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Switch from 'Option' to 'ManuallyDrop' for blocking guard's inner #1176

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Switch from 'Option' to 'ManuallyDrop' for blocking guard's inner #1176

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23 changes: 14 additions & 9 deletions godot-cell/src/blocking_guards.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
* file, You can obtain one at https://mozilla.org/MPL/2.0/.
*/

use std::mem::ManuallyDrop;
use std::ops::{Deref, DerefMut};
use std::sync::{Arc, Condvar, Mutex};

Expand All @@ -16,7 +17,7 @@ use crate::guards::{MutGuard, RefGuard};
/// See [`panicking::RefGuard`](crate::panicking::RefGuard) for more details.
#[derive(Debug)]
pub struct RefGuardBlocking<'a, T> {
inner: Option<RefGuard<'a, T>>,
inner: ManuallyDrop<RefGuard<'a, T>>,
mut_condition: Arc<Condvar>,
state: Arc<Mutex<ThreadTracker>>,
}
Expand All @@ -28,7 +29,7 @@ impl<'a, T> RefGuardBlocking<'a, T> {
state: Arc<Mutex<ThreadTracker>>,
) -> Self {
Self {
inner: Some(inner),
inner: ManuallyDrop::new(inner),
mut_condition,
state,
}
Expand All @@ -39,7 +40,7 @@ impl<'a, T> Deref for RefGuardBlocking<'a, T> {
type Target = <RefGuard<'a, T> as Deref>::Target;

fn deref(&self) -> &Self::Target {
self.inner.as_ref().unwrap().deref()
self.inner.deref().deref()
}
}

Expand All @@ -49,7 +50,9 @@ impl<T> Drop for RefGuardBlocking<'_, T> {

state_lock.decrement_current_thread_shared_count();

drop(self.inner.take());
unsafe {
ManuallyDrop::drop(&mut self.inner);
}
Comment on lines +53 to +55
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Also here.


self.mut_condition.notify_one();
drop(state_lock);
Expand All @@ -61,7 +64,7 @@ impl<T> Drop for RefGuardBlocking<'_, T> {
/// See [`panicking::MutGuard`](crate::panicking::MutGuard) for more details.
#[derive(Debug)]
pub struct MutGuardBlocking<'a, T> {
inner: Option<MutGuard<'a, T>>,
inner: ManuallyDrop<MutGuard<'a, T>>,
mut_condition: Arc<Condvar>,
immut_condition: Arc<Condvar>,
}
Expand All @@ -73,7 +76,7 @@ impl<'a, T> MutGuardBlocking<'a, T> {
immut_condition: Arc<Condvar>,
) -> Self {
Self {
inner: Some(inner),
inner: ManuallyDrop::new(inner),
immut_condition,
mut_condition,
}
Expand All @@ -84,19 +87,21 @@ impl<'a, T> Deref for MutGuardBlocking<'a, T> {
type Target = <MutGuard<'a, T> as Deref>::Target;

fn deref(&self) -> &Self::Target {
self.inner.as_ref().unwrap().deref()
self.inner.deref().deref()
}
}

impl<T> DerefMut for MutGuardBlocking<'_, T> {
fn deref_mut(&mut self) -> &mut Self::Target {
self.inner.as_mut().unwrap().deref_mut()
self.inner.deref_mut().deref_mut()
}
}

impl<T> Drop for MutGuardBlocking<'_, T> {
fn drop(&mut self) {
drop(self.inner.take());
unsafe {
ManuallyDrop::drop(&mut self.inner);
}
Comment on lines +102 to +104
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Please add a safety statement:

Suggested change
unsafe {
ManuallyDrop::drop(&mut self.inner);
}
// SAFETY: guard is dropped exactly once, here.
unsafe {
ManuallyDrop::drop(&mut self.inner);
}


self.mut_condition.notify_one();
self.immut_condition.notify_all();
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