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//! The [`Chan`] type is defined here. Typically, you don't need to import this module, and should //! use the [`Chan`](super::Chan) type synonym instead. use futures::Future; use pin_project::pin_project; use std::{ any::TypeId, convert::{TryFrom, TryInto}, marker::{self, PhantomData}, mem, pin::Pin, sync::{Arc, Mutex}, task::{Context, Poll}, }; use crate::tuple::{HasLength, List, Tuple}; use crate::Unavailable; use crate::{backend::*, IncompleteHalf, SessionIncomplete}; use crate::{prelude::*, types::*, unary::*}; /// A bidirectional communications channel using the session type `P` over the connections `Tx` and /// `Rx`. /// /// # Creating new `Chan`s: use [`Session`] /// /// The [`Session`] trait is implemented for all valid session types. To create a new [`Chan`] for /// some session type, use one of the provided static methods. Here, we create two `Chan`s with the /// session type `send String` and its dual `recv String`, wrapping an underlying bidirectional /// transport built from a pair of [`tokio::sync::mpsc::channel`][mpsc]s: /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// // Make a pair of channels: /// // - `c1` with the session type `send String`, and /// // - `c2` with the dual session type `recv String` /// let (c1, c2) = <Session! { send String }>::channel(|| mpsc::channel(1)); /// # Ok(()) /// # } /// ``` /// /// If you already have a sender and receiver and want to wrap them in a `Chan`, use the /// [`wrap`](crate::Session::wrap) method for a session type. This is useful, for example, if you're /// talking to another process over a network connection, where it's not possible to build both /// halves of the channel on one computer, and instead each computer will wrap one end of the /// connection: /// /// ```ignore /// # use dialectic::prelude::*; /// # use dialectic_tokio_mpsc as mpsc; /// # /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// let (tx, rx) = /* ... */; /// let c = <Session! { send String }>::wrap(tx, rx); /// # Ok(()) /// # } /// ``` /// /// [`Session`]: trait@crate::Session /// [mpsc]: https://docs.rs/tokio/latest/tokio/sync/mpsc/index.html #[derive(Derivative)] #[derivative(Debug)] #[repr(C)] #[must_use] pub struct Chan<S: Session, Tx: marker::Send + 'static, Rx: marker::Send + 'static> { tx: Option<Tx>, rx: Option<Rx>, drop_tx: Arc<Mutex<Result<Tx, IncompleteHalf<Tx>>>>, drop_rx: Arc<Mutex<Result<Rx, IncompleteHalf<Rx>>>>, session: PhantomData<fn() -> S>, } impl<Tx, Rx, S> Drop for Chan<S, Tx, Rx> where Tx: marker::Send + 'static, Rx: marker::Send + 'static, S: Session, { fn drop(&mut self) { let done = TypeId::of::<<S as Session>::Action>() == TypeId::of::<Done>(); if let Some(tx) = self.tx.take() { *self.drop_tx.lock().unwrap() = if done { Ok(tx) } else { Err(IncompleteHalf::Unfinished(tx)) }; } if let Some(rx) = self.rx.take() { *self.drop_rx.lock().unwrap() = if done { Ok(rx) } else { Err(IncompleteHalf::Unfinished(rx)) }; } } } impl<Tx, Rx, S> Chan<S, Tx, Rx> where S: Session, Tx: marker::Send + 'static, Rx: marker::Send + 'static, { /// Close a finished session, dropping the underlying connections. /// /// If called inside a future given to [`split`](Chan::split) or [`call`](Chan::call), the /// underlying connections are implicitly recovered for use in subsequent actions in the /// session, or if called in a future given to in [`over`](Session::over), are returned to the /// caller. /// /// # Examples /// /// Starting with a channel whose session type is already [`Done`], we can immediately close the /// channel. /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() { /// let (c1, c2) = <Session! {}>::channel(mpsc::unbounded_channel); /// c1.close(); /// c2.close(); /// # } /// ``` /// /// However, if the channel's session type is *not* `Done`, it is a type error to attempt to /// close the channel. The following code will not compile: /// /// ```compile_fail /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() { /// let (c1, c2) = <Session! { loop { send String } }>::channel(mpsc::unbounded_channel); /// c1.close(); /// c2.close(); /// # } /// ``` /// /// If you *really* want to destruct a channel before the end of its session, use /// [`into_inner`](Chan::into_inner), but beware that this may cause the party on the other end /// of the channel to throw errors due to your violation of the channel's protocol! pub fn close(self) where S: Session<Action = Done>, { drop(self) } /// Receive something of type `T` on the channel, returning the pair of the received object and /// the channel. /// /// # Errors /// /// This function returns the [`Receiver::Error`] for the underlying `Rx` connection if there /// was an error while receiving. /// /// # Examples /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// let (c1, c2) = <Session! { recv String }>::channel(|| mpsc::channel(1)); /// c2.send("Hello, world!".to_string()).await?; /// /// let (s, c1) = c1.recv().await?; /// assert_eq!(s, "Hello, world!"); /// # Ok(()) /// # } /// ``` pub async fn recv<T, P>(mut self) -> Result<(T, Chan<P, Tx, Rx>), Rx::Error> where S: Session<Action = Recv<T, P>>, P: Session, Rx: Receive<T>, { let result = self.rx.as_mut().unwrap().recv().await?; Ok((result, self.unchecked_cast())) } /// Send something of type `T` on the channel *by value*, returning the channel. /// /// # Errors /// /// This function returns the [`Transmitter::Error`] for the underlying `Tx` connection if there /// was an error while sending. /// /// # Examples /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// let (c1, c2) = <Session! { send String }>::channel(|| mpsc::channel(1)); /// c1.send("Hello, world!".to_string()).await?; /// /// let (s, c2) = c2.recv().await?; /// assert_eq!(s, "Hello, world!"); /// # Ok(()) /// # } /// ``` pub async fn send<T, P>(mut self, message: T) -> Result<Chan<P, Tx, Rx>, Tx::Error> where S: Session<Action = Send<T, P>>, P: Session, Tx: Transmit<T>, T: marker::Send, { self.tx.as_mut().unwrap().send(message).await?; Ok(self.unchecked_cast()) } /// Send something of type `T` on the channel *by reference*, returning the channel. /// /// # Errors /// /// This function returns the [`Transmitter::Error`] for the underlying `Tx` connection if there /// was an error while sending. /// /// # Examples /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// let (c1, c2) = <Session! { send String }>::channel(|| mpsc::channel(1)); /// c1.send_ref(&"Hello, world!".to_string()).await?; /// /// let (s, c2) = c2.recv().await?; /// assert_eq!(s, "Hello, world!"); /// # Ok(()) /// # } /// ``` pub async fn send_ref<T, P>(mut self, message: &T) -> Result<Chan<P, Tx, Rx>, Tx::Error> where S: Session<Action = Send<T, P>>, P: Session, Tx: Transmit<T, Ref>, T: marker::Send, { self.tx.as_mut().unwrap().send(message).await?; Ok(self.unchecked_cast()) } /// Send something of type `T` on the channel *by mutable reference*, returning the channel. /// /// # Errors /// /// This function returns the [`Transmitter::Error`] for the underlying `Tx` connection if there /// was an error while sending. /// /// # Examples /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// let (c1, c2) = <Session! { send String }>::channel(|| mpsc::channel(1)); /// let mut string = "Hello, world!".to_string(); /// c1.send_mut(&mut string).await?; /// /// let (s, c2) = c2.recv().await?; /// assert_eq!(s, "Hello, world!"); /// # Ok(()) /// # } /// ``` pub async fn send_mut<T, P>(mut self, message: &mut T) -> Result<Chan<P, Tx, Rx>, Tx::Error> where S: Session<Action = Send<T, P>>, P: Session, Tx: Transmit<T, Mut>, T: marker::Send, { self.tx.as_mut().unwrap().send(message).await?; Ok(self.unchecked_cast()) } } impl<Tx, Rx, S, Choices, const LENGTH: usize> Chan<S, Tx, Rx> where S: Session<Action = Choose<Choices>>, Choices: Tuple, Choices::AsList: HasLength, <Choices::AsList as HasLength>::Length: ToConstant<AsConstant = Number<LENGTH>>, Tx: Transmitter + marker::Send + 'static, Rx: marker::Send + 'static, { /// Actively choose to enter the `N`th protocol offered via [`offer!`](crate::offer) by the /// other end of the connection, alerting the other party to this choice by sending the number /// `N` over the channel. /// /// The choice `N` is specified as a `const` generic `usize`. /// /// # Errors /// /// This function returns the [`Transmitter::Error`] for the underlying `Tx` connection if there /// was an error while sending the choice. /// /// # Examples /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// type GiveOrTake = Session! { /// choose { /// 0 => send i64, /// 1 => recv String, /// } /// }; /// /// let (c1, c2) = GiveOrTake::channel(|| mpsc::channel(1)); /// /// // Spawn a thread to offer a choice /// let t1 = tokio::spawn(async move { /// offer!(in c2 { /// 0 => { c2.recv().await?; }, /// 1 => { c2.send("Hello!".to_string()).await?; }, /// }); /// Ok::<_, mpsc::Error>(()) /// }); /// /// // Choose to send an integer /// c1.choose::<0>().await?.send(42).await?; /// /// // Wait for the offering thread to finish /// t1.await??; /// # Ok(()) /// # } /// ``` /// /// Attempting to choose an index that's out of bounds results in a compile-time error: /// /// ```compile_fail /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// type OnlyTwoChoices = Choose<(Done, Done)>; /// let (c1, c2) = OnlyTwoChoices::channel(|| mpsc::channel(1)); /// /// // Try to choose something out of range (this doesn't typecheck) /// c1.choose::<2>().await?; /// /// # // Wait for the offering thread to finish /// # t1.await??; /// # Ok(()) /// # } /// ``` pub async fn choose<const N: usize>( mut self, ) -> Result< Chan<<Choices::AsList as Select<<Number<N> as ToUnary>::AsUnary>>::Selected, Tx, Rx>, Tx::Error, > where Number<N>: ToUnary, Choices::AsList: Select<<Number<N> as ToUnary>::AsUnary>, <Choices::AsList as Select<<Number<N> as ToUnary>::AsUnary>>::Selected: Session, { let choice: Choice<LENGTH> = u8::try_from(N) .expect("choices must fit into a byte") .try_into() .expect("type system prevents out of range choice in `choose`"); self.tx.as_mut().unwrap().send_choice(choice).await?; Ok(self.unchecked_cast()) } } impl<Tx, Rx, S, Choices, const LENGTH: usize> Chan<S, Tx, Rx> where S: Session<Action = Offer<Choices>>, Choices: Tuple + 'static, Choices::AsList: HasLength + EachScoped + EachHasDual, <Choices::AsList as HasLength>::Length: ToConstant<AsConstant = Number<LENGTH>>, Z: LessThan<<Choices::AsList as HasLength>::Length>, Tx: marker::Send + 'static, Rx: Receiver + marker::Send + 'static, { /// Offer the choice of one or more protocols to the other party, and wait for them to indicate /// which protocol they'd like to proceed with. Returns a [`Branches`] structure representing /// all the possible channel types which could be returned, which must be eliminated using /// [`case`](Branches::case). /// ///💡 **Where possible, prefer the [`offer!`](crate::offer) macro**. This has the benefit of /// ensuring at compile time that no case is left unhandled; it's also more succinct. /// /// # Errors /// /// This function returns the [`Receiver::Error`] for the underlying `Rx` connection if there /// was an error while receiving. /// /// # Examples /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// type GiveOrTake = Session! { /// choose { /// 0 => send i64, /// 1 => recv String, /// } /// }; /// /// let (c1, c2) = GiveOrTake::channel(|| mpsc::channel(1)); /// /// // Spawn a thread to offer a choice /// let t1 = tokio::spawn(async move { /// match c2.offer().await?.case::<0>() { /// Ok(c2) => { c2.recv().await?; }, /// Err(rest) => match rest.case::<0>() { /// Ok(c2) => { c2.send("Hello!".to_string()).await?; }, /// Err(rest) => rest.empty_case(), /// } /// } /// Ok::<_, mpsc::Error>(()) /// }); /// /// // Choose to send an integer /// c1.choose::<0>().await?.send(42).await?; /// /// // Wait for the offering thread to finish /// t1.await??; /// # Ok(()) /// # } /// ``` /// /// Notice how the handling of cases by manual `match` is harder to read than the equivalent in /// terms of [`offer!`](crate::offer): /// /// ``` /// # use dialectic::prelude::*; /// # use dialectic_tokio_mpsc as mpsc; /// # /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// # type GiveOrTake = Session! { /// # choose { /// # 0 => send i64, /// # 1 => recv String, /// # } /// # }; /// # /// # let (c1, c2) = GiveOrTake::channel(|| mpsc::channel(1)); /// # /// # // Spawn a thread to offer a choice /// # let t1 = tokio::spawn(async move { /// offer!(in c2 { /// 0 => { c2.recv().await?; }, /// 1 => { c2.send("Hello!".to_string()).await?; }, /// }); /// # Ok::<_, mpsc::Error>(()) /// # }); /// # /// # // Choose to send an integer /// # c1.choose::<0>().await?.send(42).await?; /// # /// # // Wait for the offering thread to finish /// # t1.await??; /// # Ok(()) /// # } /// ``` pub async fn offer(self) -> Result<Branches<Choices, Tx, Rx>, Rx::Error> { let (tx, mut rx, drop_tx, drop_rx) = self.unwrap_contents(); let variant = rx.as_mut().unwrap().recv_choice::<LENGTH>().await?.into(); Ok(Branches { variant, tx, rx, drop_tx, drop_rx, protocols: PhantomData, }) } } impl<Tx, Rx, S> Chan<S, Tx, Rx> where S: Session, Tx: marker::Send + 'static, Rx: marker::Send + 'static, { /// Execute the session type `P` as a subroutine in a closure. /// /// This operation takes as input an asynchronous closure that runs a channel for the session /// type `P` to completion and returns either an error `Err` or some result value `T`. The /// result of this (provided that no errors occurred during `P`) is a channel ready to execute /// the session type `Q`. /// /// # Errors /// /// The closure must *finish* the session `P` on the channel given to it and *drop* the finished /// channel before the future returns. If the channel is dropped before completing `P` or is not /// dropped after completing `P`, a [`SessionIncomplete`] error will be returned instead of a /// channel for `Q`. The best way to ensure this error does not occur is to call /// [`close`](Chan::close) on the channel before returning from the future, because this /// statically checks that the session is complete and drops the channel. /// /// Additionally, this function returns an `Err` if the closure returns an `Err`. /// /// # Examples /// /// This can be used to cleanly modularize a session-typed program by splitting it up into /// independent subroutines: /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// let (c1, c2) = <Session! { /// call { send String }; /// send String; /// }>::channel(mpsc::unbounded_channel); /// /// let ((), c1_result) = c1.call(|c| async move { /// let c = c.send("Hello!".to_string()).await?; /// // Because we're done with this subroutine, we can "close" the channel here, but it /// // will remain open to the calling context so it can run the rest of the session: /// c.close(); /// Ok::<_, mpsc::Error>(()) /// }).await?; /// let c1 = c1_result?; /// /// let c1 = c1.send("World!".to_string()).await?; /// c1.close(); /// # Ok(()) /// # } /// ``` /// /// More generally, this construct permits the expression of context-free session types, by /// allowing recursion in the first parameter to [`Call`]. For a demonstration of this, see the /// [`stack` example](https://github.com/boltlabs-inc/dialectic/tree/main/examples). For more /// background on context-free session types, see the paper [*Context-Free Session Type /// Inference*](https://doi.org/10.1145/3229062) by Luca Padovani. When comparing with that /// paper, note that the [`call`](Chan::call) operation is roughly equivalent to the paper's /// `@=` operator, and the [`Call`] type is equivalent to the paper's `;` type operator. pub async fn call<T, E, P, Q, F, Fut>( self, first: F, ) -> Result<(T, Result<Chan<Q, Tx, Rx>, SessionIncomplete<Tx, Rx>>), E> where S: Session<Action = Call<P, Q>>, P: Session, Q: Session, F: FnOnce(Chan<P, Tx, Rx>) -> Fut, Fut: Future<Output = Result<T, E>>, { let (tx, rx, drop_tx, drop_rx) = self.unwrap_contents(); let (result, chan_result) = P::over(tx.unwrap(), rx.unwrap(), first).await; Ok(( result?, chan_result.map(|(tx, rx)| Chan { tx: Some(tx), rx: Some(rx), drop_tx, drop_rx, session: PhantomData, }), )) } /// Split a channel into transmit-only and receive-only ends and manipulate them, potentially /// concurrently, in the given closure. /// /// This is akin to [`call`](Chan::call), except the closure is given *two* [`Chan`]s: one which /// can only do [`Transmit`] operations ([`Send`] and [`Choose`]) and one which can only do /// [`Receive`] operations ([`Recv`] and [`Offer`]). The result of the call to /// [`split`](Chan::split) is a re-unified [`Chan`] ready to execute the session `R`. /// /// # Errors /// /// The closure must *finish* the session for both the send-only and receive-only ends of the /// channel and drop or [`close`](Chan::close) each end *before* the future completes. If either /// end is dropped before finishing its session, or is not closed after finishing its session, a /// [`SessionIncomplete`] error will be returned instead of a finished channel. /// /// # Examples /// /// In this example, both ends of a channel concurrently interact with its split send/receive /// halves. If the underlying channel implementation allows for parallelism, this simultaneous /// interaction can be faster than sequentially sending data back and forth. /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// # #[tokio::main] /// # async fn main() -> Result<(), Box<dyn std::error::Error>> { /// type SendAndRecv = Session! { /// split { /// -> send Vec<usize>, /// <- recv String, /// } /// }; /// /// let (c1, c2) = SendAndRecv::channel(|| mpsc::channel(1)); /// /// // Spawn a thread to simultaneously send a `Vec<usize>` and receive a `String`: /// let t1 = tokio::spawn(async move { /// c1.split(|tx, rx| async move { /// let send_vec = tokio::spawn(async move { /// tx.send(vec![1, 2, 3, 4, 5]).await?; /// Ok::<_, mpsc::Error>(()) /// }); /// let recv_string = tokio::spawn(async move { /// let (string, _) = rx.recv().await?; /// Ok::<_, mpsc::Error>(string) /// }); /// send_vec.await.unwrap()?; /// let string = recv_string.await.unwrap()?; /// Ok::<_, mpsc::Error>(string) /// }).await /// }); /// /// // Simultaneously *receive* a `Vec<usize>` *from*, and *send* a `String` *to*, /// // the task above: /// c2.split(|tx, rx| async move { /// let send_string = tokio::spawn(async move { /// tx.send("Hello!".to_string()).await?; /// Ok::<_, mpsc::Error>(()) /// }); /// let recv_vec = tokio::spawn(async move { /// let (vec, _) = rx.recv().await?; /// Ok::<_, mpsc::Error>(vec) /// }); /// /// // Examine the result values: /// send_string.await??; /// let vec = recv_vec.await??; /// let string = t1.await??.0; /// assert_eq!(vec, &[1, 2, 3, 4, 5]); /// assert_eq!(string, "Hello!"); /// /// Ok::<_, Box<dyn std::error::Error>>(()) /// }).await?; /// # /// # Ok(()) /// # } /// ``` pub async fn split<T, E, P, Q, R, F, Fut>( self, with_parts: F, ) -> Result<(T, Result<Chan<R, Tx, Rx>, SessionIncomplete<Tx, Rx>>), E> where S: Session<Action = Split<P, Q, R>>, P: Session, Q: Session, R: Session, F: FnOnce(Chan<P, Tx, Unavailable>, Chan<Q, Unavailable, Rx>) -> Fut, Fut: Future<Output = Result<T, E>>, { use IncompleteHalf::*; use SessionIncomplete::*; let (tx, rx, drop_tx, drop_rx) = self.unwrap_contents(); let ((result, maybe_rx), maybe_tx) = P::over(tx.unwrap(), Unavailable::default(), |tx_only| async move { Q::over(Unavailable::default(), rx.unwrap(), |rx_only| async move { with_parts(tx_only, rx_only).await }) .await }) .await; // Unpack and repack the resultant tx and rx or SessionIncomplete to eliminate // Available/Unavailable and maximize possible returned things (it's fine to drop the // Unavailable end of something if for some reason you split twice) let maybe_tx_rx: Result<(Tx, Rx), SessionIncomplete<Tx, Rx>> = match ( maybe_tx .map(|(tx, _)| Ok(tx)) .unwrap_or_else(|incomplete| incomplete.into_halves().0), maybe_rx .map(|(_, rx)| Ok(rx)) .unwrap_or_else(|incomplete| incomplete.into_halves().1), ) { (Ok(tx), Ok(rx)) => Ok((tx, rx)), (Ok(tx), Err(Unclosed)) => Err(RxHalf { tx, rx: Unclosed }), (Err(Unclosed), Ok(rx)) => Err(TxHalf { tx: Unclosed, rx }), (Ok(tx), Err(Unfinished(rx))) => Err(RxHalf { tx, rx: Unfinished(rx), }), (Err(Unfinished(tx)), Ok(rx)) => Err(TxHalf { tx: Unfinished(tx), rx, }), (Err(Unfinished(tx)), Err(Unclosed)) => Err(BothHalves { tx: Unfinished(tx), rx: Unclosed, }), (Err(Unclosed), Err(Unfinished(rx))) => Err(BothHalves { tx: Unclosed, rx: Unfinished(rx), }), (Err(Unclosed), Err(Unclosed)) => Err(BothHalves { tx: Unclosed, rx: Unclosed, }), (Err(Unfinished(tx)), Err(Unfinished(rx))) => Err(BothHalves { tx: Unfinished(tx), rx: Unfinished(rx), }), }; Ok(( result?, maybe_tx_rx.map(|(tx, rx)| Chan { tx: Some(tx), rx: Some(rx), drop_tx, drop_rx, session: PhantomData, }), )) } /// Unwrap a channel into its transmit and receive ends, exiting the regimen of session typing, /// potentially before the end of the session. /// /// # Errors /// /// If this function is used before the end of a session, it may result in errors when the other /// end of the channel attempts to continue the session. /// /// # Examples /// /// ``` /// use dialectic::prelude::*; /// use dialectic_tokio_mpsc as mpsc; /// /// let (c1, c2) = <Session! { send String }>::channel(mpsc::unbounded_channel); /// let (tx1, rx1) = c1.into_inner(); /// let (tx2, rx2) = c2.into_inner(); /// ``` pub fn into_inner(self) -> (Tx, Rx) { let (tx, rx, _, _) = self.unwrap_contents(); (tx.unwrap(), rx.unwrap()) } /// Unwrap all the contained data in this `Chan` without returning its destructor. This is only /// useful internally when implementing exposed functions. fn unwrap_contents( mut self, ) -> ( Option<Tx>, Option<Rx>, Arc<Mutex<Result<Tx, IncompleteHalf<Tx>>>>, Arc<Mutex<Result<Rx, IncompleteHalf<Rx>>>>, ) { let tx = self.tx.take(); let rx = self.rx.take(); let drop_tx = self.drop_tx.clone(); let drop_rx = self.drop_rx.clone(); (tx, rx, drop_tx, drop_rx) } /// Cast a channel to arbitrary new session types and environment. Use with care! fn unchecked_cast<Q>(mut self) -> Chan<Q, Tx, Rx> where Q: Session, { // Cast a pointer to `self` to the new desired (phantom) session type let new: *mut Chan<Q, _, _> = (&mut self as *mut Chan<_, _, _>).cast(); // Forget `self` to prevent a double-free error mem::forget(self); // Read the contents of `new` to get the new channel unsafe { new.read() } } /// Create a new channel with an arbitrary environment and session type. This is equivalent to /// casting a new channel to an arbitrary environment, and doesn't guarantee the environment is /// coherent with regard to the session type. Use with care! pub(crate) fn from_raw_unchecked(tx: Tx, rx: Rx) -> Chan<S, Tx, Rx> { Chan { tx: Some(tx), rx: Some(rx), drop_tx: Arc::new(Mutex::new(Err(IncompleteHalf::Unclosed))), drop_rx: Arc::new(Mutex::new(Err(IncompleteHalf::Unclosed))), session: PhantomData, } } } /// The implementation of `Session::over`. This has to be defined here because it uses the internals /// of `Chan`. pub(crate) fn over<P, Tx, Rx, T, F, Fut>(tx: Tx, rx: Rx, with_chan: F) -> Over<Tx, Rx, T, Fut> where P: Session, Tx: std::marker::Send + 'static, Rx: std::marker::Send + 'static, F: FnOnce(Chan<P, Tx, Rx>) -> Fut, Fut: Future<Output = T>, { let drop_tx = Arc::new(Mutex::new(Err(IncompleteHalf::Unclosed))); let drop_rx = Arc::new(Mutex::new(Err(IncompleteHalf::Unclosed))); let reclaimed_tx = drop_tx.clone(); let reclaimed_rx = drop_rx.clone(); let chan = Chan { tx: Some(tx), rx: Some(rx), drop_tx, drop_rx, session: PhantomData, }; Over { future: with_chan(chan), reclaimed_tx, reclaimed_rx, } } impl<Tx, Rx, T, Fut> Future for Over<Tx, Rx, T, Fut> where Fut: Future<Output = T>, { type Output = (T, Result<(Tx, Rx), SessionIncomplete<Tx, Rx>>); fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> { use IncompleteHalf::*; use SessionIncomplete::*; let reclaimed_tx = self.reclaimed_tx.clone(); let reclaimed_rx = self.reclaimed_rx.clone(); self.project().future.poll(cx).map(|result| { let chan = match ( mem::replace(&mut *reclaimed_tx.lock().unwrap(), Err(Unclosed)), mem::replace(&mut *reclaimed_rx.lock().unwrap(), Err(Unclosed)), ) { (Ok(tx), Ok(rx)) => Ok((tx, rx)), (Err(tx), Ok(rx)) => Err(TxHalf { tx, rx }), (Ok(tx), Err(rx)) => Err(RxHalf { tx, rx }), (Err(tx), Err(rx)) => Err(BothHalves { tx, rx }), }; (result, chan) }) } } /// The future returned by [`Session::over`] (see its documentation for details). #[pin_project] #[derive(Debug)] pub struct Over<Tx, Rx, T, Fut> where Fut: Future<Output = T>, { /// The destination for the reclaimed transmit half after drop. reclaimed_tx: Arc<Mutex<Result<Tx, IncompleteHalf<Tx>>>>, /// The destination for the reclaimed receive half after drop. reclaimed_rx: Arc<Mutex<Result<Rx, IncompleteHalf<Rx>>>>, /// The wrapped future itself. #[pin] future: Fut, } /// The result of [`offer`](Chan::offer): an `N`-ary enumeration of the possible [`Chan`]s that /// could result from the what the other party [`choose`](Chan::choose)s. /// /// To find out which protocol was selected by the other party, use [`Branches::case`] (the analogue /// to a `match` statement on [`Branches`]). /// /// **💡 When possible, prefer the [`offer!`] macro over using [`Branches`] and /// [`case`](Branches::case).** It guarantees exhaustiveness, and is more concise, readable, and /// asymptotically efficient. #[derive(Derivative)] #[derivative(Debug)] #[must_use] pub struct Branches<Choices, Tx, Rx> where Tx: marker::Send + 'static, Rx: marker::Send + 'static, Choices: Tuple + 'static, Choices::AsList: EachScoped + EachHasDual + HasLength, { variant: u8, tx: Option<Tx>, rx: Option<Rx>, drop_tx: Arc<Mutex<Result<Tx, IncompleteHalf<Tx>>>>, drop_rx: Arc<Mutex<Result<Rx, IncompleteHalf<Rx>>>>, protocols: PhantomData<fn() -> Choices>, } impl<Tx, Rx, Choices> Drop for Branches<Choices, Tx, Rx> where Tx: marker::Send + 'static, Rx: marker::Send + 'static, Choices: Tuple + 'static, Choices::AsList: EachScoped + EachHasDual + HasLength, { fn drop(&mut self) { if let Some(tx) = self.tx.take() { *self.drop_tx.lock().unwrap() = Err(IncompleteHalf::Unfinished(tx)); } if let Some(rx) = self.rx.take() { *self.drop_rx.lock().unwrap() = Err(IncompleteHalf::Unfinished(rx)); } } } impl<Tx, Rx, Choices, const LENGTH: usize> Branches<Choices, Tx, Rx> where Choices: Tuple + 'static, Choices::AsList: EachScoped + EachHasDual + HasLength, <Choices::AsList as HasLength>::Length: ToConstant<AsConstant = Number<LENGTH>>, Tx: marker::Send + 'static, Rx: marker::Send + 'static, { /// Check if the selected protocol in this [`Branches`] was the `N`th protocol in its type. If /// so, return the corresponding channel; otherwise, return all the other possibilities. pub fn case<const N: usize>( mut self, ) -> Result< Chan<<Choices::AsList as Select<<Number<N> as ToUnary>::AsUnary>>::Selected, Tx, Rx>, Branches<<<Choices::AsList as Select<<Number<N> as ToUnary>::AsUnary>>::Remainder as List>::AsTuple, Tx, Rx>, > where Number<N>: ToUnary, Choices::AsList: Select<<Number<N> as ToUnary>::AsUnary>, <Choices::AsList as Select<<Number<N> as ToUnary>::AsUnary>>::Selected: Session, <Choices::AsList as Select<<Number<N> as ToUnary>::AsUnary>>::Remainder: EachScoped + EachHasDual + HasLength + List, { let variant = self.variant; let tx = self.tx.take(); let rx = self.rx.take(); let drop_tx = self.drop_tx.clone(); let drop_rx = self.drop_rx.clone(); let branch: u8 = N .try_into() .expect("branch discriminant exceeded u8::MAX in `case`"); if variant == branch { Ok(Chan { tx, rx, drop_tx, drop_rx, session: PhantomData, }) } else { Err(Branches { // Subtract 1 from variant if we've eliminated a branch with a lower discriminant variant: if variant > branch { variant - 1 } else { variant }, tx, rx, drop_tx, drop_rx, protocols: PhantomData, }) } } /// Determine the [`Choice`] which was made by the other party, indicating which of these /// [`Branches`] should be taken. /// /// Ordinarily, you should prefer the [`offer!`](crate::offer) macro in situations where you /// need to know this value. pub fn choice(&self) -> Choice<LENGTH> { self.variant .try_into() .expect("internal variant for `Branches` exceeds number of choices") } } impl<'a, Tx, Rx> Branches<(), Tx, Rx> where Tx: marker::Send + 'static, Rx: marker::Send + 'static, { /// Eliminate an empty [`Branches`], returning any type. Any code in which this function can be /// called is unreachable, because it's impossible to construct an empty [`Branches`]. pub fn empty_case<T>(self) -> T { unreachable!("empty `Branches` cannot be constructed") } }