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version: 2
updates:
- package-ecosystem: "cargo"
directory: "/"
schedule:
interval: "daily"

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on: [pull_request]
name: lint
jobs:
fmt:
name: cargo fmt
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v2
- uses: actions-rs/toolchain@v1
with:
components: rustfmt
toolchain: nightly
profile: minimal
override: true
- uses: actions-rs/cargo@v1
with:
command: fmt
args: --all -- --check
clippy:
name: cargo clippy
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v2
- uses: actions-rs/toolchain@v1
with:
components: clippy
toolchain: nightly
profile: minimal
override: true
- uses: actions-rs/cargo@v1
with:
command: clippy
args: -- -D warnings
readme:
name: cargo readme
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v2
- uses: actions-rs/toolchain@v1
with:
toolchain: nightly
profile: minimal
override: true
- run: cargo install cargo-readme
- run: cargo readme > README.md && git diff --exit-code

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on: [pull_request]
name: test
jobs:
test:
name: ${{ matrix.toolchain }} (${{ matrix.profile.name }})
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v2
- uses: actions-rs/toolchain@v1
with:
toolchain: ${{ matrix.toolchain }}
override: true
- uses: actions-rs/cargo@v1
with:
command: test
args: ${{ matrix.profile.flag }}
strategy:
fail-fast: false
matrix:
toolchain:
- nightly
profile:
- name: debug
- name: release
flag: --release

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/.idea
/target
Cargo.lock

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Cargo.toml Normal file
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[package]
name = "slabvec"
version = "0.1.0"
authors = ["Harald Hoyer <harald@redhat.com>"]
edition = "2018"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]

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README.md Normal file
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# slabvec
Array of `T` with dynamic allocations of `N` entries for slabs of size `M`
The array will dynamically allocate slabs of size `M` to extend its internal
linked list, which will extend the capacity by `N`.
Currently nightly until `#![feature(min_const_generics)]` hits stable with `1.51`.

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nightly

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src/lib.rs Normal file
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// SPDX-License-Identifier: Apache-2.0
//! Array of `T` with dynamic allocations of `N` entries for slabs of size `M`
//!
//! The array will dynamically allocate slabs of size `M` to extend its internal
//! linked list, which will extend the capacity by `N`.
//!
//! Currently nightly until `#![feature(min_const_generics)]` hits stable with `1.51`.
#![deny(missing_docs)]
#![deny(clippy::all)]
#![cfg_attr(not(test), no_std)]
use core::alloc::GlobalAlloc;
use core::alloc::Layout;
use core::marker::PhantomData;
use core::mem::{align_of, size_of, MaybeUninit};
use core::ptr::NonNull;
#[inline]
const fn align_up<T>(addr: usize) -> usize {
let align_mask = align_of::<T>() - 1;
if addr & align_mask == 0 {
addr // already aligned
} else {
(addr | align_mask) + 1
}
}
/// Array of `T` with dynamic allocations of `N` entries for slabs of size `M`
pub struct SlabVec<T: Default + Copy + Sized, const N: usize, const M: usize> {
head: Option<NonNull<ListPage<T, N, M>>>,
tail: Option<NonNull<ListPage<T, N, M>>>,
len: usize,
alloc: &'static dyn GlobalAlloc,
}
impl<T: Default + Copy + Sized, const N: usize, const M: usize> SlabVec<T, N, M> {
/// Number of entries a [`SlabVec`] could hold
///
/// Trick used because of const_generics being still unstable.
pub const NUM_ENTRIES: usize =
(M - size_of::<ListPageHeader<T, N, 1>>()) / align_up::<T>(size_of::<T>());
/// Get a new List using `alloc` as the allocator for its slabs
pub fn new(alloc: &'static dyn GlobalAlloc) -> Self {
let mut sl = Self {
alloc,
len: 0,
head: None,
tail: None,
};
sl.add_page();
sl
}
/// Add one more page of size `M` with `N` entries
pub fn add_page(&mut self) {
let lp = NonNull::new({
let ele = unsafe {
&mut *(self
.alloc
.alloc(Layout::from_size_align(M, align_of::<ListPage<T, N, M>>()).unwrap())
as *mut MaybeUninit<ListPage<T, N, M>>)
};
unsafe {
ele.as_mut_ptr().write(ListPage::<T, N, M> {
header: ListPageHeader { next: None },
entry: [T::default(); N],
});
// As the yet unstable MaybeUninit::assume_init_mut()
&mut *ele.as_mut_ptr()
}
});
if self.head.is_none() {
self.head = lp;
}
if let Some(mut tail) = self.tail {
unsafe { tail.as_mut() }.header.next = lp;
}
self.tail = lp;
self.len += N;
}
/// Provides a forward iterator.
pub fn iter(&self) -> Iter<'_, T, N, M> {
Iter {
current: self.head,
index: 0,
len: self.len,
phantom: PhantomData,
}
}
/// Provides a forward iterator with mutable references.
pub fn iter_mut(&mut self) -> IterMut<'_, T, N, M> {
IterMut {
current: self.head,
index: 0,
len: self.len,
phantom: PhantomData,
}
}
}
impl<T: Default + Copy + Sized, const N: usize, const M: usize> Drop for SlabVec<T, N, M> {
fn drop(&mut self) {
unsafe {
let mut this = self.head.take();
while let Some(mut ele) = this {
this = ele.as_mut().header.next.take();
self.alloc.dealloc(
ele.as_ptr() as *mut u8,
Layout::from_size_align(size_of::<Self>(), align_of::<Self>()).unwrap(),
);
}
}
}
}
#[repr(C)]
struct ListPageHeader<T: Default + Copy + Sized, const N: usize, const M: usize> {
next: Option<NonNull<ListPage<T, N, M>>>,
}
#[repr(C)]
struct ListPage<T: Default + Copy + Sized, const N: usize, const M: usize> {
header: ListPageHeader<T, N, M>,
entry: [T; N],
}
/// An iterator over the elements of a `SlabVec`.
///
/// This `struct` is created by [`SlabVec::iter()`]. See its
/// documentation for more.
pub struct Iter<'a, T: Default + Copy + Sized, const N: usize, const M: usize> {
current: Option<NonNull<ListPage<T, N, M>>>,
index: usize,
len: usize,
phantom: PhantomData<&'a SlabVec<T, N, M>>,
}
impl<'a, T: Default + Copy + Sized, const N: usize, const M: usize> Iterator for Iter<'a, T, N, M> {
type Item = &'a T;
fn next(&mut self) -> Option<Self::Item> {
let this: &ListPage<T, N, M> = unsafe { &*(self.current?.as_ptr()) };
let ret = this.entry.get(self.index)?;
self.len -= 1;
self.index += 1;
if self.index == N {
self.current = this.header.next;
self.index = 0;
}
Some(ret)
}
fn size_hint(&self) -> (usize, Option<usize>) {
(self.len, Some(self.len))
}
}
/// A mutable iterator over the elements of a `SlabVec`.
///
/// This `struct` is created by [`SlabVec::iter_mut()`]. See its
/// documentation for more.
pub struct IterMut<'a, T: Default + Copy + Sized, const N: usize, const M: usize> {
current: Option<NonNull<ListPage<T, N, M>>>,
index: usize,
len: usize,
phantom: PhantomData<&'a mut SlabVec<T, N, M>>,
}
impl<'a, T: Default + Copy + Sized, const N: usize, const M: usize> Iterator
for IterMut<'a, T, N, M>
{
type Item = &'a mut T;
fn next(&mut self) -> Option<Self::Item> {
let this: &mut ListPage<T, N, M> = unsafe { &mut *(self.current?.as_ptr()) };
let ret = this.entry.get_mut(self.index)?;
self.len -= 1;
self.index += 1;
if self.index == N {
self.current = this.header.next;
self.index = 0;
}
Some(ret)
}
fn size_hint(&self) -> (usize, Option<usize>) {
(self.len, Some(self.len))
}
}
#[cfg(test)]
mod tests {
use crate::SlabVec;
const PAGE_SIZE: usize = 4096;
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
#[repr(align(16))]
struct Data {
a: i32,
b: i32,
c: u64,
}
impl Default for Data {
fn default() -> Self {
Self { a: -1, b: -1, c: 0 }
}
}
type DataPageList = SlabVec<Data, { SlabVec::<Data, 1, PAGE_SIZE>::NUM_ENTRIES }, PAGE_SIZE>;
#[test]
fn len() {
static mut SYSTEM: std::alloc::System = std::alloc::System;
let pl = DataPageList::new(unsafe { &mut SYSTEM });
assert_eq!(pl.iter().count(), 255);
}
#[test]
fn const_len() {
assert_eq!(DataPageList::NUM_ENTRIES, 255);
}
#[test]
fn zero_len() {
assert_eq!(
SlabVec::<Data, { SlabVec::<Data, 1, 16>::NUM_ENTRIES }, 16>::NUM_ENTRIES,
0
);
}
#[test]
fn iter() {
static mut SYSTEM: std::alloc::System = std::alloc::System;
let pl = DataPageList::new(unsafe { &mut SYSTEM });
for entry in pl.iter() {
assert_eq!(*entry, Data::default());
}
}
#[test]
fn iter_mut() {
static mut SYSTEM: std::alloc::System = std::alloc::System;
let mut pl = DataPageList::new(unsafe { &mut SYSTEM });
for (i, entry) in pl.iter_mut().enumerate() {
*entry = Data {
a: i as _,
b: i as _,
c: i as _,
};
}
for (i, entry) in pl.iter().enumerate() {
assert_eq!(entry.a, i as _);
assert_eq!(entry.b, i as _);
assert_eq!(entry.c, i as _);
}
}
}