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style: Add an owned slice type which cbindgen can understand.
Passing these by value won't be ok of course, but that's fine. I plan to combine this with mozilla/cbindgen#333 to actually be able to share representation for ~all the things, this is just the first bit. Box<T>, Atom and Arc<T> will be much easier since cbindgen can understand them without issues. It's boxed slices the only ones I should need something like this. I could avoid it if I rely on Rust's internal representation, which we can per [1], but then I need to teach cbindgen all about slices, which is generally hard, I think. [1]: https://github.com/rust-lang/unsafe-code-guidelines/blob/master/reference/src/layout/pointers.md Differential Revision: https://phabricator.services.mozilla.com/D29768
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/* 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/. */ | ||
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//! A replacement for `Box<[T]>` that cbindgen can understand. | ||
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use std::marker::PhantomData; | ||
use std::{fmt, mem, slice}; | ||
use std::ptr::NonNull; | ||
use std::ops::{Deref, DerefMut}; | ||
use malloc_size_of::{MallocSizeOf, MallocShallowSizeOf, MallocSizeOfOps}; | ||
use to_shmem::{SharedMemoryBuilder, ToShmem}; | ||
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/// A struct that basically replaces a `Box<[T]>`, but which cbindgen can | ||
/// understand. | ||
/// | ||
/// We could rely on the struct layout of `Box<[T]>` per: | ||
/// | ||
/// https://github.com/rust-lang/unsafe-code-guidelines/blob/master/reference/src/layout/pointers.md | ||
/// | ||
/// But handling fat pointers with cbindgen both in structs and argument | ||
/// positions more generally is a bit tricky. | ||
#[repr(C)] | ||
pub struct OwnedSlice<T: Sized> { | ||
ptr: NonNull<T>, | ||
len: usize, | ||
_phantom: PhantomData<T>, | ||
} | ||
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impl<T: Sized> Default for OwnedSlice<T> { | ||
#[inline] | ||
fn default() -> Self { | ||
Self { | ||
len: 0, | ||
ptr: NonNull::dangling(), | ||
_phantom: PhantomData, | ||
} | ||
} | ||
} | ||
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impl<T: Sized> Drop for OwnedSlice<T> { | ||
#[inline] | ||
fn drop(&mut self) { | ||
if self.len != 0 { | ||
let _ = mem::replace(self, Self::default()).into_vec(); | ||
} | ||
} | ||
} | ||
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unsafe impl<T: Sized + Send> Send for OwnedSlice<T> {} | ||
unsafe impl<T: Sized + Sync> Sync for OwnedSlice<T> {} | ||
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impl<T: Clone> Clone for OwnedSlice<T> { | ||
#[inline] | ||
fn clone(&self) -> Self { | ||
Self::from_slice(&**self) | ||
} | ||
} | ||
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impl<T: fmt::Debug> fmt::Debug for OwnedSlice<T> { | ||
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { | ||
self.deref().fmt(formatter) | ||
} | ||
} | ||
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impl<T: PartialEq> PartialEq for OwnedSlice<T> { | ||
fn eq(&self, other: &Self) -> bool { | ||
self.deref().eq(other.deref()) | ||
} | ||
} | ||
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impl<T: Eq> Eq for OwnedSlice<T> {} | ||
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impl<T: Sized> OwnedSlice<T> { | ||
/// Convert the OwnedSlice into a boxed slice. | ||
#[inline] | ||
pub fn into_box(self) -> Box<[T]> { | ||
self.into_vec().into_boxed_slice() | ||
} | ||
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/// Convert the OwnedSlice into a Vec. | ||
#[inline] | ||
pub fn into_vec(self) -> Vec<T> { | ||
let ret = unsafe { | ||
Vec::from_raw_parts(self.ptr.as_ptr(), self.len, self.len) | ||
}; | ||
mem::forget(self); | ||
ret | ||
} | ||
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/// Iterate over all the elements in the slice taking ownership of them. | ||
#[inline] | ||
pub fn into_iter(self) -> impl Iterator<Item = T> { | ||
self.into_vec().into_iter() | ||
} | ||
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/// Convert the regular slice into an owned slice. | ||
#[inline] | ||
pub fn from_slice(s: &[T]) -> Self | ||
where | ||
T: Clone, | ||
{ | ||
Self::from(s.to_vec()) | ||
} | ||
} | ||
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impl<T> Deref for OwnedSlice<T> { | ||
type Target = [T]; | ||
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#[inline(always)] | ||
fn deref(&self) -> &Self::Target { | ||
unsafe { slice::from_raw_parts(self.ptr.as_ptr(), self.len) } | ||
} | ||
} | ||
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impl<T> DerefMut for OwnedSlice<T> { | ||
#[inline(always)] | ||
fn deref_mut(&mut self) -> &mut Self::Target { | ||
unsafe { slice::from_raw_parts_mut(self.ptr.as_ptr(), self.len) } | ||
} | ||
} | ||
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impl<T> From<Box<[T]>> for OwnedSlice<T> { | ||
#[inline] | ||
fn from(mut b: Box<[T]>) -> Self { | ||
let len = b.len(); | ||
let ptr = unsafe { NonNull::new_unchecked(b.as_mut_ptr()) }; | ||
mem::forget(b); | ||
Self { | ||
len, | ||
ptr, | ||
_phantom: PhantomData, | ||
} | ||
} | ||
} | ||
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impl<T> From<Vec<T>> for OwnedSlice<T> { | ||
#[inline] | ||
fn from(b: Vec<T>) -> Self { | ||
Self::from(b.into_boxed_slice()) | ||
} | ||
} | ||
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impl<T: Sized> MallocShallowSizeOf for OwnedSlice<T> { | ||
fn shallow_size_of(&self, ops: &mut MallocSizeOfOps) -> usize { | ||
unsafe { ops.malloc_size_of(self.ptr.as_ptr()) } | ||
} | ||
} | ||
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impl<T: MallocSizeOf + Sized> MallocSizeOf for OwnedSlice<T> { | ||
fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize { | ||
self.shallow_size_of(ops) + (**self).size_of(ops) | ||
} | ||
} | ||
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impl<T: ToShmem + Sized> ToShmem for OwnedSlice<T> { | ||
fn to_shmem(&self, builder: &mut SharedMemoryBuilder) -> mem::ManuallyDrop<Self> { | ||
unsafe { | ||
let dest = to_shmem::to_shmem_slice(self.iter(), builder); | ||
mem::ManuallyDrop::new(Self::from(Box::from_raw(dest))) | ||
} | ||
} | ||
} |
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