Feature: Add MPSC channel to AsyncRuntime

`AsyncRuntime` trait defines the async-runtime such as tokio to run
Openraft. This commit add MPSC abstraction to `AsyncRuntime` and
MPSC implementations to tokio based runtime and monoio based runtime.

openraft/src/testing/runtime/mod.rs

@@ -7,7 +7,11 @@ use std::task::Poll;
 
 use crate::async_runtime::watch::WatchReceiver;
 use crate::async_runtime::watch::WatchSender;
+use crate::async_runtime::Mpsc;
+use crate::async_runtime::MpscReceiver;
+use crate::async_runtime::MpscSender;
 use crate::async_runtime::MpscUnboundedWeakSender;
+use crate::async_runtime::MpscWeakSender;
 use crate::instant::Instant;
 use crate::type_config::async_runtime::mpsc_unbounded::MpscUnbounded;
 use crate::type_config::async_runtime::mpsc_unbounded::MpscUnboundedReceiver;
@@ -43,11 +47,19 @@ impl<Rt: AsyncRuntime> Suite<Rt> {
         Self::test_sleep_until().await;
         Self::test_timeout().await;
         Self::test_timeout_at().await;
+
+        Self::test_mpsc_recv_empty().await;
+        Self::test_mpsc_recv_channel_closed().await;
+        Self::test_mpsc_weak_sender_wont_prevent_channel_close().await;
+        Self::test_mpsc_weak_sender_upgrade().await;
+        Self::test_mpsc_send().await;
+
         Self::test_unbounded_mpsc_recv_empty().await;
         Self::test_unbounded_mpsc_recv_channel_closed().await;
         Self::test_unbounded_mpsc_weak_sender_wont_prevent_channel_close().await;
         Self::test_unbounded_mpsc_weak_sender_upgrade().await;
         Self::test_unbounded_mpsc_send().await;
+
         Self::test_watch_init_value().await;
         Self::test_watch_overwrite_init_value().await;
         Self::test_watch_send_error_no_receiver().await;
@@ -131,6 +143,77 @@ impl<Rt: AsyncRuntime> Suite<Rt> {
         assert!(timeout_result.is_err());
     }
 
+    pub async fn test_mpsc_recv_empty() {
+        let (_tx, mut rx) = Rt::Mpsc::channel::<()>(5);
+        let recv_err = rx.try_recv().unwrap_err();
+        assert!(matches!(recv_err, TryRecvError::Empty));
+    }
+
+    pub async fn test_mpsc_recv_channel_closed() {
+        let (_, mut rx) = Rt::Mpsc::channel::<()>(5);
+        let recv_err = rx.try_recv().unwrap_err();
+        assert!(matches!(recv_err, TryRecvError::Disconnected));
+
+        let recv_result = rx.recv().await;
+        assert!(recv_result.is_none());
+    }
+
+    pub async fn test_mpsc_weak_sender_wont_prevent_channel_close() {
+        let (tx, mut rx) = Rt::Mpsc::channel::<()>(5);
+
+        let _weak_tx = tx.downgrade();
+        drop(tx);
+        let recv_err = rx.try_recv().unwrap_err();
+        assert!(matches!(recv_err, TryRecvError::Disconnected));
+
+        let recv_result = rx.recv().await;
+        assert!(recv_result.is_none());
+    }
+
+    pub async fn test_mpsc_weak_sender_upgrade() {
+        let (tx, _rx) = Rt::Mpsc::channel::<()>(5);
+
+        let weak_tx = tx.downgrade();
+        let opt_tx = weak_tx.upgrade();
+        assert!(opt_tx.is_some());
+
+        drop(tx);
+        drop(opt_tx);
+        // now there is no Sender instances alive
+
+        let opt_tx = weak_tx.upgrade();
+        assert!(opt_tx.is_none());
+    }
+
+    pub async fn test_mpsc_send() {
+        let (tx, mut rx) = Rt::Mpsc::channel::<usize>(5);
+        let tx = Arc::new(tx);
+
+        let n_senders = 10_usize;
+        let recv_expected = (0..n_senders).collect::<Vec<_>>();
+
+        for idx in 0..n_senders {
+            let tx = tx.clone();
+            // no need to wait for senders here, we wait by recv()ing
+            let _handle = Rt::spawn(async move {
+                tx.send(idx).await.unwrap();
+            });
+        }
+
+        let mut recv = Vec::with_capacity(n_senders);
+        while let Some(recv_number) = rx.recv().await {
+            recv.push(recv_number);
+
+            if recv.len() == n_senders {
+                break;
+            }
+        }
+
+        recv.sort();
+
+        assert_eq!(recv_expected, recv);
+    }
+
     pub async fn test_unbounded_mpsc_recv_empty() {
         let (_tx, mut rx) = Rt::MpscUnbounded::channel::<()>();
         let recv_err = rx.try_recv().unwrap_err();

openraft/src/type_config/async_runtime/mod.rs

@@ -9,6 +9,7 @@ pub(crate) mod tokio_impls {
     mod tokio_runtime;
     pub use tokio_runtime::TokioRuntime;
 }
+pub mod mpsc;
 pub mod mpsc_unbounded;
 pub mod mutex;
 pub mod oneshot;
@@ -19,6 +20,10 @@ use std::fmt::Display;
 use std::future::Future;
 use std::time::Duration;
 
+pub use mpsc::Mpsc;
+pub use mpsc::MpscReceiver;
+pub use mpsc::MpscSender;
+pub use mpsc::MpscWeakSender;
 pub use mpsc_unbounded::MpscUnbounded;
 pub use mpsc_unbounded::MpscUnboundedReceiver;
 pub use mpsc_unbounded::MpscUnboundedSender;
@@ -99,6 +104,8 @@ pub trait AsyncRuntime: Debug + Default + PartialEq + Eq + OptionalSend + Option
     /// sent to another thread.
     fn thread_rng() -> Self::ThreadLocalRng;
 
+    type Mpsc: Mpsc;
+
     type MpscUnbounded: MpscUnbounded;
 
     type Watch: Watch;

openraft/src/type_config/async_runtime/mpsc/mod.rs

@@ -0,0 +1,73 @@
+use std::future::Future;
+
+use base::OptionalSend;
+use base::OptionalSync;
+
+/// mpsc shares the same error types as mpsc_unbounded
+pub use super::mpsc_unbounded::SendError;
+pub use super::mpsc_unbounded::TryRecvError;
+use crate::base;
+
+/// Multi-producer, single-consumer channel.
+pub trait Mpsc: Sized + OptionalSend {
+    type Sender<T: OptionalSend>: MpscSender<Self, T>;
+    type Receiver<T: OptionalSend>: MpscReceiver<T>;
+    type WeakSender<T: OptionalSend>: MpscWeakSender<Self, T>;
+
+    /// Creates an unbounded mpsc channel for communicating between asynchronous
+    /// tasks without backpressure.
+    fn channel<T: OptionalSend>(buffer: usize) -> (Self::Sender<T>, Self::Receiver<T>);
+}
+
+/// Send values to the associated [`MpscReceiver`].
+pub trait MpscSender<MU, T>: OptionalSend + OptionalSync + Clone
+where
+    MU: Mpsc,
+    T: OptionalSend,
+{
+    /// Attempts to send a message without blocking.
+    ///
+    /// If the receiving half of the channel is closed, this
+    /// function returns an error. The error includes the value passed to `send`.
+    fn send(&self, msg: T) -> impl Future<Output = Result<(), SendError<T>>> + OptionalSend;
+
+    /// Converts the [`MpscSender`] to a [`MpscWeakSender`] that does not count
+    /// towards RAII semantics, i.e. if all `Sender` instances of the
+    /// channel were dropped and only `WeakSender` instances remain,
+    /// the channel is closed.
+    fn downgrade(&self) -> MU::WeakSender<T>;
+}
+
+/// Receive values from the associated [`MpscSender`].
+pub trait MpscReceiver<T>: OptionalSend + OptionalSync {
+    /// Receives the next value for this receiver.
+    ///
+    /// This method returns `None` if the channel has been closed and there are
+    /// no remaining messages in the channel's buffer.
+    fn recv(&mut self) -> impl Future<Output = Option<T>> + OptionalSend;
+
+    /// Tries to receive the next value for this receiver.
+    ///
+    /// This method returns the [`TryRecvError::Empty`] error if the channel is currently
+    /// empty, but there are still outstanding senders.
+    ///
+    /// This method returns the [`TryRecvError::Disconnected`] error if the channel is
+    /// currently empty, and there are no outstanding senders.
+    fn try_recv(&mut self) -> Result<T, TryRecvError>;
+}
+
+/// A sender that does not prevent the channel from being closed.
+///
+/// If all [`MpscSender`] instances of a channel were dropped and only
+/// `WeakSender` instances remain, the channel is closed.
+pub trait MpscWeakSender<MU, T>: OptionalSend + OptionalSync + Clone
+where
+    MU: Mpsc,
+    T: OptionalSend,
+{
+    /// Tries to convert a [`MpscWeakSender`] into an [`MpscSender`].
+    ///
+    /// This will return `Some` if there are other `Sender` instances alive and
+    /// the channel wasn't previously dropped, otherwise `None` is returned.
+    fn upgrade(&self) -> Option<MU::Sender<T>>;
+}

openraft/src/type_config/async_runtime/tokio_impls/tokio_runtime.rs

@@ -74,6 +74,7 @@ impl AsyncRuntime for TokioRuntime {
         rand::thread_rng()
     }
 
+    type Mpsc = mpsc_impl::TokioMpsc;
     type MpscUnbounded = TokioMpscUnbounded;
     type Watch = TokioWatch;
     type Oneshot = TokioOneshot;
@@ -134,6 +135,75 @@ where T: OptionalSend
     }
 }
 
+mod mpsc_impl {
+    use std::future::Future;
+
+    use futures::TryFutureExt;
+    use tokio::sync::mpsc;
+
+    use crate::async_runtime::Mpsc;
+    use crate::async_runtime::MpscReceiver;
+    use crate::async_runtime::MpscSender;
+    use crate::async_runtime::MpscWeakSender;
+    use crate::async_runtime::SendError;
+    use crate::async_runtime::TryRecvError;
+    use crate::OptionalSend;
+
+    pub struct TokioMpsc;
+
+    impl Mpsc for TokioMpsc {
+        type Sender<T: OptionalSend> = mpsc::Sender<T>;
+        type Receiver<T: OptionalSend> = mpsc::Receiver<T>;
+        type WeakSender<T: OptionalSend> = mpsc::WeakSender<T>;
+
+        /// Creates an unbounded mpsc channel for communicating between asynchronous
+        /// tasks without backpressure.
+        fn channel<T: OptionalSend>(buffer: usize) -> (Self::Sender<T>, Self::Receiver<T>) {
+            mpsc::channel(buffer)
+        }
+    }
+
+    impl<T> MpscSender<TokioMpsc, T> for mpsc::Sender<T>
+    where T: OptionalSend
+    {
+        #[inline]
+        fn send(&self, msg: T) -> impl Future<Output = Result<(), SendError<T>>> + OptionalSend {
+            self.send(msg).map_err(|e| SendError(e.0))
+        }
+
+        #[inline]
+        fn downgrade(&self) -> <TokioMpsc as Mpsc>::WeakSender<T> {
+            self.downgrade()
+        }
+    }
+
+    impl<T> MpscReceiver<T> for mpsc::Receiver<T>
+    where T: OptionalSend
+    {
+        #[inline]
+        fn recv(&mut self) -> impl Future<Output = Option<T>> + OptionalSend {
+            self.recv()
+        }
+
+        #[inline]
+        fn try_recv(&mut self) -> Result<T, TryRecvError> {
+            self.try_recv().map_err(|e| match e {
+                mpsc::error::TryRecvError::Empty => TryRecvError::Empty,
+                mpsc::error::TryRecvError::Disconnected => TryRecvError::Disconnected,
+            })
+        }
+    }
+
+    impl<T> MpscWeakSender<TokioMpsc, T> for mpsc::WeakSender<T>
+    where T: OptionalSend
+    {
+        #[inline]
+        fn upgrade(&self) -> Option<<TokioMpsc as Mpsc>::Sender<T>> {
+            self.upgrade()
+        }
+    }
+}
+
 pub struct TokioWatch;
 
 impl watch::Watch for TokioWatch {

rt-monoio/Cargo.toml

@@ -18,6 +18,9 @@ repository = "https://github.com/datafuselabs/openraft"
 openraft = { path = "../openraft", version = "0.10.0", default-features = false, features = ["singlethreaded"] }
 
 rand = "0.8"
-tokio = { version = "1.22", features = ["sync"] }
-monoio = "0.2.3"
+
+futures = { version = "0.3" }
 local-sync = "0.1.1"
+
+monoio = "0.2.3"
+tokio = { version = "1.22", features = ["sync"] }