97 lines
3.4 KiB
Rust
97 lines
3.4 KiB
Rust
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// SPDX-License-Identifier: GPL-2.0
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// Copyright (C) 2024 Google LLC.
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//! A field that is exclusively owned by a [`ListArc`].
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//!
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//! This can be used to have reference counted struct where one of the reference counted pointers
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//! has exclusive access to a field of the struct.
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//!
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//! [`ListArc`]: crate::list::ListArc
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use core::cell::UnsafeCell;
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/// A field owned by a specific [`ListArc`].
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///
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/// [`ListArc`]: crate::list::ListArc
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pub struct ListArcField<T, const ID: u64 = 0> {
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value: UnsafeCell<T>,
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}
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// SAFETY: If the inner type is thread-safe, then it's also okay for `ListArc` to be thread-safe.
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unsafe impl<T: Send + Sync, const ID: u64> Send for ListArcField<T, ID> {}
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// SAFETY: If the inner type is thread-safe, then it's also okay for `ListArc` to be thread-safe.
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unsafe impl<T: Send + Sync, const ID: u64> Sync for ListArcField<T, ID> {}
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impl<T, const ID: u64> ListArcField<T, ID> {
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/// Creates a new `ListArcField`.
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pub fn new(value: T) -> Self {
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Self {
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value: UnsafeCell::new(value),
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}
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}
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/// Access the value when we have exclusive access to the `ListArcField`.
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///
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/// This allows access to the field using an `UniqueArc` instead of a `ListArc`.
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pub fn get_mut(&mut self) -> &mut T {
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self.value.get_mut()
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}
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/// Unsafely assert that you have shared access to the `ListArc` for this field.
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///
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/// # Safety
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///
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/// The caller must have shared access to the `ListArc<ID>` containing the struct with this
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/// field for the duration of the returned reference.
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pub unsafe fn assert_ref(&self) -> &T {
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// SAFETY: The caller has shared access to the `ListArc`, so they also have shared access
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// to this field.
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unsafe { &*self.value.get() }
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}
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/// Unsafely assert that you have mutable access to the `ListArc` for this field.
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///
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/// # Safety
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///
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/// The caller must have mutable access to the `ListArc<ID>` containing the struct with this
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/// field for the duration of the returned reference.
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#[expect(clippy::mut_from_ref)]
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pub unsafe fn assert_mut(&self) -> &mut T {
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// SAFETY: The caller has exclusive access to the `ListArc`, so they also have exclusive
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// access to this field.
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unsafe { &mut *self.value.get() }
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}
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}
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/// Defines getters for a [`ListArcField`].
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#[macro_export]
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macro_rules! define_list_arc_field_getter {
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($pub:vis fn $name:ident(&self $(<$id:tt>)?) -> &$typ:ty { $field:ident }
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$($rest:tt)*
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) => {
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$pub fn $name<'a>(self: &'a $crate::list::ListArc<Self $(, $id)?>) -> &'a $typ {
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let field = &(&**self).$field;
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// SAFETY: We have a shared reference to the `ListArc`.
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unsafe { $crate::list::ListArcField::<$typ $(, $id)?>::assert_ref(field) }
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}
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$crate::list::define_list_arc_field_getter!($($rest)*);
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};
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($pub:vis fn $name:ident(&mut self $(<$id:tt>)?) -> &mut $typ:ty { $field:ident }
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$($rest:tt)*
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) => {
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$pub fn $name<'a>(self: &'a mut $crate::list::ListArc<Self $(, $id)?>) -> &'a mut $typ {
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let field = &(&**self).$field;
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// SAFETY: We have a mutable reference to the `ListArc`.
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unsafe { $crate::list::ListArcField::<$typ $(, $id)?>::assert_mut(field) }
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}
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$crate::list::define_list_arc_field_getter!($($rest)*);
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};
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() => {};
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}
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pub use define_list_arc_field_getter;
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