experimental/scene: remove bumpalo dependency

Author: not-fl3

Cargo.toml

@@ -33,7 +33,6 @@ glam = {version = "0.27", features = ["scalar-math"] }
 image = { version = "0.24", default-features = false, features = ["png", "tga"] }
 macroquad_macro = { version = "0.1.8", path = "macroquad_macro" }
 fontdue = "0.7"
-bumpalo = "3.4"
 backtrace = { version = "0.3.60", optional = true, default-features = false, features = [ "std", "libbacktrace" ] }
 log = { version = "0.4", optional = true }
 quad-snd = { version = "0.2", optional = true }

src/experimental/scene.rs

@@ -4,6 +4,8 @@ use crate::camera::Camera2D;
 
 pub use macroquad_macro::CapabilityTrait;
 
+mod arena;
+
 #[rustfmt::skip]
 pub trait Node {
     fn ready(_node: RefMut<Self>) where Self: Sized {}
@@ -12,10 +14,6 @@ pub trait Node {
     fn draw(_node: RefMut<Self>) where Self: Sized  {}
 }
 
-trait NodeTyped<T> {
-    fn self_node(&self) -> &T;
-}
-
 trait NodeAny: Any + Node {
     fn as_any(&self) -> &dyn Any;
     fn as_any_mut(&mut self) -> &mut dyn Any;
@@ -345,7 +343,7 @@ struct Scene {
     dense: Vec<Id>,
     dense_ongoing: Vec<Result<Id, Id>>,
     nodes: Vec<Option<Cell>>,
-    arena: bumpalo::Bump,
+    arena: arena::Arena,
     camera: [Option<Camera2D>; 4],
     camera_pos: crate::Vec2,
 
@@ -363,7 +361,7 @@ impl Scene {
             dense: vec![],
             dense_ongoing: vec![],
             nodes: Vec::new(),
-            arena: bumpalo::Bump::new(),
+            arena: arena::Arena::new(),
             free_nodes: Vec::new(),
             camera: [Some(Camera2D::default()), None, None, None],
             camera_pos: crate::vec2(0., 0.),
@@ -461,15 +459,22 @@ impl Scene {
             let trait_obj = &data as &dyn NodeAny;
             let (_, vtable) = unsafe { std::mem::transmute::<_, (*mut (), *mut ())>(trait_obj) };
 
-            let data = self.arena.alloc(data) as *mut _ as *mut _;
-            let used = self.arena.alloc(false) as *mut _ as *mut _;
+            let ptr = self.arena.alloc(std::mem::size_of::<T>()) as *mut _ as *mut T;
+            unsafe {
+                std::ptr::write(ptr, data);
+            }
+            let ptr = ptr as *mut ();
+            let used = self.arena.alloc(1) as *mut _ as *mut bool;
+            unsafe {
+                std::ptr::write(used, false);
+            }
+            let used = used as *mut _ as *mut bool;
 
             id = Id {
                 id: self.nodes.len(),
                 generation: 0,
             };
-            self.nodes
-                .push(Some(Cell::new::<T>(id, data, vtable, used)));
+            self.nodes.push(Some(Cell::new::<T>(id, ptr, vtable, used)));
         }
 
         self.dense.push(id);
@@ -616,7 +621,7 @@ unsafe fn get_scene() -> &'static mut Scene {
 }
 
 pub(crate) fn allocated_memory() -> usize {
-    unsafe { get_scene() }.arena.allocated_bytes()
+    unsafe { get_scene().arena.offset() }
 }
 
 pub fn clear() {

src/experimental/scene/arena.rs

@@ -0,0 +1,91 @@
+//! Gleaned from https://github.com/ratel-rust/toolshed/blob/master/src/arena.rs
+//! and than modified a lot.
+//!
+//! Module containing the `Arena` and `Uninitialized` structs. For convenience the
+//! `Arena` is exported at the root of the crate.
+
+use std::cell::Cell;
+use std::mem::size_of;
+
+const ARENA_BLOCK: usize = 64 * 1024;
+
+/// An arena implementation that uses preallocated 64KiB pages for all allocations.
+/// If a new allocation were to be pushed over the the boundaries of the page, a
+/// new page is internally allocated first, thus this version of the arena can never
+/// run out of memory unless the process runs out of heap altogether.
+///
+/// Allocating a type larger than the page size will result in a new heap allocation
+/// just for that type separate from the page mechanism.
+pub struct Arena {
+    store: Cell<Vec<Vec<u8>>>,
+    ptr: Cell<*mut u8>,
+    offset: Cell<usize>,
+}
+
+impl Arena {
+    /// Create a new arena with a single preallocated 64KiB page.
+    pub fn new() -> Self {
+        let mut store = vec![Vec::with_capacity(ARENA_BLOCK)];
+        let ptr = store[0].as_mut_ptr();
+
+        Arena {
+            store: Cell::new(store),
+            ptr: Cell::new(ptr),
+            offset: Cell::new(0),
+        }
+    }
+
+    pub fn alloc(&self, size: usize) -> *mut u8 {
+        // This should be optimized away for size known at compile time.
+        if size > ARENA_BLOCK {
+            return self.alloc_bytes(size);
+        }
+
+        let size = match size % size_of::<usize>() {
+            0 => size,
+            n => size + (size_of::<usize>() - n),
+        };
+
+        let offset = self.offset.get();
+        let cap = offset + size;
+
+        if cap > ARENA_BLOCK {
+            self.grow();
+
+            self.offset.set(size);
+            self.ptr.get()
+        } else {
+            self.offset.set(cap);
+            unsafe { self.ptr.get().add(offset) }
+        }
+    }
+
+    #[inline]
+    fn alloc_byte_vec(&self, mut val: Vec<u8>) -> *mut u8 {
+        let ptr = val.as_mut_ptr();
+
+        let mut temp = self.store.replace(Vec::new());
+        temp.push(val);
+        self.store.replace(temp);
+
+        ptr
+    }
+
+    pub fn grow(&self) {
+        let ptr = self.alloc_byte_vec(Vec::with_capacity(ARENA_BLOCK));
+        self.ptr.set(ptr);
+    }
+
+    fn alloc_bytes(&self, size: usize) -> *mut u8 {
+        self.alloc_byte_vec(Vec::with_capacity(size))
+    }
+
+    #[doc(hidden)]
+    #[inline]
+    pub unsafe fn offset(&self) -> usize {
+        self.offset.get()
+    }
+}
+
+/// Akin to `CopyCell`: `Sync` is unsafe but `Send` is totally fine!
+unsafe impl Send for Arena {}