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use core::cell::Cell;
use critical_section::{CriticalSection, Mutex};
pub(crate) use critical_section::{CriticalSection as Token, with as locked};
#[cfg(target_arch = "avr")]
type StateBits = u8;
#[cfg(not(target_arch = "avr"))]
type StateBits = usize;
/// Task is spawned (has a future)
pub(crate) const STATE_SPAWNED: StateBits = 1 << 0;
/// Task is in the executor run queue
pub(crate) const STATE_RUN_QUEUED: StateBits = 1 << 1;
pub(crate) struct State {
state: Mutex<Cell<StateBits>>,
}
impl State {
pub const fn new() -> State {
Self {
state: Mutex::new(Cell::new(0)),
}
}
fn update<R>(&self, f: impl FnOnce(&mut StateBits) -> R) -> R {
critical_section::with(|cs| self.update_with_cs(cs, f))
}
fn update_with_cs<R>(&self, cs: CriticalSection<'_>, f: impl FnOnce(&mut StateBits) -> R) -> R {
let s = self.state.borrow(cs);
let mut val = s.get();
let r = f(&mut val);
s.set(val);
r
}
/// If task is idle, mark it as spawned + run_queued and return true.
#[inline(always)]
pub fn spawn(&self) -> bool {
self.update(|s| {
if *s == 0 {
*s = STATE_SPAWNED | STATE_RUN_QUEUED;
true
} else {
false
}
})
}
/// Unmark the task as spawned.
#[inline(always)]
pub fn despawn(&self) {
self.update(|s| *s &= !STATE_SPAWNED);
}
/// 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)) {
critical_section::with(|cs| {
if self.update_with_cs(cs, |s| {
let ok = *s & STATE_RUN_QUEUED == 0;
*s |= STATE_RUN_QUEUED;
ok
}) {
f(cs);
}
});
}
/// Unmark the task as run-queued. Return whether the task is spawned.
#[inline(always)]
pub fn run_dequeue(&self, cs: CriticalSection<'_>) {
self.update_with_cs(cs, |s| *s &= !STATE_RUN_QUEUED)
}
}
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