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Remove `RwLock.downgrade` due to potential contention with `RwLock.read`

This commit is contained in:
Ruize Tang 2025-05-24 22:28:39 +08:00 committed by Tate, Hongliang Tian
parent d75a2481bb
commit 50eaffc731
1 changed files with 0 additions and 33 deletions
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33
ostd/src/sync/rwlock.rs
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@ -463,39 +463,6 @@ impl<T: ?Sized, R: Deref<Target = RwLock<T, G>> + Clone, G: SpinGuardian> Deref
}
}
impl<T: ?Sized, R: Deref<Target = RwLock<T, G>> + Clone, G: SpinGuardian>
RwLockWriteGuard_<T, R, G>
{
/// Atomically downgrades a write guard to an upgradeable reader guard.
///
/// This method always succeeds because the lock is exclusively held by the writer.
pub fn downgrade(mut self) -> RwLockUpgradeableGuard_<T, R, G> {
loop {
self = match self.try_downgrade() {
Ok(guard) => return guard,
Err(e) => e,
};
}
}
/// This is not exposed as a public method to prevent intermediate lock states from affecting the
/// downgrade process.
fn try_downgrade(mut self) -> Result<RwLockUpgradeableGuard_<T, R, G>, Self> {
let inner = self.inner.clone();
let res = self
.inner
.lock
.compare_exchange(WRITER, UPGRADEABLE_READER, AcqRel, Relaxed);
if res.is_ok() {
let guard = self.guard.transfer_to();
drop(self);
Ok(RwLockUpgradeableGuard_ { inner, guard })
} else {
Err(self)
}
}
}
impl<T: ?Sized, R: Deref<Target = RwLock<T, G>> + Clone, G: SpinGuardian> DerefMut
for RwLockWriteGuard_<T, R, G>
{