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use crate::loom::sync::atomic::AtomicBool;
use std::cell::UnsafeCell;
use std::marker::PhantomData;
use std::ops::{Deref, DerefMut};
use std::sync::atomic::Ordering::SeqCst;
pub(crate) struct TryLock<T> {
locked: AtomicBool,
data: UnsafeCell<T>,
}
pub(crate) struct LockGuard<'a, T> {
lock: &'a TryLock<T>,
_p: PhantomData<std::rc::Rc<()>>,
}
unsafe impl<T: Send> Send for TryLock<T> {}
unsafe impl<T: Send> Sync for TryLock<T> {}
unsafe impl<T: Sync> Sync for LockGuard<'_, T> {}
macro_rules! new {
($data:ident) => {
TryLock {
locked: AtomicBool::new(false),
data: UnsafeCell::new($data),
}
};
}
impl<T> TryLock<T> {
#[cfg(not(loom))]
/// Create a new `TryLock`
pub(crate) const fn new(data: T) -> TryLock<T> {
new!(data)
}
#[cfg(loom)]
/// Create a new `TryLock`
pub(crate) fn new(data: T) -> TryLock<T> {
new!(data)
}
/// Attempt to acquire lock
pub(crate) fn try_lock(&self) -> Option<LockGuard<'_, T>> {
if self
.locked
.compare_exchange(false, true, SeqCst, SeqCst)
.is_err()
{
return None;
}
Some(LockGuard {
lock: self,
_p: PhantomData,
})
}
}
impl<T> Deref for LockGuard<'_, T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { &*self.lock.data.get() }
}
}
impl<T> DerefMut for LockGuard<'_, T> {
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut *self.lock.data.get() }
}
}
impl<T> Drop for LockGuard<'_, T> {
fn drop(&mut self) {
self.lock.locked.store(false, SeqCst);
}
}