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// SPDX-License-Identifier: Apache-2.0 OR MIT
#![allow(clippy::undocumented_unsafe_blocks)]
#![cfg_attr(feature = "alloc", feature(allocator_api))]
use core::{
cell::Cell,
convert::Infallible,
marker::PhantomPinned,
pin::Pin,
ptr::{self, NonNull},
};
use pin_init::*;
#[expect(unused_attributes)]
mod error;
use error::Error;
#[pin_data(PinnedDrop)]
#[repr(C)]
#[derive(Debug)]
pub struct ListHead {
next: Link,
prev: Link,
#[pin]
pin: PhantomPinned,
}
impl ListHead {
#[inline]
pub fn new() -> impl PinInit<Self, Infallible> {
try_pin_init!(&this in Self {
next: unsafe { Link::new_unchecked(this) },
prev: unsafe { Link::new_unchecked(this) },
pin: PhantomPinned,
}? Infallible)
}
#[inline]
pub fn insert_next(list: &ListHead) -> impl PinInit<Self, Infallible> + '_ {
try_pin_init!(&this in Self {
prev: list.next.prev().replace(unsafe { Link::new_unchecked(this)}),
next: list.next.replace(unsafe { Link::new_unchecked(this)}),
pin: PhantomPinned,
}? Infallible)
}
#[inline]
pub fn insert_prev(list: &ListHead) -> impl PinInit<Self, Infallible> + '_ {
try_pin_init!(&this in Self {
next: list.prev.next().replace(unsafe { Link::new_unchecked(this)}),
prev: list.prev.replace(unsafe { Link::new_unchecked(this)}),
pin: PhantomPinned,
}? Infallible)
}
#[inline]
pub fn next(&self) -> Option<NonNull<Self>> {
if ptr::eq(self.next.as_ptr(), self) {
None
} else {
Some(unsafe { NonNull::new_unchecked(self.next.as_ptr() as *mut Self) })
}
}
#[allow(dead_code)]
pub fn size(&self) -> usize {
let mut size = 1;
let mut cur = self.next.clone();
while !ptr::eq(self, cur.cur()) {
cur = cur.next().clone();
size += 1;
}
size
}
}
#[pinned_drop]
impl PinnedDrop for ListHead {
//#[inline]
fn drop(self: Pin<&mut Self>) {
if !ptr::eq(self.next.as_ptr(), &*self) {
let next = unsafe { &*self.next.as_ptr() };
let prev = unsafe { &*self.prev.as_ptr() };
next.prev.set(&self.prev);
prev.next.set(&self.next);
}
}
}
#[repr(transparent)]
#[derive(Clone, Debug)]
struct Link(Cell<NonNull<ListHead>>);
impl Link {
/// # Safety
///
/// The contents of the pointer should form a consistent circular
/// linked list; for example, a "next" link should be pointed back
/// by the target `ListHead`'s "prev" link and a "prev" link should be
/// pointed back by the target `ListHead`'s "next" link.
#[inline]
unsafe fn new_unchecked(ptr: NonNull<ListHead>) -> Self {
Self(Cell::new(ptr))
}
#[inline]
fn next(&self) -> &Link {
unsafe { &(*self.0.get().as_ptr()).next }
}
#[inline]
fn prev(&self) -> &Link {
unsafe { &(*self.0.get().as_ptr()).prev }
}
#[allow(dead_code)]
fn cur(&self) -> &ListHead {
unsafe { &*self.0.get().as_ptr() }
}
#[inline]
fn replace(&self, other: Link) -> Link {
unsafe { Link::new_unchecked(self.0.replace(other.0.get())) }
}
#[inline]
fn as_ptr(&self) -> *const ListHead {
self.0.get().as_ptr()
}
#[inline]
fn set(&self, val: &Link) {
self.0.set(val.0.get());
}
}
#[allow(dead_code)]
#[cfg_attr(test, test)]
fn main() -> Result<(), Error> {
let a = Box::pin_init(ListHead::new())?;
stack_pin_init!(let b = ListHead::insert_next(&a));
stack_pin_init!(let c = ListHead::insert_next(&a));
stack_pin_init!(let d = ListHead::insert_next(&b));
let e = Box::pin_init(ListHead::insert_next(&b))?;
println!("a ({a:p}): {a:?}");
println!("b ({b:p}): {b:?}");
println!("c ({c:p}): {c:?}");
println!("d ({d:p}): {d:?}");
println!("e ({e:p}): {e:?}");
let mut inspect = &*a;
while let Some(next) = inspect.next() {
println!("({inspect:p}): {inspect:?}");
inspect = unsafe { &*next.as_ptr() };
if core::ptr::eq(inspect, &*a) {
break;
}
}
Ok(())
}
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