use std::cell::{RefCell, UnsafeCell};
use std::fmt;
use std::future::Future;
use std::mem::MaybeUninit;
use std::pin::Pin;
use std::rc::Rc;
use std::task::Poll::{Pending, Ready};
use std::task::{Context, Poll, Waker};
#[derive(Debug)]
pub struct Sender<T> {
inner: Option<Rc<Inner<T>>>,
}
#[derive(Debug)]
pub struct Receiver<T> {
inner: Option<Rc<Inner<T>>>,
}
pub mod error {
use std::fmt;
#[derive(Debug, Eq, PartialEq)]
pub struct RecvError(pub(super) ());
#[derive(Debug, Eq, PartialEq)]
pub enum TryRecvError {
Empty,
Closed,
}
impl fmt::Display for RecvError {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(fmt, "channel closed")
}
}
impl std::error::Error for RecvError {}
impl fmt::Display for TryRecvError {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
TryRecvError::Empty => write!(fmt, "channel empty"),
TryRecvError::Closed => write!(fmt, "channel closed"),
}
}
}
impl std::error::Error for TryRecvError {}
}
use futures_core::ready;
use self::error::*;
struct Inner<T> {
state: RefCell<usize>,
value: UnsafeCell<Option<T>>,
tx_task: Task,
rx_task: Task,
}
struct Task(UnsafeCell<MaybeUninit<Waker>>);
impl Task {
unsafe fn will_wake(&self, cx: &mut Context<'_>) -> bool {
self.with_task(|w| w.will_wake(cx.waker()))
}
unsafe fn with_task<F, R>(&self, f: F) -> R
where
F: FnOnce(&Waker) -> R,
{
let ptr = self.0.get();
let waker: *const Waker = (&*ptr).as_ptr();
f(&*waker)
}
unsafe fn drop_task(&self) {
let ptr: *mut Waker = (&mut *self.0.get()).as_mut_ptr();
ptr.drop_in_place();
}
unsafe fn set_task(&self, cx: &mut Context<'_>) {
let ptr: *mut Waker = (&mut *self.0.get()).as_mut_ptr();
ptr.write(cx.waker().clone());
}
}
#[derive(Clone, Copy)]
struct State(usize);
pub fn channel<T>() -> (Sender<T>, Receiver<T>) {
let inner = Rc::new(Inner {
state: RefCell::new(State::new().as_usize()),
value: UnsafeCell::new(None),
tx_task: Task(UnsafeCell::new(MaybeUninit::uninit())),
rx_task: Task(UnsafeCell::new(MaybeUninit::uninit())),
});
let tx = Sender {
inner: Some(inner.clone()),
};
let rx = Receiver { inner: Some(inner) };
(tx, rx)
}
impl<T> Sender<T> {
pub fn send(mut self, t: T) -> Result<(), T> {
let inner = self.inner.take().unwrap();
let ptr = inner.value.get();
unsafe {
*ptr = Some(t);
}
if !inner.complete() {
unsafe {
return Err(inner.consume_value().unwrap());
}
}
Ok(())
}
pub async fn closed(&mut self) {
use futures_util::future::poll_fn;
poll_fn(|cx| self.poll_closed(cx)).await
}
pub fn is_closed(&self) -> bool {
let inner = self.inner.as_ref().unwrap();
let state = State(*inner.state.borrow());
state.is_closed()
}
pub fn poll_closed(&mut self, cx: &mut Context<'_>) -> Poll<()> {
let inner = self.inner.as_ref().unwrap();
let mut state = State(*inner.state.borrow());
if state.is_closed() {
return Poll::Ready(());
}
if state.is_tx_task_set() {
let will_notify = unsafe { inner.tx_task.will_wake(cx) };
if !will_notify {
state = State::unset_tx_task(&inner.state);
if state.is_closed() {
State::set_tx_task(&inner.state);
return Ready(());
} else {
unsafe { inner.tx_task.drop_task() };
}
}
}
if !state.is_tx_task_set() {
unsafe {
inner.tx_task.set_task(cx);
}
state = State::set_tx_task(&inner.state);
if state.is_closed() {
return Ready(());
}
}
Pending
}
}
impl<T> Drop for Sender<T> {
fn drop(&mut self) {
if let Some(inner) = self.inner.as_ref() {
inner.complete();
}
}
}
impl<T> Receiver<T> {
pub fn close(&mut self) {
if let Some(inner) = self.inner.as_ref() {
inner.close();
}
}
pub fn try_recv(&mut self) -> Result<T, TryRecvError> {
let result = if let Some(inner) = self.inner.as_ref() {
let state = State(*inner.state.borrow());
if state.is_complete() {
match unsafe { inner.consume_value() } {
Some(value) => Ok(value),
None => Err(TryRecvError::Closed),
}
} else if state.is_closed() {
Err(TryRecvError::Closed)
} else {
return Err(TryRecvError::Empty);
}
} else {
Err(TryRecvError::Closed)
};
self.inner = None;
result
}
}
impl<T> Drop for Receiver<T> {
fn drop(&mut self) {
if let Some(inner) = self.inner.as_ref() {
inner.close();
}
}
}
impl<T> Future for Receiver<T> {
type Output = Result<T, RecvError>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let ret = if let Some(inner) = self.as_ref().get_ref().inner.as_ref() {
ready!(inner.poll_recv(cx))?
} else {
panic!("called after complete");
};
self.inner = None;
Ready(Ok(ret))
}
}
impl<T> Inner<T> {
fn complete(&self) -> bool {
let prev = State::set_complete(&self.state);
if prev.is_closed() {
return false;
}
if prev.is_rx_task_set() {
unsafe {
self.rx_task.with_task(Waker::wake_by_ref);
}
}
true
}
fn poll_recv(&self, cx: &mut Context<'_>) -> Poll<Result<T, RecvError>> {
let mut state = State(*self.state.borrow());
if state.is_complete() {
match unsafe { self.consume_value() } {
Some(value) => Ready(Ok(value)),
None => Ready(Err(RecvError(()))),
}
} else if state.is_closed() {
Ready(Err(RecvError(())))
} else {
if state.is_rx_task_set() {
let will_notify = unsafe { self.rx_task.will_wake(cx) };
if !will_notify {
state = State::unset_rx_task(&self.state);
if state.is_complete() {
State::set_rx_task(&self.state);
return match unsafe { self.consume_value() } {
Some(value) => Ready(Ok(value)),
None => Ready(Err(RecvError(()))),
};
} else {
unsafe { self.rx_task.drop_task() };
}
}
}
if !state.is_rx_task_set() {
unsafe {
self.rx_task.set_task(cx);
}
state = State::set_rx_task(&self.state);
if state.is_complete() {
match unsafe { self.consume_value() } {
Some(value) => Ready(Ok(value)),
None => Ready(Err(RecvError(()))),
}
} else {
Pending
}
} else {
Pending
}
}
}
fn close(&self) {
let prev = State::set_closed(&self.state);
if prev.is_tx_task_set() && !prev.is_complete() {
unsafe {
self.tx_task.with_task(Waker::wake_by_ref);
}
}
}
unsafe fn consume_value(&self) -> Option<T> {
let ptr = self.value.get();
(*ptr).take()
}
}
impl<T> Drop for Inner<T> {
fn drop(&mut self) {
let state = State(*self.state.borrow());
if state.is_rx_task_set() {
unsafe {
self.rx_task.drop_task();
}
}
if state.is_tx_task_set() {
unsafe {
self.tx_task.drop_task();
}
}
}
}
impl<T: fmt::Debug> fmt::Debug for Inner<T> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("Inner")
.field("state", &self.state.borrow())
.finish()
}
}
const RX_TASK_SET: usize = 0b00001;
const VALUE_SENT: usize = 0b00010;
const CLOSED: usize = 0b00100;
const TX_TASK_SET: usize = 0b01000;
impl State {
fn new() -> State {
State(0)
}
fn is_complete(self) -> bool {
self.0 & VALUE_SENT == VALUE_SENT
}
fn set_complete(cell: &RefCell<usize>) -> State {
let mut val = cell.borrow_mut();
*val |= VALUE_SENT;
State(*val)
}
fn is_rx_task_set(self) -> bool {
self.0 & RX_TASK_SET == RX_TASK_SET
}
fn set_rx_task(cell: &RefCell<usize>) -> State {
let mut val = cell.borrow_mut();
*val |= RX_TASK_SET;
State(*val)
}
fn unset_rx_task(cell: &RefCell<usize>) -> State {
let mut val = cell.borrow_mut();
*val &= !RX_TASK_SET;
State(*val)
}
fn is_closed(self) -> bool {
self.0 & CLOSED == CLOSED
}
fn set_closed(cell: &RefCell<usize>) -> State {
let mut val = cell.borrow_mut();
*val |= CLOSED;
State(*val)
}
fn set_tx_task(cell: &RefCell<usize>) -> State {
let mut val = cell.borrow_mut();
*val |= TX_TASK_SET;
State(*val)
}
fn unset_tx_task(cell: &RefCell<usize>) -> State {
let mut val = cell.borrow_mut();
*val &= !TX_TASK_SET;
State(*val)
}
fn is_tx_task_set(self) -> bool {
self.0 & TX_TASK_SET == TX_TASK_SET
}
fn as_usize(self) -> usize {
self.0
}
}
impl fmt::Debug for State {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("State")
.field("is_complete", &self.is_complete())
.field("is_closed", &self.is_closed())
.field("is_rx_task_set", &self.is_rx_task_set())
.field("is_tx_task_set", &self.is_tx_task_set())
.finish()
}
}
#[cfg(test)]
mod tests {
use super::channel;
#[monoio::test]
async fn it_works() {
let (tx, rx) = channel();
let join = monoio::spawn(async move { rx.await });
tx.send(1).unwrap();
assert_eq!(join.await.unwrap(), 1);
}
}