Struct ArcBorrow

pub struct ArcBorrow<'a, T: ?Sized + 'a> { /* private fields */ }

A borrowed reference to an Arc instance.

For cases when one doesn’t ever need to increment the refcount on the allocation, it is simpler to use just &T, which we can trivially get from an Arc<T> instance.

However, when one may need to increment the refcount, it is preferable to use an ArcBorrow<T> over &Arc<T> because the latter results in a double-indirection: a pointer (shared reference) to a pointer (Arc<T>) to the object (T). An ArcBorrow eliminates this double indirection while still allowing one to increment the refcount and getting an Arc<T> when/if needed.

Invariants

There are no mutable references to the underlying Arc, and it remains valid for the lifetime of the ArcBorrow instance.

Examples

use kernel::sync::{Arc, ArcBorrow};

struct Example;

fn do_something(e: ArcBorrow<'_, Example>) -> Arc<Example> {
    e.into()
}

let obj = Arc::new(Example, GFP_KERNEL)?;
let cloned = do_something(obj.as_arc_borrow());

// Assert that both `obj` and `cloned` point to the same underlying object.
assert!(core::ptr::eq(&*obj, &*cloned));

Using ArcBorrow<T> as the type of self:

use kernel::sync::{Arc, ArcBorrow};

struct Example {
    a: u32,
    b: u32,
}

impl Example {
    fn use_reference(self: ArcBorrow<'_, Self>) {
        // ...
    }
}

let obj = Arc::new(Example { a: 10, b: 20 }, GFP_KERNEL)?;
obj.as_arc_borrow().use_reference();

Implementations

impl<T: ?Sized> ArcBorrow<'_, T>

pub unsafe fn from_raw(ptr: *const T) -> Self

Creates an ArcBorrow to an Arc that has previously been deconstructed with Arc::into_raw or Arc::as_ptr.

Safety

• The provided pointer must originate from a call to Arc::into_raw or Arc::as_ptr.
• For the duration of the lifetime annotated on this ArcBorrow, the reference count must not hit zero.
• For the duration of the lifetime annotated on this ArcBorrow, there must not be a UniqueArc reference to this value.

Trait Implementations

impl<T: ?Sized> Clone for ArcBorrow<'_, T>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: ?Sized> Deref for ArcBorrow<'_, T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<T: ?Sized> From<ArcBorrow<'_, T>> for Arc<T>

fn from(b: ArcBorrow<'_, T>) -> Self

Converts to this type from the input type.

impl<'a, T: ?Sized + 'a + Unsize<__S>, __S: ?Sized + 'a> CoerceUnsized<ArcBorrow<'a, __S>> for ArcBorrow<'a, T>

impl<T: ?Sized> Copy for ArcBorrow<'_, T>

impl<'a, T: ?Sized + 'a + Unsize<__S>, __S: ?Sized + 'a> DispatchFromDyn<ArcBorrow<'a, __S>> for ArcBorrow<'a, T>