mirror of
https://github.com/servo/servo.git
synced 2025-07-10 00:43:39 +01:00
66 lines
2 KiB
Rust
66 lines
2 KiB
Rust
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
|
|
|
|
//! A thin atomically-reference-counted slice.
|
|
|
|
use servo_arc::ThinArc;
|
|
use std::mem;
|
|
use std::ops::Deref;
|
|
use std::ptr::NonNull;
|
|
|
|
/// A canary that we stash in ArcSlices.
|
|
///
|
|
/// Given we cannot use a zero-sized-type for the header, since well, C++
|
|
/// doesn't have zsts, and we want to use cbindgen for this type, we may as well
|
|
/// assert some sanity at runtime.
|
|
const ARC_SLICE_CANARY: u32 = 0xf3f3f3f3;
|
|
|
|
/// A wrapper type for a refcounted slice using ThinArc.
|
|
///
|
|
/// cbindgen:derive-eq=false
|
|
/// cbindgen:derive-neq=false
|
|
#[repr(C)]
|
|
#[derive(Clone, Debug, Eq, PartialEq, ToShmem)]
|
|
pub struct ArcSlice<T>(#[shmem(field_bound)] ThinArc<u32, T>);
|
|
|
|
impl<T> Deref for ArcSlice<T> {
|
|
type Target = [T];
|
|
|
|
#[inline]
|
|
fn deref(&self) -> &Self::Target {
|
|
debug_assert_eq!(self.0.header.header, ARC_SLICE_CANARY);
|
|
&self.0.slice
|
|
}
|
|
}
|
|
|
|
/// The inner pointer of an ArcSlice<T>, to be sent via FFI.
|
|
/// The type of the pointer is a bit of a lie, we just want to preserve the type
|
|
/// but these pointers cannot be constructed outside of this crate, so we're
|
|
/// good.
|
|
#[repr(C)]
|
|
pub struct ForgottenArcSlicePtr<T>(NonNull<T>);
|
|
|
|
impl<T> ArcSlice<T> {
|
|
/// Creates an Arc for a slice using the given iterator to generate the
|
|
/// slice.
|
|
#[inline]
|
|
pub fn from_iter<I>(items: I) -> Self
|
|
where
|
|
I: Iterator<Item = T> + ExactSizeIterator,
|
|
{
|
|
ArcSlice(ThinArc::from_header_and_iter(ARC_SLICE_CANARY, items))
|
|
}
|
|
|
|
/// Creates a value that can be passed via FFI, and forgets this value
|
|
/// altogether.
|
|
#[inline]
|
|
#[allow(unsafe_code)]
|
|
pub fn forget(self) -> ForgottenArcSlicePtr<T> {
|
|
let ret = unsafe {
|
|
ForgottenArcSlicePtr(NonNull::new_unchecked(self.0.ptr() as *const _ as *mut _))
|
|
};
|
|
mem::forget(self);
|
|
ret
|
|
}
|
|
}
|