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use crate::fib::FiberRoot;
use core::{
pin::Pin,
ptr,
sync::atomic::{AtomicPtr, Ordering},
};
pub struct Chain {
head: AtomicPtr<Node>,
}
struct Node {
fib: Pin<Box<dyn FiberRoot>>,
next: *mut Node,
}
impl Chain {
pub const fn new() -> Self {
Self {
head: AtomicPtr::new(ptr::null_mut()),
}
}
pub fn add<F: FiberRoot>(&self, fib: F) {
self.push(Node::new(fib));
}
pub fn is_empty(&self) -> bool {
self.head.load(Ordering::Acquire).is_null()
}
#[inline(never)]
pub unsafe fn drain(&self) {
let mut prev = ptr::null_mut();
let mut curr = self.head.load(Ordering::Acquire);
while !curr.is_null() {
let next = (*curr).next;
if (*curr).fib.as_mut().advance() {
prev = curr;
} else {
if prev.is_null() {
prev = self.head.compare_and_swap(curr, next, Ordering::Relaxed);
if prev == curr {
prev = ptr::null_mut();
} else {
loop {
prev = (*prev).next;
if prev == curr {
(*prev).next = next;
break;
}
}
}
} else {
(*prev).next = next;
}
drop(Box::from_raw(curr));
}
curr = next;
}
}
fn push(&self, node: Node) {
let node = Box::into_raw(Box::new(node));
loop {
let head = self.head.load(Ordering::Relaxed);
unsafe { (*node).next = head };
if self.head.compare_and_swap(head, node, Ordering::Release) == head {
break;
}
}
}
}
impl Node {
fn new<F: FiberRoot>(fib: F) -> Self {
Self {
fib: Box::pin(fib),
next: ptr::null_mut(),
}
}
}