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//! # Services
//!
//! Interlink uses services to represent asynchronous tasks that can hold their
//! own state and communicate between each-other using messages and handlers.
//!
//! You can derive the service trait using its derive macro or implement it
//! manually to get access to the [`Service::started`] and [`Service::stopping`]
//! functions.
//!
//! With derive macro:
//! ```
//! use interlink::prelude::*;
//!
//! #[derive(Service)]
//! struct MyService {
//! value: String,
//! }
//! ```
//!
//! Without derive macro. Both the started and stopping functions are optional
//! ```
//! use interlink::prelude::*;
//!
//! struct MyService {
//! value: String,
//! }
//!
//! impl Service for MyService {
//! fn started(&mut self, ctx: &mut ServiceContext<Self>) {
//! println!("My service is started")
//! }
//! }
//! ```
//!
//! Then you can start your service using the [`Service::start`] function which will
//! start the service in a tokio task and return you a [`Link`] to the service. Alternatively
//! if you need access to the service context while creating your service you can use the
//! [`Service::create`] function which provides the context.
//!
//! See [`Link`] for what to do from here
use std::time::Duration;
use crate::envelope::{ServiceAction, ServiceMessage};
use crate::link::Link;
use tokio::sync::mpsc;
use tokio::task::JoinHandle;
use tokio::time::sleep;
/// Trait implemented by structures that can be spawned as
/// services and used by the app
#[allow(unused_variables)]
pub trait Service: Sized + Send + 'static {
/// Handler called before the service starts processing messages
///
/// `ctx` The service context
fn started(&mut self, ctx: &mut ServiceContext<Self>) {}
/// Start an already created service and provides a link for
/// communicating with the service
///
/// ```
/// use interlink::prelude::*;
///
/// #[derive(Service)]
/// struct MyService;
///
/// #[tokio::main]
/// async fn main() {
/// // Create the service
/// let service: MyService = MyService {};
/// // Start the service and obtain a link to it
/// let addr: Link<MyService> = service.start();
/// }
/// ```
fn start(self) -> Link<Self> {
let ctx = ServiceContext::new();
let link = ctx.link();
ctx.spawn(self);
link
}
/// Alternative way of creating a service where the service may
/// rely on the context an example of this is an associated service
/// which requires a link to the service but is also stored on the
/// service struct
///
/// ```
/// use interlink::prelude::*;
///
/// #[derive(Service)]
/// struct First {
/// /// Link to spawned service
/// second: Link<Second>,
/// }
///
/// /// Some other service which requires a link to our service
/// #[derive(Service)]
/// struct Second {
/// /// Link to the service that owns this service
/// owner: Link<First>
/// }
///
/// #[tokio::main]
/// async fn main() {
/// // Provide a closure which takes in the ctx
/// let link: Link<First> = First::create(|ctx| {
///
/// // Create second which references the context
/// let second: Link<Second> = Second {
/// owner: ctx.link()
/// }
/// .start();
///
/// // Can now use the spawned value
/// First { second }
/// });
/// }
/// ```
fn create<F>(action: F) -> Link<Self>
where
F: FnOnce(&mut ServiceContext<Self>) -> Self,
{
let mut ctx = ServiceContext::new();
let service = action(&mut ctx);
let link = ctx.link();
ctx.spawn(service);
link
}
/// Handler logic called when the service is stopping
fn stopping(&mut self) {}
}
/// Backing context for a service which handles storing the
/// reciever for messaging and the original link for spawning
/// copies
pub struct ServiceContext<S: Service> {
/// Reciever for handling incoming messages for the service
rx: mpsc::UnboundedReceiver<ServiceMessage<S>>,
/// The original link cloned to create other links to the service
link: Link<S>,
}
impl<S> ServiceContext<S>
where
S: Service,
{
/// Creates a new service context and the initial link
pub(crate) fn new() -> ServiceContext<S> {
let (tx, rx) = mpsc::unbounded_channel();
let link = Link(tx);
ServiceContext { rx, link }
}
/// Spawns this service into a new tokio task
/// where it will then begin processing messages
///
/// `service` The service
pub(crate) fn spawn(mut self, mut service: S) {
tokio::spawn(async move {
service.started(&mut self);
self.process(&mut service).await;
service.stopping();
});
}
/// Processing loop for the service handles recieved messages and
/// executing actions from the message handle results
///
/// `service` The service this context is processing for
async fn process(&mut self, service: &mut S) {
while let Some(msg) = self.rx.recv().await {
let action = msg.handle(service, self);
match action {
ServiceAction::Stop => break,
ServiceAction::Continue => continue,
// Execute tasks that require blocking the processing
ServiceAction::Execute(fut) => fut.await,
}
}
}
/// Stop the context directly by closing the reciever the
/// reciever will drain any existing messages until there
/// are none remaining
pub fn stop(&mut self) {
self.rx.close()
}
/// Creates and returns a link to the service
pub fn link(&self) -> Link<S> {
self.link.clone()
}
/// Returns a reference to the shared link used by this context
/// for creating new links. You can use this to access the service
/// link without creating a clone of it
pub fn shared_link(&self) -> &Link<S> {
&self.link
}
/// Executes the provided `action` function on the service and service context
/// after the provided `duration` has elapsed. This function returns a [`JoinHandle`]
/// which you can use to stop the task by calling .abort() on the handle
///
/// ```
/// use interlink::prelude::*;
/// use std::time::Duration;
/// use tokio::time::sleep;
///
/// struct Test {
/// value: u32,
/// }
///
/// impl Service for Test {
/// fn started(&mut self, ctx: &mut ServiceContext<Self>) {
/// ctx.run_later(Duration::from_secs(1), |service, _ctx| {
/// println!("Hello 1 second later from the service: {}", service.value);
/// service.value += 1;
/// });
/// }
/// }
///
/// #[tokio::test]
/// async fn test() {
/// let link = Test { value: 1 }.start();
///
/// sleep(Duration::from_secs(5)).await;
/// }
/// ```
pub fn run_later<F>(&self, duration: Duration, action: F) -> JoinHandle<()>
where
F: FnOnce(&mut S, &mut ServiceContext<S>) + Send + 'static,
{
let link = self.link();
tokio::spawn(async move {
sleep(duration).await;
let _ = link.do_exec(action);
})
}
/// Executes the provided `action` function on the service and service context
/// every time the `duration` is elapsed. This function returns a [`JoinHandle`]
/// which you can use to stop the task by calling .abort() on the handle
///
/// ```
/// use interlink::prelude::*;
/// use std::time::Duration;
/// use tokio::time::sleep;
///
/// struct Test {
/// value: u32,
/// }
///
/// impl Service for Test {
/// fn started(&mut self, ctx: &mut ServiceContext<Self>) {
/// ctx.run_interval(Duration::from_secs(1), |service, _ctx| {
/// println!(
/// "Hello at 1 second interval from the service: {}",
/// service.value
/// );
/// service.value += 1;
/// });
/// }
/// }
///
/// #[tokio::test]
/// async fn test() {
/// let link = Test { value: 1 }.start();
///
/// sleep(Duration::from_secs(15)).await;
/// }
/// ```
pub fn run_interval<F>(&self, duration: Duration, action: F) -> JoinHandle<()>
where
F: FnOnce(&mut S, &mut ServiceContext<S>) + Clone + Send + 'static,
{
let link = self.link();
tokio::spawn(async move {
loop {
sleep(duration).await;
if link.do_exec(action.clone()).is_err() {
break;
}
}
})
}
}