Merge pull request #1771 from rubdos/zero-copy-channel

embassy_sync::zero_copy_channel

3 files changed, 273 insertions, 223 deletions

diff --git a/embassy-net-driver-channel/src/lib.rs b/embassy-net-driver-channel/src/lib.rs
index f2aa6b254..bf7ae5217 100644
--- a/embassy-net-driver-channel/src/lib.rs
+++ b/embassy-net-driver-channel/src/lib.rs
@@ -14,6 +14,7 @@ use embassy_net_driver::{Capabilities, LinkState, Medium};
 use embassy_sync::blocking_mutex::raw::NoopRawMutex;
 use embassy_sync::blocking_mutex::Mutex;
 use embassy_sync::waitqueue::WakerRegistration;
+use embassy_sync::zerocopy_channel;
 
 pub struct State<const MTU: usize, const N_RX: usize, const N_TX: usize> {
     rx: [PacketBuf<MTU>; N_RX],
@@ -130,24 +131,24 @@ impl<'d, const MTU: usize> Runner<'d, MTU> {
     }
 
     pub async fn tx_buf(&mut self) -> &mut [u8] {
-        let p = self.tx_chan.recv().await;
+        let p = self.tx_chan.receive().await;
         &mut p.buf[..p.len]
     }
 
     pub fn try_tx_buf(&mut self) -> Option<&mut [u8]> {
-        let p = self.tx_chan.try_recv()?;
+        let p = self.tx_chan.try_receive()?;
         Some(&mut p.buf[..p.len])
     }
 
     pub fn poll_tx_buf(&mut self, cx: &mut Context) -> Poll<&mut [u8]> {
-        match self.tx_chan.poll_recv(cx) {
+        match self.tx_chan.poll_receive(cx) {
             Poll::Ready(p) => Poll::Ready(&mut p.buf[..p.len]),
             Poll::Pending => Poll::Pending,
         }
     }
 
     pub fn tx_done(&mut self) {
-        self.tx_chan.recv_done();
+        self.tx_chan.receive_done();
     }
 }
 
@@ -204,24 +205,24 @@ impl<'d, const MTU: usize> RxRunner<'d, MTU> {
 
 impl<'d, const MTU: usize> TxRunner<'d, MTU> {
     pub async fn tx_buf(&mut self) -> &mut [u8] {
-        let p = self.tx_chan.recv().await;
+        let p = self.tx_chan.receive().await;
         &mut p.buf[..p.len]
     }
 
     pub fn try_tx_buf(&mut self) -> Option<&mut [u8]> {
-        let p = self.tx_chan.try_recv()?;
+        let p = self.tx_chan.try_receive()?;
         Some(&mut p.buf[..p.len])
     }
 
     pub fn poll_tx_buf(&mut self, cx: &mut Context) -> Poll<&mut [u8]> {
-        match self.tx_chan.poll_recv(cx) {
+        match self.tx_chan.poll_receive(cx) {
             Poll::Ready(p) => Poll::Ready(&mut p.buf[..p.len]),
             Poll::Pending => Poll::Pending,
         }
     }
 
     pub fn tx_done(&mut self) {
-        self.tx_chan.recv_done();
+        self.tx_chan.receive_done();
     }
 }
 
@@ -293,7 +294,7 @@ impl<'d, const MTU: usize> embassy_net_driver::Driver for Device<'d, MTU> {
     type TxToken<'a> = TxToken<'a, MTU> where Self: 'a ;
 
     fn receive(&mut self, cx: &mut Context) -> Option<(Self::RxToken<'_>, Self::TxToken<'_>)> {
-        if self.rx.poll_recv(cx).is_ready() && self.tx.poll_send(cx).is_ready() {
+        if self.rx.poll_receive(cx).is_ready() && self.tx.poll_send(cx).is_ready() {
             Some((RxToken { rx: self.rx.borrow() }, TxToken { tx: self.tx.borrow() }))
         } else {
             None
@@ -337,9 +338,9 @@ impl<'a, const MTU: usize> embassy_net_driver::RxToken for RxToken<'a, MTU> {
         F: FnOnce(&mut [u8]) -> R,
     {
         // NOTE(unwrap): we checked the queue wasn't full when creating the token.
-        let pkt = unwrap!(self.rx.try_recv());
+        let pkt = unwrap!(self.rx.try_receive());
         let r = f(&mut pkt.buf[..pkt.len]);
-        self.rx.recv_done();
+        self.rx.receive_done();
         r
     }
 }
@@ -361,215 +362,3 @@ impl<'a, const MTU: usize> embassy_net_driver::TxToken for TxToken<'a, MTU> {
         r
     }
 }
-
-mod zerocopy_channel {
-    use core::cell::RefCell;
-    use core::future::poll_fn;
-    use core::marker::PhantomData;
-    use core::task::{Context, Poll};
-
-    use embassy_sync::blocking_mutex::raw::RawMutex;
-    use embassy_sync::blocking_mutex::Mutex;
-    use embassy_sync::waitqueue::WakerRegistration;
-
-    pub struct Channel<'a, M: RawMutex, T> {
-        buf: *mut T,
-        phantom: PhantomData<&'a mut T>,
-        state: Mutex<M, RefCell<State>>,
-    }
-
-    impl<'a, M: RawMutex, T> Channel<'a, M, T> {
-        pub fn new(buf: &'a mut [T]) -> Self {
-            let len = buf.len();
-            assert!(len != 0);
-
-            Self {
-                buf: buf.as_mut_ptr(),
-                phantom: PhantomData,
-                state: Mutex::new(RefCell::new(State {
-                    len,
-                    front: 0,
-                    back: 0,
-                    full: false,
-                    send_waker: WakerRegistration::new(),
-                    recv_waker: WakerRegistration::new(),
-                })),
-            }
-        }
-
-        pub fn split(&mut self) -> (Sender<'_, M, T>, Receiver<'_, M, T>) {
-            (Sender { channel: self }, Receiver { channel: self })
-        }
-    }
-
-    pub struct Sender<'a, M: RawMutex, T> {
-        channel: &'a Channel<'a, M, T>,
-    }
-
-    impl<'a, M: RawMutex, T> Sender<'a, M, T> {
-        pub fn borrow(&mut self) -> Sender<'_, M, T> {
-            Sender { channel: self.channel }
-        }
-
-        pub fn try_send(&mut self) -> Option<&mut T> {
-            self.channel.state.lock(|s| {
-                let s = &mut *s.borrow_mut();
-                match s.push_index() {
-                    Some(i) => Some(unsafe { &mut *self.channel.buf.add(i) }),
-                    None => None,
-                }
-            })
-        }
-
-        pub fn poll_send(&mut self, cx: &mut Context) -> Poll<&mut T> {
-            self.channel.state.lock(|s| {
-                let s = &mut *s.borrow_mut();
-                match s.push_index() {
-                    Some(i) => Poll::Ready(unsafe { &mut *self.channel.buf.add(i) }),
-                    None => {
-                        s.recv_waker.register(cx.waker());
-                        Poll::Pending
-                    }
-                }
-            })
-        }
-
-        pub async fn send(&mut self) -> &mut T {
-            let i = poll_fn(|cx| {
-                self.channel.state.lock(|s| {
-                    let s = &mut *s.borrow_mut();
-                    match s.push_index() {
-                        Some(i) => Poll::Ready(i),
-                        None => {
-                            s.recv_waker.register(cx.waker());
-                            Poll::Pending
-                        }
-                    }
-                })
-            })
-            .await;
-            unsafe { &mut *self.channel.buf.add(i) }
-        }
-
-        pub fn send_done(&mut self) {
-            self.channel.state.lock(|s| s.borrow_mut().push_done())
-        }
-    }
-    pub struct Receiver<'a, M: RawMutex, T> {
-        channel: &'a Channel<'a, M, T>,
-    }
-
-    impl<'a, M: RawMutex, T> Receiver<'a, M, T> {
-        pub fn borrow(&mut self) -> Receiver<'_, M, T> {
-            Receiver { channel: self.channel }
-        }
-
-        pub fn try_recv(&mut self) -> Option<&mut T> {
-            self.channel.state.lock(|s| {
-                let s = &mut *s.borrow_mut();
-                match s.pop_index() {
-                    Some(i) => Some(unsafe { &mut *self.channel.buf.add(i) }),
-                    None => None,
-                }
-            })
-        }
-
-        pub fn poll_recv(&mut self, cx: &mut Context) -> Poll<&mut T> {
-            self.channel.state.lock(|s| {
-                let s = &mut *s.borrow_mut();
-                match s.pop_index() {
-                    Some(i) => Poll::Ready(unsafe { &mut *self.channel.buf.add(i) }),
-                    None => {
-                        s.send_waker.register(cx.waker());
-                        Poll::Pending
-                    }
-                }
-            })
-        }
-
-        pub async fn recv(&mut self) -> &mut T {
-            let i = poll_fn(|cx| {
-                self.channel.state.lock(|s| {
-                    let s = &mut *s.borrow_mut();
-                    match s.pop_index() {
-                        Some(i) => Poll::Ready(i),
-                        None => {
-                            s.send_waker.register(cx.waker());
-                            Poll::Pending
-                        }
-                    }
-                })
-            })
-            .await;
-            unsafe { &mut *self.channel.buf.add(i) }
-        }
-
-        pub fn recv_done(&mut self) {
-            self.channel.state.lock(|s| s.borrow_mut().pop_done())
-        }
-    }
-
-    struct State {
-        len: usize,
-
-        /// Front index. Always 0..=(N-1)
-        front: usize,
-        /// Back index. Always 0..=(N-1).
-        back: usize,
-
-        /// Used to distinguish "empty" and "full" cases when `front == back`.
-        /// May only be `true` if `front == back`, always `false` otherwise.
-        full: bool,
-
-        send_waker: WakerRegistration,
-        recv_waker: WakerRegistration,
-    }
-
-    impl State {
-        fn increment(&self, i: usize) -> usize {
-            if i + 1 == self.len {
-                0
-            } else {
-                i + 1
-            }
-        }
-
-        fn is_full(&self) -> bool {
-            self.full
-        }
-
-        fn is_empty(&self) -> bool {
-            self.front == self.back && !self.full
-        }
-
-        fn push_index(&mut self) -> Option<usize> {
-            match self.is_full() {
-                true => None,
-                false => Some(self.back),
-            }
-        }
-
-        fn push_done(&mut self) {
-            assert!(!self.is_full());
-            self.back = self.increment(self.back);
-            if self.back == self.front {
-                self.full = true;
-            }
-            self.send_waker.wake();
-        }
-
-        fn pop_index(&mut self) -> Option<usize> {
-            match self.is_empty() {
-                true => None,
-                false => Some(self.front),
-            }
-        }
-
-        fn pop_done(&mut self) {
-            assert!(!self.is_empty());
-            self.front = self.increment(self.front);
-            self.full = false;
-            self.recv_waker.wake();
-        }
-    }
-}
diff --git a/embassy-sync/src/lib.rs b/embassy-sync/src/lib.rs
index 53d95d081..8a9f841ee 100644
--- a/embassy-sync/src/lib.rs
+++ b/embassy-sync/src/lib.rs
@@ -17,3 +17,4 @@ pub mod pipe;
 pub mod pubsub;
 pub mod signal;
 pub mod waitqueue;
+pub mod zerocopy_channel;
diff --git a/embassy-sync/src/zerocopy_channel.rs b/embassy-sync/src/zerocopy_channel.rs
new file mode 100644
index 000000000..f704cbd5d
--- /dev/null
+++ b/embassy-sync/src/zerocopy_channel.rs
@@ -0,0 +1,260 @@
+//! A zero-copy queue for sending values between asynchronous tasks.
+//!
+//! It can be used concurrently by multiple producers (senders) and multiple
+//! consumers (receivers), i.e. it is an  "MPMC channel".
+//!
+//! Receivers are competing for messages. So a message that is received by
+//! one receiver is not received by any other.
+//!
+//! This queue takes a Mutex type so that various
+//! targets can be attained. For example, a ThreadModeMutex can be used
+//! for single-core Cortex-M targets where messages are only passed
+//! between tasks running in thread mode. Similarly, a CriticalSectionMutex
+//! can also be used for single-core targets where messages are to be
+//! passed from exception mode e.g. out of an interrupt handler.
+//!
+//! This module provides a bounded channel that has a limit on the number of
+//! messages that it can store, and if this limit is reached, trying to send
+//! another message will result in an error being returned.
+
+use core::cell::RefCell;
+use core::future::poll_fn;
+use core::marker::PhantomData;
+use core::task::{Context, Poll};
+
+use crate::blocking_mutex::raw::RawMutex;
+use crate::blocking_mutex::Mutex;
+use crate::waitqueue::WakerRegistration;
+
+/// A bounded zero-copy channel for communicating between asynchronous tasks
+/// with backpressure.
+///
+/// The channel will buffer up to the provided number of messages.  Once the
+/// buffer is full, attempts to `send` new messages will wait until a message is
+/// received from the channel.
+///
+/// All data sent will become available in the same order as it was sent.
+///
+/// The channel requires a buffer of recyclable elements.  Writing to the channel is done through
+/// an `&mut T`.
+pub struct Channel<'a, M: RawMutex, T> {
+    buf: *mut T,
+    phantom: PhantomData<&'a mut T>,
+    state: Mutex<M, RefCell<State>>,
+}
+
+impl<'a, M: RawMutex, T> Channel<'a, M, T> {
+    /// Initialize a new [`Channel`].
+    ///
+    /// The provided buffer will be used and reused by the channel's logic, and thus dictates the
+    /// channel's capacity.
+    pub fn new(buf: &'a mut [T]) -> Self {
+        let len = buf.len();
+        assert!(len != 0);
+
+        Self {
+            buf: buf.as_mut_ptr(),
+            phantom: PhantomData,
+            state: Mutex::new(RefCell::new(State {
+                len,
+                front: 0,
+                back: 0,
+                full: false,
+                send_waker: WakerRegistration::new(),
+                receive_waker: WakerRegistration::new(),
+            })),
+        }
+    }
+
+    /// Creates a [`Sender`] and [`Receiver`] from an existing channel.
+    ///
+    /// Further Senders and Receivers can be created through [`Sender::borrow`] and
+    /// [`Receiver::borrow`] respectively.
+    pub fn split(&mut self) -> (Sender<'_, M, T>, Receiver<'_, M, T>) {
+        (Sender { channel: self }, Receiver { channel: self })
+    }
+}
+
+/// Send-only access to a [`Channel`].
+pub struct Sender<'a, M: RawMutex, T> {
+    channel: &'a Channel<'a, M, T>,
+}
+
+impl<'a, M: RawMutex, T> Sender<'a, M, T> {
+    /// Creates one further [`Sender`] over the same channel.
+    pub fn borrow(&mut self) -> Sender<'_, M, T> {
+        Sender { channel: self.channel }
+    }
+
+    /// Attempts to send a value over the channel.
+    pub fn try_send(&mut self) -> Option<&mut T> {
+        self.channel.state.lock(|s| {
+            let s = &mut *s.borrow_mut();
+            match s.push_index() {
+                Some(i) => Some(unsafe { &mut *self.channel.buf.add(i) }),
+                None => None,
+            }
+        })
+    }
+
+    /// Attempts to send a value over the channel.
+    pub fn poll_send(&mut self, cx: &mut Context) -> Poll<&mut T> {
+        self.channel.state.lock(|s| {
+            let s = &mut *s.borrow_mut();
+            match s.push_index() {
+                Some(i) => Poll::Ready(unsafe { &mut *self.channel.buf.add(i) }),
+                None => {
+                    s.receive_waker.register(cx.waker());
+                    Poll::Pending
+                }
+            }
+        })
+    }
+
+    /// Asynchronously send a value over the channel.
+    pub async fn send(&mut self) -> &mut T {
+        let i = poll_fn(|cx| {
+            self.channel.state.lock(|s| {
+                let s = &mut *s.borrow_mut();
+                match s.push_index() {
+                    Some(i) => Poll::Ready(i),
+                    None => {
+                        s.receive_waker.register(cx.waker());
+                        Poll::Pending
+                    }
+                }
+            })
+        })
+        .await;
+        unsafe { &mut *self.channel.buf.add(i) }
+    }
+
+    /// Notify the channel that the sending of the value has been finalized.
+    pub fn send_done(&mut self) {
+        self.channel.state.lock(|s| s.borrow_mut().push_done())
+    }
+}
+
+/// Receive-only access to a [`Channel`].
+pub struct Receiver<'a, M: RawMutex, T> {
+    channel: &'a Channel<'a, M, T>,
+}
+
+impl<'a, M: RawMutex, T> Receiver<'a, M, T> {
+    /// Creates one further [`Sender`] over the same channel.
+    pub fn borrow(&mut self) -> Receiver<'_, M, T> {
+        Receiver { channel: self.channel }
+    }
+
+    /// Attempts to receive a value over the channel.
+    pub fn try_receive(&mut self) -> Option<&mut T> {
+        self.channel.state.lock(|s| {
+            let s = &mut *s.borrow_mut();
+            match s.pop_index() {
+                Some(i) => Some(unsafe { &mut *self.channel.buf.add(i) }),
+                None => None,
+            }
+        })
+    }
+
+    /// Attempts to asynchronously receive a value over the channel.
+    pub fn poll_receive(&mut self, cx: &mut Context) -> Poll<&mut T> {
+        self.channel.state.lock(|s| {
+            let s = &mut *s.borrow_mut();
+            match s.pop_index() {
+                Some(i) => Poll::Ready(unsafe { &mut *self.channel.buf.add(i) }),
+                None => {
+                    s.send_waker.register(cx.waker());
+                    Poll::Pending
+                }
+            }
+        })
+    }
+
+    /// Asynchronously receive a value over the channel.
+    pub async fn receive(&mut self) -> &mut T {
+        let i = poll_fn(|cx| {
+            self.channel.state.lock(|s| {
+                let s = &mut *s.borrow_mut();
+                match s.pop_index() {
+                    Some(i) => Poll::Ready(i),
+                    None => {
+                        s.send_waker.register(cx.waker());
+                        Poll::Pending
+                    }
+                }
+            })
+        })
+        .await;
+        unsafe { &mut *self.channel.buf.add(i) }
+    }
+
+    /// Notify the channel that the receiving of the value has been finalized.
+    pub fn receive_done(&mut self) {
+        self.channel.state.lock(|s| s.borrow_mut().pop_done())
+    }
+}
+
+struct State {
+    len: usize,
+
+    /// Front index. Always 0..=(N-1)
+    front: usize,
+    /// Back index. Always 0..=(N-1).
+    back: usize,
+
+    /// Used to distinguish "empty" and "full" cases when `front == back`.
+    /// May only be `true` if `front == back`, always `false` otherwise.
+    full: bool,
+
+    send_waker: WakerRegistration,
+    receive_waker: WakerRegistration,
+}
+
+impl State {
+    fn increment(&self, i: usize) -> usize {
+        if i + 1 == self.len {
+            0
+        } else {
+            i + 1
+        }
+    }
+
+    fn is_full(&self) -> bool {
+        self.full
+    }
+
+    fn is_empty(&self) -> bool {
+        self.front == self.back && !self.full
+    }
+
+    fn push_index(&mut self) -> Option<usize> {
+        match self.is_full() {
+            true => None,
+            false => Some(self.back),
+        }
+    }
+
+    fn push_done(&mut self) {
+        assert!(!self.is_full());
+        self.back = self.increment(self.back);
+        if self.back == self.front {
+            self.full = true;
+        }
+        self.send_waker.wake();
+    }
+
+    fn pop_index(&mut self) -> Option<usize> {
+        match self.is_empty() {
+            true => None,
+            false => Some(self.front),
+        }
+    }
+
+    fn pop_done(&mut self) {
+        assert!(!self.is_empty());
+        self.front = self.increment(self.front);
+        self.full = false;
+        self.receive_waker.wake();
+    }
+}