantiate an Actor

Now let's see how to instantiate such an actor.

Actors are created with a Props, this is a structure containing a constructor for this actor and the argument for it.

There are two ways to instantiate an actor, it can either be the child of another user created actor or be the child of the root actor for user actors.

The first way looks like:

let props = Props::new(Arc::new(Dummy::new), ());
let greeter = context.actor_of(props, "dummy".to_owned());

The second looks like:

let props = Props::new(Arc::new(Dummy::new), ());
let _actor = actor_system.actor_of(props, "dummy".to_owned());

The actor_of method will give you an ActorRef to the created actor.

Note that the first way to create actors is much faster than the second one (about 10 times), so it should only be used if you want to create a new actor hierachy.

Handle messages

The actor will receive its messages in the form of Box<Any>, this allows the actor to handle multiple types of message which can be usefull in many cases (forwarding messages for example).

In order to have a concrete type from a Box<Any>, you will need to downcast it like in the following example.

impl Actor for Printer {
    fn receive(&self, message: Box<Any>, _context: ActorCell) {
        if let Ok(message) = Box::<Any>::downcast::<String>(message) {
            println!("{}", *message);
        }
    }
}

As you can see this is rather easy.

If you think that using Box<Any> is very bad and that someone should do terrible things to me, check this post before :)

ActorContext methods

Now let's see how to use the context argument.

This gives most of the communication methods and features expected of an actor:

/// Returns an ActorRef to the Actor.
fn actor_ref(&self) -> ActorRef;

/// Spawns a child actor.
fn actor_of(&self, props: Arc<ActorFactory>, name: String) -> Result<ActorRef, &'static str>;

/// Sends a Message to the targeted ActorRef.
fn tell<MessageTo: Message>(&self, to: ActorRef, message: MessageTo);

/// Creates a Future, this Future will send the message to the targetted ActorRef (and thus be
/// the sender of the message).
fn ask<MessageTo: Message>(&self, to: ActorRef, message: MessageTo, future_name: String) -> ActorRef;

/// Completes a Future.
fn complete<MessageTo: Message>(&self, to: ActorRef, complete: MessageTo);

/// Tells a future to forward its result to another Actor.
/// The Future is then dropped.
fn forward_result<T: Message>(&self, future: ActorRef, to: ActorRef);

/// Tells a future to forward its result to another Future that will be completed with this
/// result.
/// The Future is then dropped.
fn forward_result_to_future<T: Message>(&self, future: ActorRef, to: ActorRef);

/// Sends the Future a closure to apply on its value, the value will be updated with the output
/// of the closure.
fn do_computation<T: Message, F: Fn(Box<Any + Send>, ActorCell) -> T + Send + Sync + 'static>
    (&self, future: ActorRef, closure: F);

/// Requests the targeted actor to stop.
fn stop(&self, actor_ref: ActorRef);

/// Asks the father of the actor to terminate it.
fn kill_me(&self);

/// Returns an Arc to the sender of the message being handled.
fn sender(&self) -> ActorRef;

/// Father of the actor.
fn father(&self) -> ActorRef;

/// Children of the actor.
fn children(&self) -> HashMap<Arc<ActorPath>, ActorRef>;

/// Lifecycle monitoring, list of monitored actors.
fn monitoring(&self) -> HashMap<Arc<ActorPath>, (ActorRef, FailureHandler)>;

/// Actors monitoring this actor.
fn monitored_by(&self) -> Vec<ActorRef>;

/// Monitor an actor with the given handler.
fn monitor(&self, actor: ActorRef, handler: FailureHandler);

/// Logical path to the actor, such as `/user/foo/bar/baz`
fn path(&self) -> Arc<ActorPath>;

/// Future containing an Option<ActorRef> with an ActtorRef to the Actor with the given logical
/// path.
///
/// The future will have the path: `$actor/$name_request`
fn identify_actor(&self, logical_path: String, request_name: String) -> ActorRef;

/// Sends a control message to the given actor.
fn tell_control(&self, actor: ActorRef, message: ControlMessage);

/// Puts the actor in a state of failure with the given reason.
fn fail(&self, reason: &'static str);

Logging

RobotS logs informations on the info channel of the log crate.

If you have never used this crate you can simply activate the logs by adding the following lines to your executable:

extern crate env_logger;

// Your use and extern crates...

fn main() {
    env_logger::init().unwrap();

    // Your main code.
}

You will need to set the RUST_LOG environment variable to robots=info. For example when launching the factorial example we see:

➜  RobotS git:(master) ✗ RUST_LOG=robots=info cargo run --example=factorial
   Compiling RobotS v0.3.0 (file:///home/gamazeps/dev/RobotS)
     Running `target/debug/examples/factorial`
INFO:robots::actors::actor_system: Created cthulhu
INFO:robots::actors::actor_ref: /user receiving a system message
INFO:robots::actors::actor_system: Created /user actor
INFO:robots::actors::actor_ref: /system receiving a system message
INFO:robots::actors::actor_system: Created /system actor
INFO:robots::actors::actor_system: Launched the first thread
INFO:robots::actors::actor_system: Created the channel to get an ActorRef from a root actor
INFO:robots::actors::actor_ref: / is sending a message to /system
INFO:robots::actors::actor_ref: /system receiving a message
INFO:robots::actors::actor_ref: /user handling a message
INFO:robots::actors::actor_ref: /system handling a message
INFO:robots::actors::actor_ref: /system handling a message
INFO:robots::actors::actor_cell: creating actor /system/name_resolver
INFO:robots::actors::actor_ref: /system/name_resolver receiving a system message
INFO:robots::actors::actor_system: Created the /system/name_resolver actor
INFO:robots::actors::actor_ref: /system/name_resolver handling a message
INFO:robots::actors::actor_system: Created the channel to get an ActorRef from a root actor
INFO:robots::actors::actor_ref: / is sending a message to /user
INFO:robots::actors::actor_ref: /user receiving a message
INFO:robots::actors::actor_ref: /user handling a message
INFO:robots::actors::actor_cell: creating actor /user/sender
INFO:robots::actors::actor_ref: /user/sender receiving a system message
INFO:robots::actors::actor_ref: /system/name_resolver receiving a message
INFO:robots::actors::actor_ref: /user/sender handling a message
INFO:robots::actors::actor_system: Created the channel to get an ActorRef from a root actor
INFO:robots::actors::actor_ref: /system/name_resolver handling a message
INFO:robots::actors::actor_ref: / is sending a message to /user
INFO:robots::actors::actor_ref: /user receiving a message
....

This is a bit verbose but allows you to monitor the proper execution of your program.

Contributing

All contribution are welcome, if you have a feature request don't hesitate to open an issue !

Features

• Actor communication in a local context.
• Actor supervision with an actor hierarchy (each actor supervises its children).
• Failure handling with explicit reaosns and handlers.
• Ask pattern using Futures for asynchronous requests.
• Name resolving (obtaining an ActorRef from a logical path).
• Logging.

TODO

• Network communication in a transparent manner.
• Investigate the performances to shave some microseconds.
• Your crazy ideas ?

Benches

Some crude benchs were written for actor creation and local message passing.

Here are the result on my Intel(R) Core(TM) i5-3317U CPU @ 1.70GHz

test create_1000_actors                   ... bench:   3,341,549 ns/iter (+/- 173,594)
test send_1000_messages                   ... bench:   1,217,572 ns/iter (+/- 196,141)

Nevertheless, I have not yet managed to get akka working on my computer so I don't have anything to bench against so do what you want with these benches.