#![allow(unsafe_code)]
use std::{
fmt::{self, Debug},
ops::Deref,
sync::atomic::Ordering::{AcqRel, Acquire, Release},
};
use crossbeam_epoch::{unprotected, Atomic, Guard, Owned, Shared};
use crate::debug_delay;
type CompareAndSwapResult<'g, T> =
Result<Shared<'g, Node<T>>, (Shared<'g, Node<T>>, Owned<Node<T>>)>;
#[derive(Debug)]
pub struct Node<T: Send + 'static> {
pub(crate) inner: T,
pub(crate) next: Atomic<Node<T>>,
}
impl<T: Send + 'static> Drop for Node<T> {
fn drop(&mut self) {
unsafe {
let next = self.next.load(Acquire, unprotected());
if !next.as_raw().is_null() {
drop(next.into_owned());
}
}
}
}
pub struct Stack<T: Send + 'static> {
head: Atomic<Node<T>>,
}
impl<T: Send + 'static> Default for Stack<T> {
fn default() -> Self {
Self { head: Atomic::null() }
}
}
impl<T: Send + 'static> Drop for Stack<T> {
fn drop(&mut self) {
unsafe {
let curr = self.head.load(Acquire, unprotected());
if !curr.as_raw().is_null() {
drop(curr.into_owned());
}
}
}
}
impl<T> Debug for Stack<T>
where
T: Clone + Debug + Send + 'static + Sync,
{
fn fmt(
&self,
formatter: &mut fmt::Formatter<'_>,
) -> Result<(), fmt::Error> {
let guard = crossbeam_epoch::pin();
let head = self.head(&guard);
let iter = StackIter::from_ptr(head, &guard);
formatter.write_str("Stack [")?;
let mut written = false;
for node in iter {
if written {
formatter.write_str(", ")?;
}
formatter.write_str(&*format!("({:?}) ", &node))?;
node.fmt(formatter)?;
written = true;
}
formatter.write_str("]")?;
Ok(())
}
}
impl<T: Send + 'static> Deref for Node<T> {
type Target = T;
fn deref(&self) -> &T {
&self.inner
}
}
impl<T: Clone + Send + Sync + 'static> Stack<T> {
pub fn push(&self, inner: T, guard: &Guard) {
debug_delay();
let node = Owned::new(Node { inner, next: Atomic::null() });
unsafe {
let node = node.into_shared(guard);
loop {
let head = self.head(guard);
node.deref().next.store(head, Release);
if self.head.compare_and_set(head, node, Release, guard).is_ok()
{
return;
}
}
}
}
#[cfg(any(test, feature = "event_log"))]
pub(crate) fn pop(&self, guard: &Guard) -> Option<T> {
use std::ptr;
use std::sync::atomic::Ordering::SeqCst;
debug_delay();
let mut head = self.head(guard);
loop {
match unsafe { head.as_ref() } {
Some(h) => {
let next = h.next.load(Acquire, guard);
match self.head.compare_and_set(head, next, Release, guard)
{
Ok(_) => unsafe {
h.next.store(Shared::default(), SeqCst);
guard.defer_destroy(head);
return Some(ptr::read(&h.inner));
},
Err(h) => head = h.current,
}
}
None => return None,
}
}
}
pub fn cap_node<'g>(
&self,
old: Shared<'_, Node<T>>,
mut node: Owned<Node<T>>,
guard: &'g Guard,
) -> CompareAndSwapResult<'g, T> {
node.next = Atomic::from(old);
let res = self.head.compare_and_set(old, node, AcqRel, guard);
match res {
Err(e) => {
let mut returned = e.new;
returned.next = Atomic::null();
Err((e.current, returned))
}
Ok(success) => Ok(success),
}
}
pub fn cas<'g>(
&self,
old: Shared<'g, Node<T>>,
new: Owned<Node<T>>,
guard: &'g Guard,
) -> CompareAndSwapResult<'g, T> {
debug_delay();
let res = self.head.compare_and_set(old, new, AcqRel, guard);
match res {
Ok(success) => {
if !old.is_null() {
unsafe {
guard.defer_destroy(old);
};
}
Ok(success)
}
Err(e) => Err((e.current, e.new)),
}
}
pub fn head<'g>(&self, guard: &'g Guard) -> Shared<'g, Node<T>> {
self.head.load(Acquire, guard)
}
}
pub struct StackIter<'a, T>
where
T: Send + 'static + Sync,
{
inner: Shared<'a, Node<T>>,
guard: &'a Guard,
}
impl<'a, T> StackIter<'a, T>
where
T: 'a + Send + 'static + Sync,
{
pub fn from_ptr<'b>(
ptr: Shared<'b, Node<T>>,
guard: &'b Guard,
) -> StackIter<'b, T> {
StackIter { inner: ptr, guard }
}
}
impl<'a, T> Iterator for StackIter<'a, T>
where
T: Send + 'static + Sync,
{
type Item = &'a T;
fn next(&mut self) -> Option<Self::Item> {
debug_delay();
if self.inner.is_null() {
None
} else {
unsafe {
let ret = &self.inner.deref().inner;
self.inner = self.inner.deref().next.load(Acquire, self.guard);
Some(ret)
}
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
let mut size = 0;
let mut cursor = self.inner;
while !cursor.is_null() {
unsafe {
cursor = cursor.deref().next.load(Acquire, self.guard);
}
size += 1;
}
(size, Some(size))
}
}
pub fn node_from_frag_vec<T>(from: Vec<T>) -> Owned<Node<T>>
where
T: Send + 'static + Sync,
{
let mut last = None;
for item in from.into_iter().rev() {
last = if let Some(last) = last {
Some(Owned::new(Node { inner: item, next: Atomic::from(last) }))
} else {
Some(Owned::new(Node { inner: item, next: Atomic::null() }))
}
}
last.expect("at least one frag was provided in the from Vec")
}
#[test]
fn basic_functionality() {
use crossbeam_epoch::pin;
use crossbeam_utils::CachePadded;
use std::sync::Arc;
use std::thread;
let guard = pin();
let ll = Arc::new(Stack::default());
assert_eq!(ll.pop(&guard), None);
ll.push(CachePadded::new(1), &guard);
let ll2 = Arc::clone(&ll);
let t = thread::spawn(move || {
let guard = pin();
ll2.push(CachePadded::new(2), &guard);
ll2.push(CachePadded::new(3), &guard);
ll2.push(CachePadded::new(4), &guard);
guard.flush();
});
t.join().unwrap();
ll.push(CachePadded::new(5), &guard);
assert_eq!(ll.pop(&guard), Some(CachePadded::new(5)));
assert_eq!(ll.pop(&guard), Some(CachePadded::new(4)));
let ll3 = Arc::clone(&ll);
let t = thread::spawn(move || {
let guard = pin();
assert_eq!(ll3.pop(&guard), Some(CachePadded::new(3)));
assert_eq!(ll3.pop(&guard), Some(CachePadded::new(2)));
guard.flush();
});
t.join().unwrap();
assert_eq!(ll.pop(&guard), Some(CachePadded::new(1)));
let ll4 = Arc::clone(&ll);
let t = thread::spawn(move || {
let guard = pin();
assert_eq!(ll4.pop(&guard), None);
guard.flush();
});
t.join().unwrap();
drop(ll);
guard.flush();
drop(guard);
}