bevy_utils/
synccell.rs

1#![expect(unsafe_code, reason = "SyncCell requires unsafe code.")]
2
3//! A reimplementation of the currently unstable [`std::sync::Exclusive`]
4//!
5//! [`std::sync::Exclusive`]: https://doc.rust-lang.org/nightly/std/sync/struct.Exclusive.html
6
7use core::ptr;
8
9/// See [`Exclusive`](https://github.com/rust-lang/rust/issues/98407) for stdlib's upcoming implementation,
10/// which should replace this one entirely.
11///
12/// Provides a wrapper that allows making any type unconditionally [`Sync`] by only providing mutable access.
13#[repr(transparent)]
14pub struct SyncCell<T: ?Sized> {
15    inner: T,
16}
17
18impl<T: Sized> SyncCell<T> {
19    /// Construct a new instance of a `SyncCell` from the given value.
20    pub fn new(inner: T) -> Self {
21        Self { inner }
22    }
23
24    /// Deconstruct this `SyncCell` into its inner value.
25    pub fn to_inner(Self { inner }: Self) -> T {
26        inner
27    }
28}
29
30impl<T: ?Sized> SyncCell<T> {
31    /// Get a reference to this `SyncCell`'s inner value.
32    pub fn get(&mut self) -> &mut T {
33        &mut self.inner
34    }
35
36    /// For types that implement [`Sync`], get shared access to this `SyncCell`'s inner value.
37    pub fn read(&self) -> &T
38    where
39        T: Sync,
40    {
41        &self.inner
42    }
43
44    /// Build a mutable reference to a `SyncCell` from a mutable reference
45    /// to its inner value, to skip constructing with [`new()`](SyncCell::new()).
46    pub fn from_mut(r: &'_ mut T) -> &'_ mut SyncCell<T> {
47        // SAFETY: repr is transparent, so refs have the same layout; and `SyncCell` properties are `&mut`-agnostic
48        unsafe { &mut *(ptr::from_mut(r) as *mut SyncCell<T>) }
49    }
50}
51
52// SAFETY: `Sync` only allows multithreaded access via immutable reference.
53// As `SyncCell` requires an exclusive reference to access the wrapped value for `!Sync` types,
54// marking this type as `Sync` does not actually allow unsynchronized access to the inner value.
55unsafe impl<T: ?Sized> Sync for SyncCell<T> {}
bevy_utils/synccell.rs

bevy_utils/
synccell.rs
