Replace TrustCell implementation with atomic_refcell::AtomicRefCell

Cargo.toml

@@ -19,6 +19,7 @@ rust-version = "1.59.0"
 [dependencies]
 ahash = "0.7.6"
 arrayvec = "0.7.2"
+atomic_refcell = "0.1.10" # part of public API
 rayon = { version = "1.5.0", optional = true }
 shred-derive = { path = "shred-derive", version = "0.6.3", optional = true }
 smallvec = "1.6.1"

benches/bench.rs

@@ -241,11 +241,14 @@ fn bench_fetching(b: &mut Bencher) {
 
 #[bench]
 fn bench_indirection_refs(b: &mut Bencher) {
-    use shred::cell::{Ref, TrustCell};
+    use shred::cell::{AtomicRef, AtomicRefCell};
     use std::ops::Deref;
 
-    let cell = TrustCell::new(Box::new(10));
-    let refs: Vec<Ref<'_, Box<usize>>> = std::iter::repeat(cell.borrow()).take(10000).collect();
+    let cell = AtomicRefCell::new(Box::new(10));
+    let borrow = cell.borrow();
+    let refs: Vec<AtomicRef<'_, Box<usize>>> = std::iter::repeat_with(|| AtomicRef::clone(&borrow))
+        .take(10000)
+        .collect();
 
     b.iter(|| {
         let sum: usize = refs.iter().map(|v| v.deref().deref()).sum();
@@ -255,13 +258,15 @@ fn bench_indirection_refs(b: &mut Bencher) {
 
 #[bench]
 fn bench_direct_refs(b: &mut Bencher) {
-    use shred::cell::{Ref, TrustCell};
+    use shred::cell::{AtomicRef, AtomicRefCell};
     use std::ops::Deref;
 
-    let cell = TrustCell::new(Box::new(10));
-    let refs: Vec<Ref<'_, usize>> = std::iter::repeat(cell.borrow().map(Box::as_ref))
-        .take(10000)
-        .collect();
+    let cell = AtomicRefCell::new(Box::new(10));
+    let mapped_borrow = AtomicRef::map(cell.borrow(), Box::as_ref);
+    let refs: Vec<AtomicRef<'_, usize>> =
+        std::iter::repeat_with(|| AtomicRef::clone(&mapped_borrow))
+            .take(10000)
+            .collect();
 
     b.iter(|| {
         let sum: usize = refs.iter().map(|v| v.deref()).sum();

examples/dyn_sys_data.rs

@@ -11,7 +11,7 @@ extern crate shred;
 use ahash::AHashMap as HashMap;
 
 use shred::{
-    cell::{Ref, RefMut},
+    cell::{AtomicRef, AtomicRefMut},
     Accessor, AccessorCow, CastFrom, DispatcherBuilder, DynamicSystemData, MetaTable, Read,
     Resource, ResourceId, System, SystemData, World,
 };
@@ -54,32 +54,20 @@ impl<'a> System<'a> for DynamicSystem {
         let reads: Vec<&dyn Reflection> = data
             .reads
             .iter()
-            .map(|resource| {
-                // explicitly use the type because we're dealing with `&Resource` which is
-                // implemented by a lot of types; we don't want to accidentally
-                // get a `&Box<Resource>` and cast it to a `&Resource`.
-                let res = Box::as_ref(resource);
-
-                meta.get(res).expect("Not registered in meta table")
-            })
+            .map(|resource| meta.get(&**resource).expect("Not registered in meta table"))
             .collect();
 
         let writes: Vec<&mut dyn Reflection> = data
             .writes
             .iter_mut()
             .map(|resource| {
-                // explicitly use the type because we're dealing with `&mut Resource` which is
-                // implemented by a lot of types; we don't want to accidentally get a
-                // `&mut Box<Resource>` and cast it to a `&mut Resource`.
-                let res = Box::as_mut(resource);
-
                 // For some reason this needs a type ascription, otherwise Rust will think it's
-                // a `&mut (Reflection + '_)` (as opposed to `&mut (Reflection + 'static)`.
-                let res: &mut dyn Reflection = meta.get_mut(res).expect(
+                // a `&mut (Reflaction + '_)` (as opposed to `&mut (Reflection + 'static)`. (Note this
+                // isn't needed in newer rust version but fails on the MSRV of 1.59.0).
+                let res: &mut dyn Reflection = meta.get_mut(&mut **resource).expect(
                     "Not registered in meta \
                      table",
                 );
-
                 res
             })
             .collect();
@@ -150,37 +138,47 @@ struct ScriptInput<'a> {
 
 struct ScriptSystemData<'a> {
     meta_table: Read<'a, ReflectionTable>,
-    reads: Vec<Ref<'a, Box<dyn Resource + 'static>>>,
-    writes: Vec<RefMut<'a, Box<dyn Resource + 'static>>>,
+    reads: Vec<AtomicRef<'a, dyn Resource + 'static>>,
+    writes: Vec<AtomicRefMut<'a, dyn Resource + 'static>>,
 }
 
 impl<'a> DynamicSystemData<'a> for ScriptSystemData<'a> {
     type Accessor = Dependencies;
 
     fn setup(_accessor: &Dependencies, _res: &mut World) {}
 
-    fn fetch(access: &Dependencies, res: &'a World) -> Self {
+    fn fetch(access: &Dependencies, world: &'a World) -> Self {
         let reads = access
             .reads
             .iter()
             .map(|id| {
-                res.try_fetch_internal(id.clone())
-                    .expect("bug: the requested resource does not exist")
-                    .borrow()
+                let id = id.clone();
+                // SAFETY: We don't expose mutable reference to the Box or swap it out.
+                let res = unsafe { world.try_fetch_internal(id) };
+                AtomicRef::map(
+                    res.expect("bug: the requested resource does not exist")
+                        .borrow(),
+                    Box::as_ref,
+                )
             })
             .collect();
         let writes = access
             .writes
             .iter()
             .map(|id| {
-                res.try_fetch_internal(id.clone())
-                    .expect("bug: the requested resource does not exist")
-                    .borrow_mut()
+                let id = id.clone();
+                // SAFETY: We don't expose mutable reference to the Box or swap it out.
+                let res = unsafe { world.try_fetch_internal(id) };
+                AtomicRefMut::map(
+                    res.expect("bug: the requested resource does not exist")
+                        .borrow_mut(),
+                    Box::as_mut,
+                )
             })
             .collect();
 
         ScriptSystemData {
-            meta_table: SystemData::fetch(res),
+            meta_table: SystemData::fetch(world),
             reads,
             writes,
         }