blob: 0c5f9096bf26766d52d3da84ce9bb05785608540 [file] [log] [blame]
use std::sync::atomic::Ordering::{Acquire, Release, Relaxed};
use std::ptr;
use epoch::{self, Atomic, Owned};
/// Treiber's lock-free stack.
///
/// Usable with any number of producers and consumers.
#[derive(Debug)]
pub struct TreiberStack<T> {
head: Atomic<Node<T>>,
}
#[derive(Debug)]
struct Node<T> {
data: T,
next: Atomic<Node<T>>,
}
impl<T> TreiberStack<T> {
/// Create a new, empty stack.
pub fn new() -> TreiberStack<T> {
TreiberStack { head: Atomic::null() }
}
/// Push `t` on top of the stack.
pub fn push(&self, t: T) {
let mut n = Owned::new(Node {
data: t,
next: Atomic::null(),
});
let guard = epoch::pin();
loop {
let head = self.head.load(Relaxed, &guard);
n.next.store_shared(head, Relaxed);
match self.head.cas_and_ref(head, n, Release, &guard) {
Ok(_) => break,
Err(owned) => n = owned,
}
}
}
/// Attempt to pop the top element of the stack.
/// **Deprecated method**, use try_pop
///
/// Returns `None` if the stack is observed to be empty.
#[cfg_attr(any(feature="beta", feature="nightly"), deprecated(note="The pop method has been renamed to try_pop for consistency with other collections."))]
pub fn pop(&self) -> Option<T> {
self.try_pop()
}
/// Attempt to pop the top element of the stack.
///
/// Returns `None` if the stack is observed to be empty.
pub fn try_pop(&self) -> Option<T> {
let guard = epoch::pin();
loop {
match self.head.load(Acquire, &guard) {
Some(head) => {
let next = head.next.load(Relaxed, &guard);
if self.head.cas_shared(Some(head), next, Release) {
unsafe {
guard.unlinked(head);
return Some(ptr::read(&(*head).data));
}
}
}
None => return None,
}
}
}
/// Check if this queue is empty.
pub fn is_empty(&self) -> bool {
let guard = epoch::pin();
self.head.load(Acquire, &guard).is_none()
}
}
impl<T> Drop for TreiberStack<T> {
fn drop(&mut self) {
while self.try_pop().is_some() {}
}
}
impl<T> Default for TreiberStack<T> {
fn default() -> Self {
TreiberStack::new()
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn is_empty() {
let q: TreiberStack<i64> = TreiberStack::new();
assert!(q.is_empty());
q.push(20);
q.push(20);
assert!(!q.is_empty());
assert!(!q.is_empty());
assert!(q.try_pop().is_some());
assert!(q.try_pop().is_some());
assert!(q.is_empty());
q.push(25);
assert!(!q.is_empty());
}
}