Move embassy-net-driver-channel::zerocopy_channel to embassy_sync::zero_copy_channel

2 files changed, 210 insertions, 0 deletions

diff --git a/embassy-sync/src/lib.rs b/embassy-sync/src/lib.rs
index 53d95d081..48a7b13f6 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 zero_copy_channel;
diff --git a/embassy-sync/src/zero_copy_channel.rs b/embassy-sync/src/zero_copy_channel.rs
new file mode 100644
index 000000000..3701ccf1a
--- /dev/null
+++ b/embassy-sync/src/zero_copy_channel.rs
@@ -0,0 +1,209 @@
+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;
+
+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();
+    }
+}