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use std::cmp::max;
use std::mem::MaybeUninit;
use std::sync::atomic::{AtomicI8, AtomicUsize, Ordering};
#[warn(missing_docs)]
enum CellState {
Empty = 0,
Storing = 1,
Stored = 2,
Loading = 3,
}
impl From<CellState> for i8 {
fn from(value: CellState) -> Self {
match value {
CellState::Empty => 0,
CellState::Storing => 1,
CellState::Stored => 2,
CellState::Loading => 3,
}
}
}
pub struct Queue<T> {
head: AtomicUsize,
tail: AtomicUsize,
elements: Vec<MaybeUninit<T>>,
states: Vec<AtomicI8>,
}
unsafe impl<T: Send> Send for Queue<T> {}
unsafe impl<T> Sync for Queue<T> {}
pub fn bounded<T>(capacity: usize) -> Queue<T> {
Queue::new(capacity)
}
impl<T> Queue<T> {
pub fn new(capacity: usize) -> Self {
let mut elements = Vec::with_capacity(capacity);
for _ in 0..capacity {
elements.push(MaybeUninit::uninit());
}
let mut states = Vec::with_capacity(capacity);
for _ in 0..capacity {
states.push(AtomicI8::new(CellState::Empty.into()));
}
let head = AtomicUsize::new(0);
let tail = AtomicUsize::new(0);
Queue {
head,
tail,
elements,
states,
}
}
pub fn push(&self, element: T) -> bool {
let mut head = self.head.load(Ordering::Relaxed);
let elements_len = self.elements.len();
loop {
let length = head as i64 - self.tail.load(Ordering::Relaxed) as i64;
if length >= elements_len as i64 {
return false;
}
if self
.head
.compare_exchange(head, head + 1, Ordering::Acquire, Ordering::Relaxed)
.is_ok()
{
self.do_push(element, head);
return true;
}
head = self.head.load(Ordering::Relaxed);
}
}
pub fn pop(&self) -> Option<T> {
let mut tail = self.tail.load(Ordering::Relaxed);
loop {
let length = self.head.load(Ordering::Relaxed) as i64 - tail as i64;
if length <= 0 {
return None;
}
if self
.tail
.compare_exchange(tail, tail + 1, Ordering::Acquire, Ordering::Relaxed)
.is_ok()
{
break;
}
tail = self.tail.load(Ordering::Relaxed);
}
Some(self.do_pop(tail))
}
pub unsafe fn force_pop(&self) -> T {
let tail = self.tail.fetch_add(1, Ordering::Acquire);
self.do_pop(tail)
}
pub unsafe fn force_push(&self, element: T) {
let head = self.head.fetch_add(1, Ordering::Acquire);
self.do_push(element, head);
}
pub fn is_empty(&self) -> bool {
self.len() == 0
}
pub fn len(&self) -> usize {
max(
self.head.load(Ordering::Relaxed) - self.tail.load(Ordering::Relaxed),
0,
)
}
}
impl<T> Queue<T> {
fn do_pop(&self, tail: usize) -> T {
let state = &self.states[tail % self.states.len()];
loop {
let expected = CellState::Stored;
if state
.compare_exchange(
expected.into(),
CellState::Loading.into(),
Ordering::Acquire,
Ordering::Relaxed,
)
.is_ok()
{
let self_ptr = self as *const Self as *mut Self;
let element = unsafe {
std::mem::replace(
&mut (*self_ptr).elements[tail % self.elements.len()],
MaybeUninit::uninit(),
)
};
state.store(CellState::Empty.into(), Ordering::Release);
return unsafe { element.assume_init() };
}
}
}
fn do_push(&self, element: T, head: usize) {
self.do_push_any(element, head);
}
fn do_push_any(&self, element: T, head: usize) {
let state = &self.states[head % self.states.len()];
loop {
let expected = CellState::Empty;
if state
.compare_exchange(
expected.into(),
CellState::Storing.into(),
Ordering::Acquire,
Ordering::Relaxed,
)
.is_ok()
{
unsafe {
let self_ptr = self as *const Self as *mut Self;
(*self_ptr).elements[head % self.elements.len()] = MaybeUninit::new(element);
}
state.store(CellState::Stored.into(), Ordering::Release);
return;
}
}
}
}
#[cfg(test)]
mod test {
use std::ffi::c_void;
use std::sync::{Arc, Mutex};
use std::thread;
use std::thread::JoinHandle;
use std::time::Duration;
use super::*;
#[derive(Eq, PartialEq, Debug, Copy, Clone)]
struct MockPtr(*mut c_void);
unsafe impl Send for MockPtr {}
fn mock_ptr(value: i32) -> MockPtr {
MockPtr(value as *mut c_void)
}
#[test]
fn test_create_bounded_queue() {
let _queue = Queue::<MockPtr>::new(10);
}
#[test]
fn test_get_empty_queue_len() {
let queue = Queue::<MockPtr>::new(10);
assert_eq!(queue.len(), 0);
}
#[test]
fn test_push_element_to_queue_increments_length() {
let queue = Queue::<MockPtr>::new(10);
assert_eq!(queue.len(), 0);
let ptr = mock_ptr(1);
assert!(queue.push(ptr));
assert_eq!(queue.len(), 1);
let value = queue.pop();
assert_eq!(value.unwrap(), ptr);
assert_eq!(queue.len(), 0);
}
#[test]
fn test_push_pop_push_pop() {
let queue = Queue::<MockPtr>::new(10);
assert_eq!(queue.len(), 0);
{
let ptr = mock_ptr(1);
assert!(queue.push(ptr));
assert_eq!(queue.len(), 1);
let value = queue.pop();
assert_eq!(value.unwrap(), ptr);
assert_eq!(queue.len(), 0);
}
{
let ptr = mock_ptr(2);
assert!(queue.push(ptr));
assert_eq!(queue.len(), 1);
let value = queue.pop();
assert_eq!(value.unwrap(), ptr);
assert_eq!(queue.len(), 0);
}
}
#[test]
fn test_overflow_will_not_break_things() {
let queue = Queue::<MockPtr>::new(3);
assert_eq!(queue.len(), 0);
assert!(queue.push(mock_ptr(1)));
assert_eq!(queue.len(), 1);
assert!(queue.push(mock_ptr(2)));
assert_eq!(queue.len(), 2);
assert!(queue.push(mock_ptr(3)));
assert_eq!(queue.len(), 3);
assert_eq!(queue.len(), 3);
let result = queue.push(mock_ptr(4));
assert!(!result);
assert_eq!(queue.len(), 3);
}
#[test]
fn test_multithread_push() {
wisual_logger::init_from_env();
let queue = Arc::new(Queue::new(50000));
let writer_thread_1 = spawn_writer_thread(
10,
queue.clone(),
Duration::from_millis((0.0 * rand::random::<f64>()) as u64),
);
let writer_thread_2 = spawn_writer_thread(
10,
queue.clone(),
Duration::from_millis((0.0 * rand::random::<f64>()) as u64),
);
let writer_thread_3 = spawn_writer_thread(
10,
queue.clone(),
Duration::from_millis((0.0 * rand::random::<f64>()) as u64),
);
writer_thread_1.join().unwrap();
writer_thread_2.join().unwrap();
writer_thread_3.join().unwrap();
assert_eq!(queue.len(), 30);
}
#[test]
fn test_multithread_push_pop() {
wisual_logger::init_from_env();
let size = 10000;
let num_threads = 5;
let queue: Arc<Queue<MockPtr>> = Arc::new(Queue::new(size * num_threads / 3));
let output_queue: Arc<Queue<MockPtr>> = Arc::new(Queue::new(size * num_threads));
let is_running = Arc::new(Mutex::new(true));
let reader_thread = {
let is_running = is_running.clone();
let queue = queue.clone();
let output_queue = output_queue.clone();
thread::spawn(move || {
while *is_running.lock().unwrap() || queue.len() > 0 {
loop {
match queue.pop() {
None => break,
Some(value) => {
output_queue.push(value);
}
}
}
}
log::info!("Reader thread done reading");
})
};
let threads: Vec<JoinHandle<()>> = (0..num_threads)
.into_iter()
.map(|_| {
spawn_writer_thread(
size,
queue.clone(),
Duration::from_millis((rand::random::<f64>()) as u64),
)
})
.collect();
for thread in threads {
thread.join().unwrap();
}
{
let mut is_running = is_running.lock().unwrap();
*is_running = false;
}
reader_thread.join().unwrap();
assert_eq!(queue.len(), 0);
assert_eq!(output_queue.len(), size * num_threads);
}
fn spawn_writer_thread(
size: usize,
queue: Arc<Queue<MockPtr>>,
duration: Duration,
) -> JoinHandle<()> {
thread::spawn(move || {
for i in 0..size {
loop {
let pushed = queue.push(mock_ptr(i as i32));
if pushed {
break;
}
}
thread::sleep(duration);
}
log::info!("Thread done writing");
})
}
}