zc706/libcortex_a9/src/semaphore.rs

72 lines
1.8 KiB
Rust

use super::{spin_lock_yield, notify_spin_lock};
use core::{
task::{Context, Poll},
pin::Pin,
future::Future,
sync::atomic::{AtomicI32, Ordering}
};
pub struct Semaphore {
value: AtomicI32,
max: i32
}
impl Semaphore {
pub const fn new(value: i32, max: i32) -> Self {
Semaphore { value: AtomicI32::new(value), max}
}
pub fn try_wait(&self) -> Option<()> {
loop {
let value = self.value.load(Ordering::Relaxed);
if value > 0 {
if self.value.compare_exchange_weak(value, value - 1, Ordering::SeqCst, Ordering::Relaxed).is_ok() {
return Some(());
}
} else {
return None;
}
}
}
pub fn wait(&self) {
while self.try_wait().is_none() {
spin_lock_yield();
}
}
pub async fn async_wait(&self) {
struct Fut<'a>(&'a Semaphore);
impl Future for Fut<'_> {
type Output = ();
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
match self.0.try_wait() {
Some(_) => Poll::Ready(()),
None => {
cx.waker().wake_by_ref();
Poll::Pending
}
}
}
}
Fut(&self).await
}
pub fn signal(&self) {
loop {
let value = self.value.load(Ordering::Relaxed);
if value < self.max {
if self.value.compare_exchange_weak(value, value + 1, Ordering::SeqCst, Ordering::Relaxed).is_ok() {
notify_spin_lock();
return;
}
} else {
return;
}
}
}
}