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[Merged by Bors] - Allow shared access to SyncCell for types that are already Sync #7718

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[Merged by Bors] - Allow shared access to SyncCell for types that are already Sync #7718

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f63f490
add `SyncCell::read`
JoJoJet Feb 16, 2023
8a757ae
use imperative tense
JoJoJet Feb 16, 2023
f9d183e
tweak safety comment
JoJoJet Feb 16, 2023
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12 changes: 10 additions & 2 deletions crates/bevy_utils/src/synccell.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,14 @@ impl<T: ?Sized> SyncCell<T> {
&mut self.inner
}

/// For types that implement [`Sync`], get shared access to this `SyncCell`'s inner value.
pub fn read(&self) -> &T
where
T: Sync,
{
&self.inner
}

/// Build a mutable reference to a `SyncCell` from a mutable reference
/// to its inner value, to skip constructing with [`new()`](SyncCell::new()).
pub fn from_mut(r: &'_ mut T) -> &'_ mut SyncCell<T> {
Expand All @@ -38,6 +46,6 @@ impl<T: ?Sized> SyncCell<T> {
}

// SAFETY: `Sync` only allows multithreaded access via immutable reference.
// As `SyncCell` requires an exclusive reference to access the wrapped value,
// marking this type as `Sync` does not actually allow threaded access to the inner value.
// As `SyncCell` requires an exclusive reference to access the wrapped value for `!Sync` types,
// marking this type as `Sync` does not actually allow unsychronized access to the inner value.
unsafe impl<T: ?Sized> Sync for SyncCell<T> {}