use std::{
collections::VecDeque,
fmt,
iter::FusedIterator,
sync::{Arc, atomic::AtomicUsize},
};
use rand::{RngExt, SeedableRng, rngs::SmallRng};
use crate::Priority;
struct PriorityQueues<T> {
high_priority: VecDeque<T>,
medium_priority: VecDeque<T>,
low_priority: VecDeque<T>,
}
impl<T> PriorityQueues<T> {
fn is_empty(&self) -> bool {
self.high_priority.is_empty()
&& self.medium_priority.is_empty()
&& self.low_priority.is_empty()
}
}
struct PriorityQueueState<T> {
queues: parking_lot::Mutex<PriorityQueues<T>>,
condvar: parking_lot::Condvar,
receiver_count: AtomicUsize,
sender_count: AtomicUsize,
}
impl<T> PriorityQueueState<T> {
fn send(&self, priority: Priority, item: T) -> Result<(), SendError<T>> {
if self
.receiver_count
.load(std::sync::atomic::Ordering::Relaxed)
== 0
{
return Err(SendError(item));
}
let mut queues = self.queues.lock();
Self::push(&mut queues, priority, item);
self.condvar.notify_one();
Ok(())
}
fn spin_send(&self, priority: Priority, item: T) -> Result<(), SendError<T>> {
if self
.receiver_count
.load(std::sync::atomic::Ordering::Relaxed)
== 0
{
return Err(SendError(item));
}
let mut queues = loop {
if let Some(guard) = self.queues.try_lock() {
break guard;
}
std::hint::spin_loop();
};
Self::push(&mut queues, priority, item);
self.condvar.notify_one();
Ok(())
}
fn push(queues: &mut PriorityQueues<T>, priority: Priority, item: T) {
match priority {
Priority::RealtimeAudio => unreachable!(
"Realtime audio priority runs on a dedicated thread and is never queued"
),
Priority::High => queues.high_priority.push_back(item),
Priority::Medium => queues.medium_priority.push_back(item),
Priority::Low => queues.low_priority.push_back(item),
};
}
fn recv<'a>(&'a self) -> Result<parking_lot::MutexGuard<'a, PriorityQueues<T>>, RecvError> {
let mut queues = self.queues.lock();
let sender_count = self.sender_count.load(std::sync::atomic::Ordering::Relaxed);
if queues.is_empty() && sender_count == 0 {
return Err(crate::queue::RecvError);
}
while queues.is_empty() {
self.condvar.wait(&mut queues);
}
Ok(queues)
}
fn try_recv<'a>(
&'a self,
) -> Result<Option<parking_lot::MutexGuard<'a, PriorityQueues<T>>>, RecvError> {
let mut queues = self.queues.lock();
let sender_count = self.sender_count.load(std::sync::atomic::Ordering::Relaxed);
if queues.is_empty() && sender_count == 0 {
return Err(crate::queue::RecvError);
}
if queues.is_empty() {
Ok(None)
} else {
Ok(Some(queues))
}
}
fn spin_try_recv<'a>(
&'a self,
) -> Result<Option<parking_lot::MutexGuard<'a, PriorityQueues<T>>>, RecvError> {
let queues = loop {
if let Some(guard) = self.queues.try_lock() {
break guard;
}
std::hint::spin_loop();
};
let sender_count = self.sender_count.load(std::sync::atomic::Ordering::Relaxed);
if queues.is_empty() && sender_count == 0 {
return Err(crate::queue::RecvError);
}
if queues.is_empty() {
Ok(None)
} else {
Ok(Some(queues))
}
}
}
#[doc(hidden)]
pub struct PriorityQueueSender<T> {
state: Arc<PriorityQueueState<T>>,
}
impl<T> PriorityQueueSender<T> {
fn new(state: Arc<PriorityQueueState<T>>) -> Self {
Self { state }
}
pub fn send(&self, priority: Priority, item: T) -> Result<(), SendError<T>> {
self.state.send(priority, item)?;
Ok(())
}
pub fn spin_send(&self, priority: Priority, item: T) -> Result<(), SendError<T>> {
self.state.spin_send(priority, item)?;
Ok(())
}
}
impl<T> Drop for PriorityQueueSender<T> {
fn drop(&mut self) {
self.state
.sender_count
.fetch_sub(1, std::sync::atomic::Ordering::AcqRel);
}
}
#[doc(hidden)]
pub struct PriorityQueueReceiver<T> {
state: Arc<PriorityQueueState<T>>,
rand: SmallRng,
disconnected: bool,
}
impl<T> Clone for PriorityQueueReceiver<T> {
fn clone(&self) -> Self {
self.state
.receiver_count
.fetch_add(1, std::sync::atomic::Ordering::AcqRel);
Self {
state: Arc::clone(&self.state),
rand: SmallRng::seed_from_u64(0),
disconnected: self.disconnected,
}
}
}
#[doc(hidden)]
pub struct SendError<T>(pub T);
impl<T: fmt::Debug> fmt::Debug for SendError<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("SendError").field(&self.0).finish()
}
}
#[derive(Debug)]
#[doc(hidden)]
pub struct RecvError;
#[allow(dead_code)]
impl<T> PriorityQueueReceiver<T> {
pub fn new() -> (PriorityQueueSender<T>, Self) {
let state = PriorityQueueState {
queues: parking_lot::Mutex::new(PriorityQueues {
high_priority: VecDeque::new(),
medium_priority: VecDeque::new(),
low_priority: VecDeque::new(),
}),
condvar: parking_lot::Condvar::new(),
receiver_count: AtomicUsize::new(1),
sender_count: AtomicUsize::new(1),
};
let state = Arc::new(state);
let sender = PriorityQueueSender::new(Arc::clone(&state));
let receiver = PriorityQueueReceiver {
state,
rand: SmallRng::seed_from_u64(0),
disconnected: false,
};
(sender, receiver)
}
pub fn is_empty(&self) -> bool {
self.state.queues.lock().is_empty()
}
pub fn try_pop(&mut self) -> Result<Option<T>, RecvError> {
self.pop_inner(false)
}
pub fn spin_try_pop(&mut self) -> Result<Option<T>, RecvError> {
use Priority as P;
let Some(mut queues) = self.state.spin_try_recv()? else {
return Ok(None);
};
let high = P::High.weight() * !queues.high_priority.is_empty() as u32;
let medium = P::Medium.weight() * !queues.medium_priority.is_empty() as u32;
let low = P::Low.weight() * !queues.low_priority.is_empty() as u32;
let mut mass = high + medium + low;
if !queues.high_priority.is_empty() {
let flip = self.rand.random_ratio(P::High.weight(), mass);
if flip {
return Ok(queues.high_priority.pop_front());
}
mass -= P::High.weight();
}
if !queues.medium_priority.is_empty() {
let flip = self.rand.random_ratio(P::Medium.weight(), mass);
if flip {
return Ok(queues.medium_priority.pop_front());
}
mass -= P::Medium.weight();
}
if !queues.low_priority.is_empty() {
let flip = self.rand.random_ratio(P::Low.weight(), mass);
if flip {
return Ok(queues.low_priority.pop_front());
}
}
Ok(None)
}
pub fn pop(&mut self) -> Result<T, RecvError> {
self.pop_inner(true).map(|e| e.unwrap())
}
pub fn try_iter(self) -> TryIter<T> {
TryIter {
receiver: self,
ended: false,
}
}
pub fn iter(self) -> Iter<T> {
Iter(self)
}
#[inline(always)]
fn pop_inner(&mut self, block: bool) -> Result<Option<T>, RecvError> {
use Priority as P;
let mut queues = if !block {
let Some(queues) = self.state.try_recv()? else {
return Ok(None);
};
queues
} else {
self.state.recv()?
};
let high = P::High.weight() * !queues.high_priority.is_empty() as u32;
let medium = P::Medium.weight() * !queues.medium_priority.is_empty() as u32;
let low = P::Low.weight() * !queues.low_priority.is_empty() as u32;
let mut mass = high + medium + low;
if !queues.high_priority.is_empty() {
let flip = self.rand.random_ratio(P::High.weight(), mass);
if flip {
return Ok(queues.high_priority.pop_front());
}
mass -= P::High.weight();
}
if !queues.medium_priority.is_empty() {
let flip = self.rand.random_ratio(P::Medium.weight(), mass);
if flip {
return Ok(queues.medium_priority.pop_front());
}
mass -= P::Medium.weight();
}
if !queues.low_priority.is_empty() {
let flip = self.rand.random_ratio(P::Low.weight(), mass);
if flip {
return Ok(queues.low_priority.pop_front());
}
}
Ok(None)
}
}
impl<T> Drop for PriorityQueueReceiver<T> {
fn drop(&mut self) {
self.state
.receiver_count
.fetch_sub(1, std::sync::atomic::Ordering::AcqRel);
}
}
#[doc(hidden)]
pub struct Iter<T>(PriorityQueueReceiver<T>);
impl<T> Iterator for Iter<T> {
type Item = T;
fn next(&mut self) -> Option<Self::Item> {
self.0.pop().ok()
}
}
impl<T> FusedIterator for Iter<T> {}
#[doc(hidden)]
pub struct TryIter<T> {
receiver: PriorityQueueReceiver<T>,
ended: bool,
}
impl<T> Iterator for TryIter<T> {
type Item = Result<T, RecvError>;
fn next(&mut self) -> Option<Self::Item> {
if self.ended {
return None;
}
let res = self.receiver.try_pop();
self.ended = res.is_err();
res.transpose()
}
}
impl<T> FusedIterator for TryIter<T> {}
#[cfg(test)]
mod tests {
use crate::collections::HashSet;
use super::*;
#[test]
fn all_tasks_get_yielded() {
let (tx, mut rx) = PriorityQueueReceiver::new();
tx.send(Priority::Medium, 20).unwrap();
tx.send(Priority::High, 30).unwrap();
tx.send(Priority::Low, 10).unwrap();
tx.send(Priority::Medium, 21).unwrap();
tx.send(Priority::High, 31).unwrap();
drop(tx);
assert_eq!(
rx.iter().collect::<HashSet<_>>(),
[30, 31, 20, 21, 10].into_iter().collect::<HashSet<_>>()
)
}
#[test]
fn new_high_prio_task_get_scheduled_quickly() {
let (tx, mut rx) = PriorityQueueReceiver::new();
for _ in 0..100 {
tx.send(Priority::Low, 1).unwrap();
}
assert_eq!(rx.pop().unwrap(), 1);
tx.send(Priority::High, 3).unwrap();
assert_eq!(rx.pop().unwrap(), 3);
assert_eq!(rx.pop().unwrap(), 1);
}
}