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use core::cell::Cell;
use core::cmp::min;
use core::ptr;
use core::ptr::NonNull;
use atomic_polyfill::Ordering;
use super::{TaskHeader, STATE_TIMER_QUEUED};
use crate::time::Instant;
pub(crate) struct TimerQueueItem {
next: Cell<*mut TaskHeader>,
}
impl TimerQueueItem {
pub const fn new() -> Self {
Self {
next: Cell::new(ptr::null_mut()),
}
}
}
pub(crate) struct TimerQueue {
head: Cell<*mut TaskHeader>,
}
impl TimerQueue {
pub const fn new() -> Self {
Self {
head: Cell::new(ptr::null_mut()),
}
}
pub(crate) unsafe fn update(&self, p: NonNull<TaskHeader>) {
let task = p.as_ref();
if task.expires_at.get() != Instant::MAX {
let old_state = task.state.fetch_or(STATE_TIMER_QUEUED, Ordering::AcqRel);
let is_new = old_state & STATE_TIMER_QUEUED == 0;
if is_new {
task.timer_queue_item.next.set(self.head.get());
self.head.set(p.as_ptr());
}
}
}
pub(crate) unsafe fn next_expiration(&self) -> Instant {
let mut res = Instant::MAX;
self.retain(|p| {
let task = p.as_ref();
let expires = task.expires_at.get();
res = min(res, expires);
expires != Instant::MAX
});
res
}
pub(crate) unsafe fn dequeue_expired(&self, now: Instant, on_task: impl Fn(NonNull<TaskHeader>)) {
self.retain(|p| {
let task = p.as_ref();
if task.expires_at.get() <= now {
on_task(p);
false
} else {
true
}
});
}
pub(crate) unsafe fn retain(&self, mut f: impl FnMut(NonNull<TaskHeader>) -> bool) {
let mut prev = &self.head;
while !prev.get().is_null() {
let p = NonNull::new_unchecked(prev.get());
let task = &*p.as_ptr();
if f(p) {
// Skip to next
prev = &task.timer_queue_item.next;
} else {
// Remove it
prev.set(task.timer_queue_item.next.get());
task.state.fetch_and(!STATE_TIMER_QUEUED, Ordering::AcqRel);
}
}
}
}
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