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//! Trivial spinlock-based implementation of `sync::Mutex`.
// FIXME: Perhaps use Intel TSX to avoid locking?
#[cfg(test)]
mod tests;
use crate::cell::UnsafeCell;
use crate::hint;
use crate::ops::{Deref, DerefMut};
use crate::sync::atomic::{AtomicBool, Ordering};
#[derive(Default)]
pub struct SpinMutex<T> {
value: UnsafeCell<T>,
lock: AtomicBool,
}
unsafe impl<T: Send> Send for SpinMutex<T> {}
unsafe impl<T: Send> Sync for SpinMutex<T> {}
pub struct SpinMutexGuard<'a, T: 'a> {
mutex: &'a SpinMutex<T>,
}
impl<'a, T> !Send for SpinMutexGuard<'a, T> {}
unsafe impl<'a, T: Sync> Sync for SpinMutexGuard<'a, T> {}
impl<T> SpinMutex<T> {
pub const fn new(value: T) -> Self {
SpinMutex { value: UnsafeCell::new(value), lock: AtomicBool::new(false) }
}
#[inline(always)]
pub fn lock(&self) -> SpinMutexGuard<'_, T> {
loop {
match self.try_lock() {
None => {
while self.lock.load(Ordering::Relaxed) {
hint::spin_loop()
}
}
Some(guard) => return guard,
}
}
}
#[inline(always)]
pub fn try_lock(&self) -> Option<SpinMutexGuard<'_, T>> {
if self.lock.compare_exchange(false, true, Ordering::Acquire, Ordering::Acquire).is_ok() {
Some(SpinMutexGuard { mutex: self })
} else {
None
}
}
}
/// Lock the Mutex or return false.
pub macro try_lock_or_false($e:expr) {
if let Some(v) = $e.try_lock() { v } else { return false }
}
impl<'a, T> Deref for SpinMutexGuard<'a, T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { &*self.mutex.value.get() }
}
}
impl<'a, T> DerefMut for SpinMutexGuard<'a, T> {
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut *self.mutex.value.get() }
}
}
impl<'a, T> Drop for SpinMutexGuard<'a, T> {
fn drop(&mut self) {
self.mutex.lock.store(false, Ordering::Release)
}
}
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