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Relax atomic loads and stores in Table #766

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Relax atomic loads and stores in Table #766

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18 changes: 13 additions & 5 deletions src/table.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -289,13 +289,13 @@ impl Table {

impl<'p, T: Slot> PageView<'p, T> {
fn page_data(&self) -> &[PageDataEntry<T>] {
let len = self.0.allocated.load(Ordering::Acquire);
let len = self.0.allocated();
// SAFETY: `len` is the initialized length of the page
unsafe { slice::from_raw_parts(self.0.data.cast::<PageDataEntry<T>>().as_ptr(), len) }
}

fn data(&self) -> &'p [T] {
let len = self.0.allocated.load(Ordering::Acquire);
let len = self.0.allocated();
// SAFETY: `len` is the initialized length of the page
unsafe { slice::from_raw_parts(self.0.data.cast::<T>().as_ptr(), len) }
}
Expand All @@ -305,7 +305,7 @@ impl<'p, T: Slot> PageView<'p, T> {
V: FnOnce(Id) -> T,
{
let _guard = self.0.allocation_lock.lock();
let index = self.0.allocated.load(Ordering::Acquire);
let index = self.0.allocated();
if index >= PAGE_LEN {
return Err(value);
}
Expand All @@ -320,7 +320,8 @@ impl<'p, T: Slot> PageView<'p, T> {

// Update the length (this must be done after initialization as otherwise an uninitialized
// read could occur!)
self.0.allocated.store(index + 1, Ordering::Release);
// Ordering: Relaxed is fine as the `allocation_lock` establishes a happens-before relationship
self.0.allocated.store(index + 1, Ordering::Relaxed);

Ok(id)
}
Expand All @@ -341,13 +342,20 @@ impl Page {
}
}

#[inline]
fn allocated(&self) -> usize {
// Ordering: Relaxed is fine as the `allocation_lock` establishes a happens-before
// relationship
self.allocated.load(Ordering::Relaxed)
}

/// Retrieves the pointer for the given slot.
///
/// # Panics
///
/// If slot is out of bounds
fn get(&self, slot: SlotIndex) -> *mut () {
let len = self.allocated.load(Ordering::Acquire);
let len = self.allocated();
assert!(
slot.0 < len,
"out of bounds access `{slot:?}` (maximum slot `{len}`)"
Expand Down