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use crate::sys::pal::waitqueue::{SpinMutex, WaitQueue, WaitVariable, try_lock_or_false};
use crate::sys::sync::OnceBox;
pub struct Mutex {
// FIXME: `UnsafeList` is not movable.
inner: OnceBox<SpinMutex<WaitVariable<bool>>>,
}
// Implementation according to “Operating Systems: Three Easy Pieces”, chapter 28
impl Mutex {
pub const fn new() -> Mutex {
Mutex { inner: OnceBox::new() }
}
fn get(&self) -> &SpinMutex<WaitVariable<bool>> {
self.inner.get_or_init(|| Box::pin(SpinMutex::new(WaitVariable::new(false)))).get_ref()
}
#[inline]
pub fn lock(&self) {
let mut guard = self.get().lock();
if *guard.lock_var() {
// Another thread has the lock, wait
WaitQueue::wait(guard, || {})
// Another thread has passed the lock to us
} else {
// We are just now obtaining the lock
*guard.lock_var_mut() = true;
}
}
#[inline]
pub unsafe fn unlock(&self) {
// SAFETY: the mutex was locked by the current thread, so it has been
// initialized already.
let guard = unsafe { self.inner.get_unchecked().get_ref().lock() };
if let Err(mut guard) = WaitQueue::notify_one(guard) {
// No other waiters, unlock
*guard.lock_var_mut() = false;
} else {
// There was a thread waiting, just pass the lock
}
}
#[inline]
pub fn try_lock(&self) -> bool {
let mut guard = try_lock_or_false!(self.get());
if *guard.lock_var() {
// Another thread has the lock
false
} else {
// We are just now obtaining the lock
*guard.lock_var_mut() = true;
true
}
}
}
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