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//! Sync Actors support
//!
//! Sync Actors are actors that run multiple instances on a thread pool.
//! This is useful for CPU bound, or concurrent workloads. There can only be
//! a single Sync Actor type on a `SyncArbiter`. This means you can't have
//! Actor type A and B, sharing the same thread pool. You need to create two
//! [`SyncArbiter`]s and have A and B spawn on unique `SyncArbiter`s respectively.
//! For more information and examples, see `SyncArbiter`
use std::{future::Future, pin::Pin, sync::Arc, task, task::Poll, thread};
use actix_rt::System;
use crossbeam_channel as cb_channel;
use futures_core::stream::Stream;
use log::warn;
use tokio::sync::oneshot::Sender as SyncSender;
use crate::{
actor::{Actor, ActorContext, ActorState, Running},
address::{
channel, Addr, AddressReceiver, AddressSenderProducer, Envelope, EnvelopeProxy, ToEnvelope,
},
context::Context,
handler::{Handler, Message, MessageResponse},
};
/// [`SyncArbiter`] provides the resources for a single Sync Actor to run on a dedicated
/// thread or threads. This is generally used for CPU bound concurrent workloads. It's
/// important to note, that the [`SyncArbiter`] generates a single address for the pool
/// of hosted Sync Actors. Any message sent to this Address, will be operated on by
/// a single Sync Actor from the pool.
///
/// Sync Actors have a different lifecycle compared to Actors on the System
/// Arbiter. For more, see `SyncContext`.
///
/// # Examples
///
/// ```
/// use actix::prelude::*;
///
/// struct Fibonacci(pub u32);
///
/// # impl Message for Fibonacci {
/// # type Result = Result<u64, ()>;
/// # }
///
/// struct SyncActor;
///
/// impl Actor for SyncActor {
/// // It's important to note that you use "SyncContext" here instead of "Context".
/// type Context = SyncContext<Self>;
/// }
///
/// impl Handler<Fibonacci> for SyncActor {
/// type Result = Result<u64, ()>;
///
/// fn handle(&mut self, msg: Fibonacci, _: &mut Self::Context) -> Self::Result {
/// if msg.0 == 0 {
/// Err(())
/// } else if msg.0 == 1 {
/// Ok(1)
/// } else {
/// let mut i = 0;
/// let mut sum = 0;
/// let mut last = 0;
/// let mut curr = 1;
/// while i < msg.0 - 1 {
/// sum = last + curr;
/// last = curr;
/// curr = sum;
/// i += 1;
/// }
/// Ok(sum)
/// }
/// }
/// }
///
/// fn main() {
/// System::new().block_on(async {
/// // Start the SyncArbiter with 2 threads, and receive the address of the Actor pool.
/// let addr = SyncArbiter::start(2, || SyncActor);
///
/// // send 5 messages
/// for n in 5..10 {
/// // As there are 2 threads, there are at least 2 messages always being processed
/// // concurrently by the SyncActor.
/// addr.do_send(Fibonacci(n));
/// }
///
/// # System::current().stop();
/// });
/// }
/// ```
pub struct SyncArbiter<A>
where
A: Actor<Context = SyncContext<A>>,
{
queue: Option<cb_channel::Sender<Envelope<A>>>,
msgs: AddressReceiver<A>,
}
impl<A> SyncArbiter<A>
where
A: Actor<Context = SyncContext<A>>,
{
/// Start a new `SyncArbiter` with specified number of worker threads.
/// Returns a single address of the started actor. A single address is
/// used to communicate to the actor(s), and messages are handled by
/// the next available Actor in the `SyncArbiter`.
pub fn start<F>(threads: usize, factory: F) -> Addr<A>
where
F: Fn() -> A + Send + Sync + 'static,
{
Self::start_with_thread_builder(threads, thread::Builder::new, factory)
}
/// Start a new `SyncArbiter` with specified number of worker threads.
/// Each worker thread is spawned from the [`std::thread::Builder`]
/// returned by a new call to `thread_builder_factory`.
/// Returns a single address of the started actor. A single address is
/// used to communicate to the actor(s), and messages are handled by
/// the next available Actor in the `SyncArbiter`.
pub fn start_with_thread_builder<F, BF>(
threads: usize,
mut thread_builder_factory: BF,
factory: F,
) -> Addr<A>
where
F: Fn() -> A + Send + Sync + 'static,
BF: FnMut() -> thread::Builder,
{
let factory = Arc::new(factory);
let (sender, receiver) = cb_channel::unbounded();
let (tx, rx) = channel::channel(0);
for _ in 0..threads {
let f = Arc::clone(&factory);
let sys = System::current();
let actor_queue = receiver.clone();
let inner_rx = rx.sender_producer();
thread_builder_factory()
.spawn(move || {
System::set_current(sys);
SyncContext::new(f, actor_queue, inner_rx).run();
})
.expect("failed to spawn thread");
}
System::current().arbiter().spawn(Self {
queue: Some(sender),
msgs: rx,
});
Addr::new(tx)
}
}
impl<A> Actor for SyncArbiter<A>
where
A: Actor<Context = SyncContext<A>>,
{
type Context = Context<Self>;
}
#[doc(hidden)]
impl<A> Future for SyncArbiter<A>
where
A: Actor<Context = SyncContext<A>>,
{
type Output = ();
fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
let this = self.get_mut();
loop {
match Pin::new(&mut this.msgs).poll_next(cx) {
Poll::Ready(Some(msg)) => {
if let Some(ref queue) = this.queue {
assert!(queue.send(msg).is_ok());
}
}
Poll::Pending => break,
Poll::Ready(None) => unreachable!(),
}
}
// stop condition
if this.msgs.connected() {
Poll::Pending
} else {
// stop sync arbiters
this.queue = None;
Poll::Ready(())
}
}
}
impl<A, M> ToEnvelope<A, M> for SyncContext<A>
where
A: Actor<Context = Self> + Handler<M>,
M: Message + Send + 'static,
M::Result: Send,
{
fn pack(msg: M, tx: Option<SyncSender<M::Result>>) -> Envelope<A> {
Envelope::with_proxy(Box::new(SyncContextEnvelope::new(msg, tx)))
}
}
/// Sync actor execution context. This is used instead of impl Actor for your Actor
/// instead of Context, if you intend this actor to run in a [`SyncArbiter`].
///
/// Unlike Context, an Actor that uses a [`SyncContext`] can not be stopped
/// by calling `stop` or `terminate`: Instead, these trigger a restart of
/// the Actor. Similar, returning `false` from `fn stopping` can not prevent
/// the restart or termination of the Actor.
///
/// # Examples
///
/// ```
/// use actix::prelude::*;
///
/// # struct Fibonacci(pub u32);
///
/// # impl Message for Fibonacci {
/// # type Result = Result<u64, ()>;
/// # }
///
/// struct SyncActor;
///
/// impl Actor for SyncActor {
/// // It's important to note that you use "SyncContext" here instead of "Context".
/// type Context = SyncContext<Self>;
/// }
///
/// # fn main() {
/// # }
/// ```
pub struct SyncContext<A>
where
A: Actor<Context = SyncContext<A>>,
{
act: Option<A>,
queue: cb_channel::Receiver<Envelope<A>>,
stopping: bool,
state: ActorState,
factory: Arc<dyn Fn() -> A>,
address: AddressSenderProducer<A>,
}
impl<A> SyncContext<A>
where
A: Actor<Context = Self>,
{
fn new(
factory: Arc<dyn Fn() -> A>,
queue: cb_channel::Receiver<Envelope<A>>,
address: AddressSenderProducer<A>,
) -> Self {
let act = factory();
Self {
queue,
factory,
act: Some(act),
stopping: false,
state: ActorState::Started,
address,
}
}
fn run(&mut self) {
let mut act = self.act.take().unwrap();
// started
A::started(&mut act, self);
self.state = ActorState::Running;
loop {
match self.queue.recv() {
Ok(mut env) => {
env.handle(&mut act, self);
}
Err(_) => {
self.state = ActorState::Stopping;
if A::stopping(&mut act, self) != Running::Stop {
warn!("stopping method is not supported for sync actors");
}
self.state = ActorState::Stopped;
A::stopped(&mut act, self);
return;
}
}
if self.stopping {
self.stopping = false;
// stop old actor
A::stopping(&mut act, self);
self.state = ActorState::Stopped;
A::stopped(&mut act, self);
// start new actor
self.state = ActorState::Started;
act = (*self.factory)();
A::started(&mut act, self);
self.state = ActorState::Running;
}
}
}
pub fn address(&self) -> Addr<A> {
Addr::new(self.address.sender())
}
}
impl<A> ActorContext for SyncContext<A>
where
A: Actor<Context = Self>,
{
/// Stop the current Actor. [`SyncContext`] will stop the existing Actor, and restart
/// a new Actor of the same type to replace it.
fn stop(&mut self) {
self.stopping = true;
self.state = ActorState::Stopping;
}
/// Terminate the current Actor. [`SyncContext`] will terminate the existing Actor, and restart
/// a new Actor of the same type to replace it.
fn terminate(&mut self) {
self.stopping = true;
self.state = ActorState::Stopping;
}
/// Get the Actor execution state.
fn state(&self) -> ActorState {
self.state
}
}
pub(crate) struct SyncContextEnvelope<M>
where
M: Message + Send,
{
msg: Option<M>,
tx: Option<SyncSender<M::Result>>,
}
impl<M> SyncContextEnvelope<M>
where
M: Message + Send,
M::Result: Send,
{
pub fn new(msg: M, tx: Option<SyncSender<M::Result>>) -> Self {
Self { tx, msg: Some(msg) }
}
}
impl<A, M> EnvelopeProxy<A> for SyncContextEnvelope<M>
where
M: Message + Send + 'static,
M::Result: Send,
A: Actor<Context = SyncContext<A>> + Handler<M>,
{
fn handle(&mut self, act: &mut A, ctx: &mut A::Context) {
let tx = self.tx.take();
if tx.is_some() && tx.as_ref().unwrap().is_closed() {
return;
}
if let Some(msg) = self.msg.take() {
<A as Handler<M>>::handle(act, msg, ctx).handle(ctx, tx)
}
}
}
#[cfg(test)]
mod tests {
use tokio::sync::oneshot;
use crate::prelude::*;
struct SyncActor2;
impl Actor for SyncActor2 {
type Context = SyncContext<Self>;
}
struct SyncActor1(Addr<SyncActor2>);
impl Actor for SyncActor1 {
type Context = SyncContext<Self>;
}
impl SyncActor1 {
fn run() -> SyncActor1 {
SyncActor1(SyncArbiter::start(1, || SyncActor2))
}
}
struct Msg(oneshot::Sender<u8>);
impl Message for Msg {
type Result = ();
}
impl Handler<Msg> for SyncActor1 {
type Result = ();
fn handle(&mut self, msg: Msg, _: &mut Self::Context) -> Self::Result {
self.0.do_send(msg);
}
}
impl Handler<Msg> for SyncActor2 {
type Result = ();
fn handle(&mut self, msg: Msg, _: &mut Self::Context) -> Self::Result {
msg.0.send(233u8).unwrap();
}
}
#[test]
fn nested_sync_arbiters() {
System::new().block_on(async {
let addr = SyncArbiter::start(1, SyncActor1::run);
let (tx, rx) = oneshot::channel();
addr.send(Msg(tx)).await.unwrap();
assert_eq!(233u8, rx.await.unwrap());
System::current().stop();
})
}
}