🔥 ✨ RefCell-less, two-phase update system [wip]

stackline/src/context.rs

@@ -0,0 +1,167 @@
+use std::marker::PhantomData;
+use std::rc::Rc;
+use super::*;
+
+/// An UpdateContext is created for every tile update during the "update" phase,
+/// and it contains the necessary data for a tile to update its internal state.
+///
+/// During the update phase, a tile may only access itself mutably, through the mutable
+/// reference it was initially passed through its [`update`](Tile::update) method.
+/// All accesses to other tiles and all signals must be done immutably.
+///
+/// It thus *cannot* access itself through this context structure, although it may read its
+/// signal here.
+/// It *can* access the other tiles and their signals immutably.
+
+// SAFETY: `pane[position].cell` is borrow mutably, while a pointer to the original Pane is kept;
+// thus, no other reference to `pane[position].cell` may be done
+pub struct UpdateContext<'a> {
+    pub position: (usize, usize),
+    pane: *const Pane,
+
+    phantom: PhantomData<&'a Pane>,
+}
+
+impl<'a> UpdateContext<'a> {
+    #[inline]
+    pub(crate) fn new(pane: &'a mut Pane, position: (usize, usize)) -> Option<(Self, &'a mut AnyTile)> {
+
+        let ptr: *const Pane = &*pane;
+        let tile = pane.get_mut(position)?.get_mut()?;
+
+        let res = Self {
+            position,
+            pane: ptr,
+            phantom: PhantomData
+        };
+
+        Some((res, tile))
+    }
+
+    #[inline]
+    pub fn signal<'b>(&'b self) -> Option<&'b Rc<Signal>> where 'a: 'b {
+        let pane = unsafe { self.pane() };
+
+        // SAFETY: `pane[position].signal` is not borrowed mutably
+        pane.get(self.position).unwrap().signal()
+    }
+
+    /// Returns an immutable reference to the [FullTile] at `pos` in the current [Pane].
+    /// Returns `None` if the tile is the current tile (see [UpdateContext]) or if it does not exist.
+    #[inline]
+    pub fn get<'b>(&'b self, pos: (usize, usize)) -> Option<&'b FullTile> where 'a: 'b {
+        let pane = unsafe { self.pane() };
+
+        // SAFETY: we only access `pane[pos]` if `position != pos`
+        if pos != self.position {
+            pane.get(pos)
+        } else {
+            None
+        }
+    }
+
+    /// Returns `Some((position.x + Δx, position.y + Δy))` iff `(x + Δx, y + Δy)` is inside the pane
+    #[inline]
+    pub fn offset(&self, offset: (i8, i8)) -> Option<(usize, usize)> {
+        let pane = unsafe { self.pane() };
+
+        // SAFETY: pane.offset does not access pane[position].cell
+        pane.offset(self.position, offset)
+    }
+
+    // SAFETY: `self.pane` originates from a `&'a mut Pane`,
+    // guaranteeing that no accesses may be done outside of ours.
+    // No access to `pane[position].cell` may be done!
+    #[inline]
+    unsafe fn pane<'b>(&'b self) -> &'b Pane {
+        &*self.pane
+    }
+}
+
+/// An UpdateContext is created for every tile update during the "transmit" phase,
+/// and it contains the necessary data for a tile to transmit its internal signal to other tiles.
+///
+/// During this phase, the tile may access itself through an immutable borrow and its signal through an owned reference.
+/// It may access the other tiles immutably, but it cannot access the other signals.
+
+// SAFETY: this structures ensures that it has exlusive, mutable access to `∀x, pane[x].signal` and `pane.signals`.
+// Other parts of `pane` may be accessed and returned immutably.
+pub struct TransmitContext<'a> {
+    pub position: (usize, usize),
+    pane: *mut Pane,
+
+    phantom: PhantomData<&'a mut Pane>,
+}
+
+impl<'a> TransmitContext<'a> {
+    pub(crate) fn new(pane: &'a mut Pane, position: (usize, usize)) -> Option<(Self, &'a AnyTile, Rc<Signal>)> {
+        let ptr: *mut Pane = &mut *pane;
+        // SAFETY: no mutable accesses to `∀x, pane[x].cell` are made by `TransmitContext`
+        let tile: &AnyTile = unsafe {
+            (*ptr).get(position).unwrap().get()?
+        };
+        let signal = pane.get_mut(position)?.take_signal()?;
+
+        let res = Self {
+            position,
+            pane: ptr,
+
+            phantom: PhantomData
+        };
+
+        Some((res, tile, signal))
+    }
+
+    /// Returns an immutable reference to the [tile](AnyTile) at `pos` in the current [Pane].
+    /// Returns `None` if that tile does not exist.
+    #[inline]
+    pub fn get<'b>(&'b self, pos: (usize, usize)) -> Option<&'b AnyTile> where 'a: 'b {
+        let pane = unsafe { self.pane() };
+
+        // SAFETY: we only return pane[pos].cell
+        pane.get(pos)?.get()
+    }
+
+    /// Sends a signal to be stored in a cell (may be the current one), the signal overrides that of the other cell
+    /// Returns true if the signal was stored in a cell, false otherwise
+    pub fn send<'b>(&'b self, pos: (usize, usize), signal: Signal) -> bool where 'a: 'b {
+        // SAFETY: we do not return any reference to any data borrowed in this function
+        // SAFETY: we only access `pane[pos].signal` and `pane.signals`
+        let pane = unsafe { self.pane_mut() };
+
+        match pane.get_mut(pos) {
+            Some(ref mut tile) => {
+                if let Some(weak) = tile.set_signal(signal) {
+                    pane.signals.push(weak);
+                    true
+                } else {
+                    false
+                }
+            }
+            _ => false
+        }
+    }
+
+    /// Returns `Some((position.x + Δx, position.y + Δy))` iff `(x + Δx, y + Δy)` is inside the pane
+    #[inline]
+    pub fn offset(&self, offset: (i8, i8)) -> Option<(usize, usize)> {
+        let pane = unsafe { self.pane() };
+
+        // SAFETY: pane.offset does not access pane[position].signal or pane.signals
+        pane.offset(self.position, offset)
+    }
+
+    // SAFETY: `self.pane` originates from a `&'a mut Pane`,
+    // guaranteeing that no accesses may be done outside of ours.
+    #[inline]
+    unsafe fn pane<'b>(&'b self) -> &'b Pane {
+        &*self.pane
+    }
+
+    // SAFETY: `self.pane` originates from a `&'a mut Pane`,
+    // guaranteeing that no accesses may be done outside of ours.
+    #[inline]
+    unsafe fn pane_mut<'b>(&'b self) -> &'b mut Pane {
+        &mut *self.pane
+    }
+}

stackline/src/lib.rs

@@ -1,4 +1,3 @@
-use std::cell::RefCell;
 use std::num::NonZeroUsize;
 use std::rc::Weak;
 
@@ -11,44 +10,36 @@ use tile::*;
 mod signal;
 pub use signal::*;
 
+pub mod context;
+use context::*;
+
 pub struct World {
-    tiles: Vec<RefCell<FullTile>>,
+    panes: Vec<Pane>,
+}
+
+pub struct Pane {
+    tiles: Vec<FullTile>,
     width: NonZeroUsize,
     height: NonZeroUsize,
 
     signals: Vec<Weak<Signal>>,
 }
 
-impl World {
+impl Pane {
     pub fn empty(width: usize, height: usize) -> Option<Self> {
         // TODO: check that width * height is a valid usize
 
         Some(Self {
             width: width.try_into().ok()?,
             height: height.try_into().ok()?,
-            tiles: vec![RefCell::new(FullTile::default()); width * height],
+            tiles: vec![FullTile::default(); width * height],
 
             signals: vec![],
         })
     }
 
-    pub fn send_signal(
-        &mut self,
-        position: (usize, usize),
-        signal: Signal,
-    ) -> Option<Weak<Signal>> {
-        let tile = self.get(position)?;
-        let weak = {
-            let mut guard = tile.try_borrow_mut().ok()?;
-            guard.set_signal(signal)?
-        };
-
-        self.signals.push(weak.clone());
-
-        Some(weak)
-    }
-
     /// Returns `Some((x + Δx, y + Δy))` iff `(x + Δx, y + Δy)` is inside the world
+    // SAFETY: this function may *not* access `self.signals`, `∀x, self.tiles[x].cell` or `∀x, self.tiles[x].signal`
     #[inline]
     pub fn offset(&self, position: (usize, usize), offset: (i8, i8)) -> Option<(usize, usize)> {
         if offset.0 < 0 && (-offset.0) as usize > position.0
@@ -71,7 +62,7 @@ impl World {
     }
 
     #[inline]
-    pub fn get<'b>(&'b self, position: (usize, usize)) -> Option<&'b RefCell<FullTile>> {
+    pub fn get<'b>(&'b self, position: (usize, usize)) -> Option<&'b FullTile> {
         if !self.in_bounds(position) {
             return None;
         }
@@ -79,6 +70,15 @@ impl World {
         self.tiles.get(position.1 * self.width.get() + position.0)
     }
 
+    #[inline]
+    pub fn get_mut<'b>(&'b mut self, position: (usize, usize)) -> Option<&'b mut FullTile> {
+        if !self.in_bounds(position) {
+            return None;
+        }
+
+        self.tiles.get_mut(position.1 * self.width.get() + position.0)
+    }
+
     #[inline]
     pub fn in_bounds(&self, position: (usize, usize)) -> bool {
         position.0 < self.width.get() && position.1 < self.height.get()

stackline/src/tile/mod.rs

@@ -18,22 +18,15 @@ Cloning a `FullTile` results in a `FullTile` that does not have any signal.
 pub struct FullTile {
     cell: Option<AnyTile>,
     signal: Option<Rc<Signal>>,
+    // TODO: state
 }
 
+// SAFETY: should not implement Tile
 impl FullTile {
     pub fn new(cell: Option<AnyTile>) -> Self {
         Self { cell, signal: None }
     }
 
-    pub fn update(&mut self, world: &mut World, pos: (usize, usize)) {
-        match self.cell {
-            Some(ref mut tile) => {
-                tile.update(world, &mut self.signal, pos);
-            }
-            None => {}
-        }
-    }
-
     pub fn accepts_signal(&self, direction: Direction) -> bool {
         match self.cell {
             Some(ref tile) => tile.accepts_signal(direction),
@@ -42,7 +35,7 @@ impl FullTile {
     }
 
     /// Returns Some(signal) iff self.cell.is_some()
-    pub fn set_signal(&mut self, signal: Signal) -> Option<Weak<Signal>> {
+    pub(crate) fn set_signal(&mut self, signal: Signal) -> Option<Weak<Signal>> {
         if self.cell.is_some() {
             let rc = Rc::new(signal);
             let weak = Rc::downgrade(&rc);
@@ -52,6 +45,24 @@ impl FullTile {
             None
         }
     }
+
+    /// Returns the internal state of this full tile
+    pub fn get<'b>(&'b self) -> Option<&'b AnyTile> {
+        self.cell.as_ref()
+    }
+
+    /// Returns the signal of this tile
+    pub fn signal<'b>(&'b self) -> Option<&'b Rc<Signal>> {
+        self.signal.as_ref()
+    }
+
+    pub(crate) fn take_signal(&mut self) -> Option<Rc<Signal>> {
+        std::mem::take(&mut self.signal)
+    }
+
+    pub(crate) fn get_mut<'b>(&'b mut self) -> Option<&'b mut AnyTile> {
+        self.cell.as_mut()
+    }
 }
 
 impl Default for FullTile {
@@ -61,7 +72,12 @@ impl Default for FullTile {
 }
 
 pub trait Tile: DynClone + std::fmt::Debug {
-    fn update(&mut self, world: &mut World, signal: &mut Option<Rc<Signal>>, pos: (usize, usize));
+    /// Function to be called when the tile needs to update its internal state.
+    /// During the "update" phase, the tile may access its signal and the other tiles immutably.
+    fn update<'b>(&'b mut self, _context: UpdateContext<'b>) {}
+
+    /// Function that will be called if the tile has a signal.
+    fn transmit<'b>(&'b self, signal: Rc<Signal>, context: TransmitContext<'b>);
 
     /// Should return true iff the tile accepts a signal travelling in `Direction`
     fn accepts_signal(&self, _direction: Direction) -> bool {
@@ -73,8 +89,8 @@ pub trait Tile: DynClone + std::fmt::Debug {
 pub struct AnyTile(Box<dyn Tile>);
 
 impl AnyTile {
-    fn update(&mut self, world: &mut World, signal: &mut Option<Rc<Signal>>, pos: (usize, usize)) {
-        self.0.update(world, signal, pos)
+    fn update<'b>(&'b mut self, ctx: UpdateContext<'b>) {
+        self.0.update(ctx)
     }
 
     fn accepts_signal(&self, direction: Direction) -> bool {

stackline/src/tile/wire.rs

@@ -6,18 +6,16 @@ use super::*;
 pub struct Wire(Orientation);
 
 impl Tile for Wire {
-    fn update(&mut self, world: &mut World, signal: &mut Option<Rc<Signal>>, pos: (usize, usize)) {
-        if let Some(signal) = std::mem::take(signal) {
-            for &direction in self.0.into_directions() {
-                if direction == signal.direction.opposite() {
-                    continue;
-                }
+    fn transmit<'b>(&'b self, signal: Rc<Signal>, context: TransmitContext<'b>) {
+        for &direction in self.0.into_directions() {
+            if direction == signal.direction.opposite() {
+                continue;
+            }
 
-                if let Some(new_pos) = world.offset(pos, direction.into_offset()) {
-                    let tile = world.get(new_pos).unwrap();
-                    if tile.borrow().accepts_signal(direction) {
-                        world.send_signal(new_pos, (*signal).clone_with_dir(direction)).unwrap();
-                    }
+            if let Some(new_pos) = context.offset(direction.into_offset()) {
+                let tile = context.get(new_pos);
+                if tile.map(|t| t.accepts_signal(direction)).unwrap_or(false) {
+                    context.send(new_pos, (*signal).clone_with_dir(direction));
                 }
             }
         }
@@ -31,15 +29,15 @@ impl Tile for Wire {
 #[derive(Clone, Debug)]
 pub struct Diode(Direction);
 
-impl Tile for Diode {
-    fn update(&mut self, world: &mut World, signal: &mut Option<Rc<Signal>>, pos: (usize, usize)) {
-        if let Some(signal) = std::mem::take(signal) {
-            if let Some(new_pos) = world.offset(pos, self.0.into_offset()) {
-                let tile = world.get(new_pos).unwrap();
-                if tile.borrow().accepts_signal(self.0) {
-                    world.send_signal(new_pos, (*signal).clone_with_dir(self.0)).unwrap();
-                }
-            }
-        }
-    }
-}
+// impl Tile for Diode {
+//     fn update(&mut self, world: &mut World, signal: &mut Option<Rc<Signal>>, pos: (usize, usize)) {
+//         if let Some(signal) = std::mem::take(signal) {
+//             if let Some(new_pos) = world.offset(pos, self.0.into_offset()) {
+//                 let tile = world.get(new_pos).unwrap();
+//                 if tile.borrow().accepts_signal(self.0) {
+//                     world.send_signal(new_pos, (*signal).clone_with_dir(self.0)).unwrap();
+//                 }
+//             }
+//         }
+//     }
+// }