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use MaybeUninit to replace Option #1

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merged 1 commit into from
Jan 17, 2024
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use MaybeUninit to replace Option #1

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69 changes: 42 additions & 27 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
#![feature(inline_const)]
use std::{
marker::PhantomData,
mem::offset_of,
mem::{offset_of, MaybeUninit},
ops::{Deref, DerefMut},
pin::Pin,
ptr::{self, NonNull},
Expand All @@ -21,8 +21,8 @@ struct Inner<T> {

/// Intrusive link.
struct ListHead<T> {
prev: Option<NonNull<ListHead<T>>>,
next: Option<NonNull<ListHead<T>>>,
prev: MaybeUninit<NonNull<ListHead<T>>>,
next: MaybeUninit<NonNull<ListHead<T>>>,
dtype: PhantomData<T>,
}

Expand All @@ -32,12 +32,14 @@ impl<T> LinkNode<T> {
let mut node = Self(Box::pin(Inner {
data,
list: ListHead {
prev: None,
next: None,
prev: MaybeUninit::uninit(),
next: MaybeUninit::uninit(),
dtype: PhantomData,
},
}));
node.list_mut().init_head();
unsafe {
node.list_mut().init_head();
}
node
}

Expand All @@ -61,8 +63,10 @@ impl<T> LinkNode<T> {
#[inline]
pub fn take(&mut self) {
let list = self.list_mut();
unsafe { list.delist() };
list.init_head();
unsafe {
list.delist();
list.init_head();
}
}

pub fn for_each<F>(&self, f: F)
Expand Down Expand Up @@ -126,12 +130,17 @@ impl<T> Drop for LinkNode<T> {
}

impl<T> ListHead<T> {
#[inline(always)]
unsafe fn ptr(&mut self) -> NonNull<ListHead<T>> {
NonNull::new_unchecked(self as *mut ListHead<T>)
}

/// Called when node is created.
#[inline(always)]
fn init_head(&mut self) {
let list = NonNull::new(self as *mut ListHead<T>);
self.prev = list;
self.next = list;
unsafe fn init_head(&mut self) {
let self_ptr = self.ptr();
self.prev.write(self_ptr);
self.next.write(self_ptr);
}

/// Unlink the current node from its previous list.
Expand All @@ -144,10 +153,10 @@ impl<T> ListHead<T> {
/// or in `add()` to update to `prev` and `next` pointers.
#[inline(always)]
unsafe fn delist(&mut self) {
let mut prev = self.prev.unwrap();
let mut next = self.next.unwrap();
prev.as_mut().next = Some(next);
next.as_mut().prev = Some(prev);
let mut prev = self.prev.assume_init();
let mut next = self.next.assume_init();
prev.as_mut().next.write(next);
next.as_mut().prev.write(prev);
}

/// Add `other` between `self` and `self.next`.
Expand All @@ -159,22 +168,25 @@ impl<T> ListHead<T> {
/// is still complete.
#[inline(always)]
unsafe fn add(&mut self, other: &mut ListHead<T>) {
other.prev = NonNull::new(self as *mut ListHead<T>);
other.prev.write(self.ptr());
other.next = self.next;
self.next.unwrap().as_mut().prev = NonNull::new(other as *mut ListHead<T>);
self.next = NonNull::new(other as *mut ListHead<T>);

let next = self.next.assume_init_mut().as_mut();
next.prev.write(other.ptr());
self.next.write(other.ptr());
}

#[inline(always)]
fn for_each<F>(&self, mut f: F)
where
F: FnMut(&T),
{
let self_ptr = self as *const Self;
let mut this = self;
loop {
f(this.get());
let next = this.next.unwrap();
if ptr::eq(next.as_ptr(), self) {
let next = unsafe { this.next.assume_init_ref() };
if ptr::eq(next.as_ptr(), self_ptr) {
break;
}
this = unsafe { next.as_ref() };
Expand All @@ -186,11 +198,12 @@ impl<T> ListHead<T> {
where
F: FnMut(&mut T),
{
let self_ptr = self as *const Self;
let mut this = &mut *self;
loop {
f(this.get_mut());
let mut next = this.next.unwrap();
if ptr::eq(next.as_ptr(), self) {
let next = unsafe { this.next.assume_init_mut() };
if ptr::eq(next.as_ptr(), self_ptr) {
break;
}
this = unsafe { next.as_mut() };
Expand All @@ -202,11 +215,12 @@ impl<T> ListHead<T> {
where
F: FnMut(&T),
{
let self_ptr = self as *const Self;
let mut this = self;
loop {
f(this.get());
let prev = this.prev.unwrap();
if ptr::eq(prev.as_ptr(), self) {
let prev = unsafe { this.prev.assume_init_ref() };
if ptr::eq(prev.as_ptr(), self_ptr) {
break;
}
this = unsafe { prev.as_ref() };
Expand All @@ -218,11 +232,12 @@ impl<T> ListHead<T> {
where
F: FnMut(&mut T),
{
let self_ptr = self as *const Self;
let mut this = &mut *self;
loop {
f(this.get_mut());
let mut prev = this.prev.unwrap();
if ptr::eq(prev.as_ptr(), self) {
let prev = unsafe { this.prev.assume_init_mut() };
if ptr::eq(prev.as_ptr(), self_ptr) {
break;
}
this = unsafe { prev.as_mut() };
Expand Down
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