rust: types: introduce ForeignOwnable

It was originally called `PointerWrapper`. It is used to convert
a Rust object to a pointer representation (void *) that can be
stored on the C side, used, and eventually returned to Rust.

Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Wedson Almeida Filho 2023-01-30 03:44:01 -03:00 committed by Miguel Ojeda
parent 4d4692a2ff
commit 0fc4424d24
2 changed files with 55 additions and 0 deletions

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@ -16,6 +16,7 @@
#![feature(coerce_unsized)]
#![feature(core_ffi_c)]
#![feature(dispatch_from_dyn)]
#![feature(generic_associated_types)]
#![feature(receiver_trait)]
#![feature(unsize)]

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@ -8,6 +8,60 @@ use core::{
ops::{Deref, DerefMut},
};
/// Used to transfer ownership to and from foreign (non-Rust) languages.
///
/// Ownership is transferred from Rust to a foreign language by calling [`Self::into_foreign`] and
/// later may be transferred back to Rust by calling [`Self::from_foreign`].
///
/// This trait is meant to be used in cases when Rust objects are stored in C objects and
/// eventually "freed" back to Rust.
pub trait ForeignOwnable: Sized {
/// Type of values borrowed between calls to [`ForeignOwnable::into_foreign`] and
/// [`ForeignOwnable::from_foreign`].
type Borrowed<'a>;
/// Converts a Rust-owned object to a foreign-owned one.
///
/// The foreign representation is a pointer to void.
fn into_foreign(self) -> *const core::ffi::c_void;
/// Borrows a foreign-owned object.
///
/// # Safety
///
/// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
/// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
/// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow_mut`]
/// for this object must have been dropped.
unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Self::Borrowed<'a>;
/// Mutably borrows a foreign-owned object.
///
/// # Safety
///
/// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
/// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
/// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and
/// [`ForeignOwnable::borrow_mut`] for this object must have been dropped.
unsafe fn borrow_mut(ptr: *const core::ffi::c_void) -> ScopeGuard<Self, fn(Self)> {
// SAFETY: The safety requirements ensure that `ptr` came from a previous call to
// `into_foreign`.
ScopeGuard::new_with_data(unsafe { Self::from_foreign(ptr) }, |d| {
d.into_foreign();
})
}
/// Converts a foreign-owned object back to a Rust-owned one.
///
/// # Safety
///
/// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
/// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
/// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and
/// [`ForeignOwnable::borrow_mut`] for this object must have been dropped.
unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self;
}
/// Runs a cleanup function/closure when dropped.
///
/// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.