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use std::cell::Cell;
use std::ptr::{NonNull, null_mut};
use std::sync::atomic::{AtomicPtr, Ordering};
#[doc(hidden)]
#[derive(Debug)]
pub struct Head {
tail: AtomicPtr<Link>,
head: Cell<NonNull<Link>>,
stub: Box<Link>,
}
impl Head {
#[allow(clippy::new_without_default)]
pub fn new() -> Self {
let stub = Box::new(Link::new());
Self {
tail: AtomicPtr::new(&*stub as *const Link as *mut _),
head: Cell::new(NonNull::from(&*stub)),
stub,
}
}
pub unsafe fn push(&self, link: *const Link) {
self._push(link);
}
fn _push(&self, link: *const Link) {
let link = link as *mut Link;
let prev = self.tail.swap(link, Ordering::Release);
unsafe { &*prev }.next.store(link, Ordering::Release);
}
#[allow(clippy::mut_from_ref)]
pub unsafe fn start_pop(&self) -> impl Iterator<Item = *const Link> + '_ {
PopAll { this: self, pos: self.head.get(), repushed_stub: false }
}
}
impl Default for Head {
fn default() -> Self {
Self::new()
}
}
impl Drop for Head {
fn drop(&mut self) {
assert_eq!(self.tail.load(Ordering::Relaxed) as *const Link, &*self.stub);
}
}
struct PopAll<'a> {
this: &'a Head,
pos: NonNull<Link>,
repushed_stub: bool,
}
impl Drop for PopAll<'_> {
fn drop(&mut self) {
self.this.head.set(self.pos);
}
}
impl Iterator for PopAll<'_> {
type Item = *const Link;
fn next(&mut self) -> Option<Self::Item> {
loop {
let next = NonNull::new(unsafe { self.pos.as_ref() }.next.swap(null_mut(), Ordering::Acquire))?;
let item = self.pos.as_ptr() as *const Link;
self.pos = next;
if item == &*self.this.stub {
let break_loop = self.repushed_stub;
self.repushed_stub = true;
self.this._push(item);
if break_loop {
return None;
}
} else {
return Some(item);
}
}
}
}
#[doc(hidden)]
#[derive(Debug)]
pub struct Link {
next: AtomicPtr<Link>,
}
impl Link {
pub const fn new() -> Self {
Self {
next: AtomicPtr::new(null_mut()),
}
}
}
impl Default for Link {
fn default() -> Self {
Self::new()
}
}
#[macro_export]
macro_rules! mpsc {
(mod $($tt:tt)*) => {
$crate::_mpsc! {
[pub(self)] [pub(super)] mod $($tt)*
}
};
(pub mod $($tt:tt)*) => {
$crate::_mpsc! {
[pub] [pub] mod $($tt)*
}
};
(pub(crate) mod $($tt:tt)*) => {
$crate::_mpsc! {
[pub(crate)] [pub(crate)] mod $($tt)*
}
};
}
#[doc(hidden)]
#[macro_export]
macro_rules! _mpsc {
([$vis:vis] [$innervis:vis] mod $modname:ident {
link $link_name:ident;
head $head_name:ident;
member $member:ident of $parent:ident;
}) => {
mod $modname {
use std::sync::Arc;
use $crate::mpsc::{Link, Head};
use super::$parent;
#[derive(Debug, Default)]
$innervis struct $link_name {
link: Link,
}
unsafe impl Sync for $link_name {}
unsafe impl Send for $link_name {}
impl $link_name {
#[allow(dead_code)]
$innervis const fn new() -> Self {
Self {
link: Link::new(),
}
}
fn __base_from_node(ptr: *const Link) -> *const $parent {
let member_offset: usize = {
let p = core::ptr::NonNull::<$parent>::dangling();
let $parent { $member: member, .. } = unsafe { &*p.as_ptr() };
let head: &Link = &(member as &Self).link;
(head as *const _ as usize) - (p.as_ptr() as *const _ as usize)
};
unsafe { (ptr as *const u8).sub(member_offset) as *const $parent }
}
}
#[derive(Debug)]
$innervis struct $head_name {
head: Head,
}
unsafe impl Sync for $head_name {}
unsafe impl Send for $head_name {}
impl $head_name {
#[allow(dead_code)]
$innervis fn new() -> Self {
Self {
head: Head::new(),
}
}
$innervis fn push(&self, node: Arc<$parent>) {
use core::mem::ManuallyDrop;
let node = ManuallyDrop::new(node);
let node_link: &$link_name = &(*node).$member;
unsafe { self.head.push(&node_link.link); }
}
$innervis unsafe fn start_pop(&self) -> impl Iterator<Item = Arc<$parent>> + '_ {
self.head.start_pop().map(|item| {
Arc::from_raw($link_name::__base_from_node(item))
})
}
}
impl Default for $head_name {
fn default() -> Self {
Self::new()
}
}
impl Drop for $head_name {
fn drop(&mut self) {
for _ in unsafe { self.start_pop() } {}
}
}
}
$vis use self::$modname::{$link_name, $head_name};
};
}
#[cfg(test)]
mod test {
use std::sync::Arc;
mpsc! {
mod ex1 {
link MyLink;
head MyHead;
member my_link of MyData;
}
}
struct MyData {
my_link: MyLink,
value: u32,
}
impl MyData {
fn new(value: u32) -> Self {
Self {
my_link: MyLink::default(),
value,
}
}
}
#[test]
fn twoitems() {
let list = MyHead::new();
let data1 = Arc::new(MyData::new(1));
let data2 = Arc::new(MyData::new(2));
list.push(data1);
list.push(data2);
let mut counter = 1;
for item in unsafe { list.start_pop() } {
assert_eq!(counter, item.value);
counter += 1;
}
}
}