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use core::sync::atomic::{AtomicU8, Ordering};
#[derive(Clone, Copy)]
pub(crate) struct Token(());
/// Creates a token and passes it to the closure.
///
/// This is a no-op replacement for `CriticalSection::with` because we don't need any locking.
pub(crate) fn locked<R>(f: impl FnOnce(Token) -> R) -> R {
f(Token(()))
}
/// Task is spawned (has a future)
pub(crate) const STATE_SPAWNED: u8 = 1 << 0;
/// Task is in the executor run queue
pub(crate) const STATE_RUN_QUEUED: u8 = 1 << 1;
pub(crate) struct State {
state: AtomicU8,
}
impl State {
pub const fn new() -> State {
Self {
state: AtomicU8::new(0),
}
}
/// If task is idle, mark it as spawned + run_queued and return true.
#[inline(always)]
pub fn spawn(&self) -> bool {
self.state
.compare_exchange(0, STATE_SPAWNED | STATE_RUN_QUEUED, Ordering::AcqRel, Ordering::Acquire)
.is_ok()
}
/// Unmark the task as spawned.
#[inline(always)]
pub fn despawn(&self) {
self.state.fetch_and(!STATE_SPAWNED, Ordering::AcqRel);
}
/// Mark the task as run-queued if it's spawned and isn't already run-queued. Run the given
/// function if the task was successfully marked.
#[inline(always)]
pub fn run_enqueue(&self, f: impl FnOnce(Token)) {
let prev = self.state.fetch_or(STATE_RUN_QUEUED, Ordering::AcqRel);
if prev & STATE_RUN_QUEUED == 0 {
locked(f);
}
}
/// Unmark the task as run-queued. Return whether the task is spawned.
#[inline(always)]
pub fn run_dequeue(&self) {
self.state.fetch_and(!STATE_RUN_QUEUED, Ordering::AcqRel);
}
}
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