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//! Management for actor services and message routing. //! //! An actor is a long-lived thread that performs a specific function or set of functions and //! consumes a channel of requests from other threads using protocols to describe how and on what //! data those functions should be performed. //! //! While the actor model has numerous benefits, exherting control over actors (such as during a //! shutdown event) and keeping track of all of their channels can be challenging. This module //! provides facilities that support the use of the actor model by addressing those challenges. //! //! To maintain a registry of actors, keep track of their channels, and respond to control events, //! a special type of actor called a router is launched. A [Router][Router] encapsulates the //! channels through which clients interact with the router and the actors it maintains. The //! router's registry maps an ID for each actor to an [Actor][Actor] type similar to `Router` which //! encapsulates the channels through which actors receive their input. //! //! Actors are spawned through a control message to the router. They are provided an //! [ActorContext][ActorContext] that provides the channels over which the function receives its //! inputs and control messages, and a channel over which it can communicate its status back to the //! router. //! //! An actor function must: //! - Use the `select!` macro that is re-exported from `crossbeam_channel` to receive from both the //! request channel and the control channel. //! - Convert the `Any + Send` trait objects it receives over the request channel into the correct //! concrete type. //! - Respond to [ActorCtl::Stop][ActorCtl] messages it receives over the control channel by //! promptly stablizing its state, sending the router an [ActorStatus::Stopped][ActorStatus] status //! message, and exiting. //! //! # Simple Example //! ```no_run //! #[macro_use] //! extern crate herbert; //! use herbert::prelude::*; //! //! fn main() { //! // Create a router. This is manditory. //! let router = Router::run("example"); //! //! // Spawn an actor, here named "herbert". //! spawn_actor!(router, "herbert", |ctx: ActorContext| { //! loop { //! select! { //! // Normal message channel. //! recv(ctx.req) -> msg => { //! match msg { //! Ok(any) => { //! // Convert trait object into concrete type. //! if let Some(value) = any.downcast_ref::<String>() { //! // Do some work. //! println!("received order: {}", value); //! } else { //! // Bad value, here we're just ignoring it. //! } //! } //! Err(e) => { //! // Error receiving a normal message, choosing to terminate. //! break; //! } //! } //! } //! // Control message channel. //! recv(ctx.ctl) -> msg => { //! match msg { //! Ok(ActorCtl::Stop) => { //! // We have been requested to stop. //! // Stabilize any state and then break the loop to exit. //! break; //! } //! Err(e) => { //! // Error receiving a control message, choosing to terminate. //! break; //! }, //! } //! } //! } //! } //! // Notify the router we are stopped as our last action. //! ctx.report_stopped().unwrap(); //! }).unwrap(); //! //! // Send our order to the "herbert" actor thread. //! send_actor!(router, "herbert", String::from("2 gorditas")).unwrap(); //! //! // ... //! //! // Shut down the router. //! router.shutdown(); //! } //! ``` //! //! [Router]: struct.Router.html //! [Actor]: struct.Actor.html //! [ActorCtl]: enum.ActorCtl.html //! [ActorContext]: struct.ActorContext.html //! [ActorStatus]: enum.ActorStatus.html use std::any::Any; use std::collections::HashMap; use std::fmt; use std::panic::{catch_unwind, UnwindSafe}; use std::thread; #[macro_use] extern crate log; #[macro_use(select)] extern crate crossbeam_channel; use crossbeam_channel::{unbounded, Receiver, Sender}; pub mod prelude { //! The things you'll need. //! //! Re-exports several items from //! [crossbeam_channel](https://crates.io/crates/crossbeam-channel), including the `unbounded` //! channel type, the `Receiver` and `Sender` types, and the `select!` macro. pub use crate::{ActorContext, ActorCtl, ActorStatus, Router, RouterCtl, RouterRequest}; pub use crossbeam_channel::{select, unbounded, Receiver, Sender}; } /// The type signature of the messages that are consumed by actors. /// /// In order to support heterogenous message values between actors, a message is expressed as a /// trait object statisfying the `Any` and `Send` traits. The value is wrapped in a `Box` so the /// compiler can reason about its size. /// /// An actor must downcast the trait object back into a concrete type using the `downcast_ref` /// method of the `Any` trait. pub type Message = Box<dyn Any + Send>; /// A custom result type. pub type Result<T> = std::result::Result<T, Error>; /// A handle to the actor management thread. /// /// When a `Router` is created and its thread is spawned, channels are created to allow clients to /// send messages to the router and to the actors it is managing. Those channels are packaged into /// the `Router` struct and returned to the client. pub struct Router { pub id: String, pub req: Sender<RouterRequest>, pub ctl: Sender<RouterCtl>, handle: thread::JoinHandle<()>, } impl Router { /// Spawn the router thread and return a `Router` handle. /// /// The router thread will remain resident, consuming the channels over which requests to route /// messages to actor and control messages to manage the router itself are sent. It will also /// consume an internal channel of status messages sent back from actor threads, so it can /// perform tasks when events like the stoppage or panic of an actor thread occurs. pub fn run(id: &str) -> Self { let router_id = id.to_owned(); let (req_tx, req) = unbounded::<RouterRequest>(); let (ctl_tx, ctl) = unbounded::<RouterCtl>(); let (router_req, router_ctl) = (req_tx.clone(), ctl_tx.clone()); let handle = thread::spawn(move || { let mut table: HashMap<String, Actor> = HashMap::new(); let (stat_tx, stat) = unbounded::<ActorStatus>(); debug!("router::{}: started", router_id); loop { select! { recv(req) -> msg => { match msg { Ok(request) => { if let Some(actor) = table.get(&request.id) { actor.req.send(request.val).unwrap(); } else { error!("router::{}: actor '{}' not found", router_id, request.id); } } Err(e) => error!("router::{}: error receiving request: {}", router_id, e) } }, recv(ctl) -> msg => { match msg { Ok(RouterCtl::Spawn { id, f, resp }) => { debug!("router::{}: spawning actor '{}'", router_id, id); let (actor_req_tx, actor_req_rx) = unbounded(); let (actor_ctl_tx, actor_ctl_rx) = unbounded(); let ctx = ActorContext::new( id.clone(), actor_req_rx, actor_ctl_rx, router_req.clone(), router_ctl.clone(), stat_tx.clone() ); let panic_stat_tx = stat_tx.clone(); let actor_id = id.clone(); let handle = thread::spawn(move || { let actor_status = catch_unwind(move || { f(ctx); }); if let Err(_) = actor_status { panic_stat_tx.send(ActorStatus::Paniced(actor_id)).unwrap(); } }); table.insert(id.clone(), Actor { id: id, req: actor_req_tx, ctl: actor_ctl_tx, handle: handle, }); resp.send(()).unwrap(); }, Ok(RouterCtl::Get { id, resp }) => { if let Some(actor) = table.get(&id) { resp.send(Ok(actor.req.clone())).unwrap(); } else { resp.send(Err(Error::NoSuchActor(id.clone()))).unwrap(); } } Ok(RouterCtl::Has { id, resp }) => { resp.send(table.contains_key(&id)).unwrap(); } Ok(RouterCtl::StopActor { id, resp }) => { if let Some(actor) = table.remove(&id) { debug!("router::{}: stopping actor '{}'", router_id, actor.id); actor.ctl.send(ActorCtl::Stop).unwrap(); actor.handle.join().unwrap(); resp.send(()).unwrap(); } } Ok(RouterCtl::StopActorAsync(id)) => { if let Some(actor) = table.remove(&id) { debug!("router::{}: stopping actor '{}'", router_id, actor.id); actor.ctl.send(ActorCtl::Stop).unwrap(); } } Ok(RouterCtl::Shutdown) => { debug!("router::{}: stopping all actors ...", router_id); for (_, actor) in table.drain() { debug!("router::{}: stopping actor '{}'", router_id, actor.id); actor.ctl.send(ActorCtl::Stop).unwrap(); actor.handle.join().unwrap(); } break; } Err(e) => error!("router::{}: error receiving on ctrl: {}", router_id, e), } }, recv(stat) -> msg => { match msg { Ok(ActorStatus::Stopped(id)) => { debug!("router::{}: actor '{}' stopped", router_id, id); table.remove(&id); } Ok(ActorStatus::Paniced(id)) => { warn!("router::{}: actor '{}' paniced", router_id, id); table.remove(&id); } Err(e) => error!("router::{}: error receiving actor status: {}", router_id, e), } }, } } debug!("router::{}: stopped", router_id); }); Self { id: id.to_owned(), req: req_tx, ctl: ctl_tx, handle: handle, } } /// Spawn an actor. pub fn spawn(&self, id: &str, f: Box<ActorFn>) -> Result<()> { let (spawn, resp) = RouterCtl::spawn(id, f); match self.ctl.send(spawn) { Ok(()) => match resp.recv() { Ok(()) => Ok(()), Err(e) => Err(Error::recv_error(e)), }, Err(e) => Err(Error::send_error(e)), } } /// Determine whether the router has a route to an actor, at the time of inspection. pub fn has(&self, id: &str) -> Result<bool> { let (has, resp) = RouterCtl::has(id); if let Err(e) = self.ctl.send(has) { return Err(Error::send_error(e)); } match resp.recv() { Ok(b) => Ok(b), Err(e) => Err(Error::recv_error(e)), } } /// Retrieve a copy of an actor's request channel `Sender`. pub fn get(&self, id: &str) -> Result<Sender<Message>> { let (get, resp) = RouterCtl::get(id); if let Err(e) = self.ctl.send(get) { return Err(Error::send_error(e)); } match resp.recv() { Ok(sender) => sender, Err(e) => Err(Error::recv_error(e)), } } /// Send a message to an actor. pub fn send(&self, id: &str, msg: Message) -> Result<()> { match self.req.send(RouterRequest::new(id, msg)) { Ok(()) => Ok(()), Err(e) => Err(Error::send_error(e)), } } /// Stop an actor. pub fn stop(&self, id: &str) -> Result<()> { let (stop, resp) = RouterCtl::stop_actor(id); if let Err(e) = self.ctl.send(stop) { return Err(Error::send_error(e)); } if let Err(e) = resp.recv() { return Err(Error::recv_error(e)); } Ok(()) } /// Stop an actor without waiting for it to stop. pub fn stop_async(&self, id: &str) -> Result<()> { if let Err(e) = self.ctl.send(RouterCtl::stop_actor_async(id)) { return Err(Error::send_error(e)); } Ok(()) } /// Stop a list of actors in order. pub fn stop_list(&self, ids: Vec<String>) -> Result<()> { for id in ids { if let Err(e) = self.stop(&id) { return Err(e); } } Ok(()) } /// Stop all actors and then stop the router. /// /// Note that actors are stopped in an arbitrary order. pub fn shutdown(self) { self.ctl.send(RouterCtl::Shutdown).unwrap(); self.handle.join().unwrap(); } } /// A request to route a message to an actor. /// /// The request consists of the ID of an actor previously spawned through the router and an /// arbitrary value to be sent to the actor, expressed as a boxed `Any + Send` trait object. pub struct RouterRequest { pub id: String, pub val: Box<dyn Any + Send>, } impl RouterRequest { /// Construct a `RouterRequest`. pub fn new(id: &str, val: Box<dyn Any + Send>) -> Self { RouterRequest { id: id.to_owned(), val: val, } } } /// A wrapper for sending a message to an actor. /// /// Sends a message to an actor through a [Router](struct.Router.html), possibly indirectly /// through an [ActorContext](struct.ActorContext.html). #[macro_export] macro_rules! send_actor { ($r:ident, $i:expr, $v:expr) => {{ $r.send($i, Box::new($v)) }}; } /// A control message for the router. /// /// These messages are processed directly by the router itself and control aspects of its /// operation. Notably, the router is responsible for creating actors and their threads and must /// receive a `RouterCtl::Spawn` request to do so. pub enum RouterCtl { /// Create a new actor managed by the router. Spawn { id: String, f: Box<ActorFn>, resp: Sender<()>, }, /// Retrieve the request channel for an actor from the router. Get { id: String, resp: Sender<Result<Sender<Message>>>, }, /// Determine whether or not the router has an actor. Has { id: String, resp: Sender<bool> }, /// Stop an actor. StopActor { id: String, resp: Sender<()> }, /// Stop an actor without waiting for it to stop. StopActorAsync(String), /// Stop all actors and then stop the router. Shutdown, } impl RouterCtl { /// Construct a `RouterCtl::Spawn` request. /// /// Returns the request object as well as a `Receiver` over which the router will send /// confirmation back to the requestor that the actor has been spawned. /// /// The `spawn_actor!` macro provides a more ergonomic wrapper around this method. pub fn spawn(id: &str, f: Box<ActorFn>) -> (Self, Receiver<()>) { let (tx, rx) = unbounded(); ( Self::Spawn { id: id.to_owned(), f: f, resp: tx, }, rx, ) } /// Construct a `RouterCtl::Get` request. /// /// Returns the request object as well as a `Receiver` over which the router will send back to /// the caller the `Sender` for the given actor (or `None`, if no such actor exists). /// /// The `get_actor!` macro provides a more ergonomic wrapper around this method. pub fn get(id: &str) -> (Self, Receiver<Result<Sender<Message>>>) { let (tx, rx) = unbounded(); ( Self::Get { id: id.to_owned(), resp: tx, }, rx, ) } /// Construct a `RouterCtl::Has` request. /// /// Returns the request object as well as a `Receiver` over which the router will send back a /// boolean to the caller that indicates whether or not the given actor is available at the /// time of its observation. /// /// The `has_actor!` macro provides a more ergonomic wrapper around this method. pub fn has(id: &str) -> (Self, Receiver<bool>) { let (tx, rx) = unbounded(); ( Self::Has { id: id.to_owned(), resp: tx, }, rx, ) } /// Construct a `RouterCtl::StopActor` request. /// /// Returns the request object as well as a `Receiver` over which the router will send /// confirmation back to the caller that the actor has stopped. pub fn stop_actor(id: &str) -> (Self, Receiver<()>) { let (tx, rx) = unbounded(); ( Self::StopActor { id: id.to_owned(), resp: tx, }, rx, ) } pub fn stop_actor_async(id: &str) -> Self { Self::StopActorAsync(id.to_owned()) } } /// A wrapper for executing a [RouterCtl::Spawn][RouterCtl] request on a [Router][Router]. /// /// Creates a `RouterCtl::Spawn` request, sends it to the router, and recieves the router's /// response. /// /// [RouterCtl]: enum.RouterCtl.html /// [Router]: struct.Router.html #[macro_export] macro_rules! spawn_actor { ($r:ident, $i:expr, $f:expr) => {{ $r.spawn($i, Box::new($f)) }}; } /// A handle to an actor. /// /// When the router constructs an actor it will encapsulate that actor's communication channels and /// its thread handle into an `Actor`. The router maps the ID of the actor to its `Actor` in its /// registry. pub struct Actor { pub id: String, pub req: Sender<Message>, pub ctl: Sender<ActorCtl>, pub handle: thread::JoinHandle<()>, } /// A signature for actor thread functions. /// /// Each actor thread, when spawned by the router, is passed an `ActorContext` that encapsulates /// the channels of communication available to the actor. Because the function is sent from the /// calling thread to the router thread, and then into a new thread for the actor, the function /// must be `Send`. The router wraps the invocation of the function to catch panics, so it can /// receive a status message indicating the function has paniced and clean up its resources, and as /// such must be `UnwindSafe` as well. pub type ActorFn = dyn FnOnce(ActorContext) + Send + UnwindSafe + 'static; /// A handle to communication channels provided to an actor function. /// /// Actor functions spawned through the router are passed an `ActorContext` that provides the /// `Receviers` over which the actor receives messages and control messages from the router and /// `Senders` the actor can use to communicate back with the router. /// /// This is typically only used by the router. pub struct ActorContext { pub id: String, pub req: Receiver<Message>, pub ctl: Receiver<ActorCtl>, pub router_req: Sender<RouterRequest>, pub router_ctl: Sender<RouterCtl>, pub stat: Sender<ActorStatus>, } impl ActorContext { /// Construct an `ActorContext`. This is typically used only by the router. pub fn new( id: String, req: Receiver<Message>, ctl: Receiver<ActorCtl>, router_req: Sender<RouterRequest>, router_ctl: Sender<RouterCtl>, stat: Sender<ActorStatus>, ) -> Self { Self { id: id.to_owned(), req: req, ctl: ctl, router_req: router_req, router_ctl: router_ctl, stat: stat, } } /// Spawn a new actor. pub fn spawn(&self, id: &str, f: Box<ActorFn>) -> Result<()> { let (spawn, resp) = RouterCtl::spawn(id, f); match self.router_ctl.send(spawn) { Ok(()) => match resp.recv() { Ok(()) => Ok(()), Err(e) => Err(Error::recv_error(e)), }, Err(e) => Err(Error::send_error(e)), } } /// Determine whether the router has a route to another actor, at the time of inspection. pub fn has(&self, id: &str) -> Result<bool> { let (has, resp) = RouterCtl::has(id); if let Err(e) = self.router_ctl.send(has) { return Err(Error::send_error(e)); } match resp.recv() { Ok(b) => Ok(b), Err(e) => Err(Error::recv_error(e)), } } /// Retrieve a copy of another actor's request channel `Sender`. pub fn get(&self, id: &str) -> Result<Sender<Message>> { let (get, resp) = RouterCtl::get(id); if let Err(e) = self.router_ctl.send(get) { return Err(Error::send_error(e)); } match resp.recv() { Ok(sender) => sender, Err(e) => Err(Error::recv_error(e)), } } /// Send a message to another actor. pub fn send(&self, id: &str, msg: Message) -> Result<()> { match self.router_req.send(RouterRequest::new(id, msg)) { Ok(()) => Ok(()), Err(e) => Err(Error::send_error(e)), } } /// Stop another actor. /// /// Warning: if attempting to stop another actor while in the process of being stopped, the /// router will be blocked awaiting a response. The router will not receive the stop request /// until after you have completed stopping and a deadlock will occur. pub fn stop(&self, id: &str) -> Result<()> { let (stop, resp) = RouterCtl::stop_actor(id); if let Err(e) = self.router_ctl.send(stop) { return Err(Error::send_error(e)); } match resp.recv() { Ok(()) => Ok(()), Err(e) => Err(Error::recv_error(e)), } } /// Stop another actor without waiting for it to stop. /// /// This should be used when stopping an actor from within an actor that is currently in the /// process of being stopped. pub fn stop_async(&self, id: &str) -> Result<()> { if let Err(e) = self.router_ctl.send(RouterCtl::stop_actor_async(id)) { return Err(Error::send_error(e)); } Ok(()) } /// Inform the router that we are stopping. pub fn report_stopped(&self) -> Result<()> { match self.stat.send(ActorStatus::Stopped(self.id.clone())) { Ok(_) => Ok(()), Err(e) => Err(Error::send_error(e)), } } } /// Messages that exhert control over actors. /// /// These messages are sent from the router to an actor thread. pub enum ActorCtl { /// The actor thread should stabilize its state, send an /// [ActorStatus::Stopped](enum.ActorStatus.html) to the router through its status channel, /// and exit. Stop, } /// Status messages sent from an actor to the supervising router. /// /// Each variant embeds the ID of the actor to which the message pertains. pub enum ActorStatus { /// The actor thread paniced. The panic is typically caught by the wrapper function the router /// uses around the actor thread, but actor functions may also catch their own panics and /// communicate them back to the router. Paniced(String), /// The actor thread has stopped or is in the process of stopping. This is typically send from /// the actor thread to the router immediately before it exits. Stopped(String), } /// Errors that can occur. #[derive(Debug)] pub enum Error { /// An error sending on a channel. /// /// Converts the underlying `crossbeam_channel::SendError` into a string representation to make /// it easier, if less flexible, to deal with. SendError(String), /// An error receiving on a channel. /// /// Converts the underlying `crossbeam_channel::RecvError` into a string representation to make /// it easier, if less flexible, to deal with. RecvError(String), /// The specified actor does not exist, or is not known to the router. Embeds the ID of the /// actor. /// /// If an actor thread panics or otherwise chooses to stop, it is removed from the router and /// subsequent attempts to send messages to that actor will result in this error. NoSuchActor(String), } impl Error { /// Construct an `Error::SendError` from an underlying `crossbeam_channel::SendError<T>`. pub fn send_error<T>(e: crossbeam_channel::SendError<T>) -> Self { Self::SendError(e.to_string()) } /// Construct an `Error::RecvError` from an underlying `crossbeam_channel::RecvError`. pub fn recv_error(e: crossbeam_channel::RecvError) -> Self { Self::RecvError(e.to_string()) } } impl fmt::Display for Error { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { match self { Self::SendError(e) => write!(f, "{}", e), Self::RecvError(e) => write!(f, "{}", e), Self::NoSuchActor(id) => write!(f, "no such actor: {}", id), } } } impl std::error::Error for Error { fn source(&self) -> Option<&(dyn std::error::Error + 'static)> { None } } #[cfg(test)] mod tests { use crate::prelude::*; #[test] fn basic_router() { let router = Router::run("test"); assert!(!router.has("foo").unwrap()); spawn_actor!(router, "foo", |ctx: ActorContext| { ctx.ctl.recv().unwrap(); ctx.report_stopped().unwrap(); }) .unwrap(); assert!(router.has("foo").unwrap()); router.stop("foo").unwrap(); assert!(!router.has("foo").unwrap()); router.shutdown(); } }