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Re-introduce a way to get the allocation size of a table #553

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Sep 18, 2024
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19 changes: 19 additions & 0 deletions src/map.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1929,6 +1929,16 @@ where
let hash = make_hash::<Q, S>(&self.hash_builder, k);
self.table.remove_entry(hash, equivalent_key(k))
}

/// Returns the total amount of memory allocated internally by the hash
/// set, in bytes.
///
/// The returned number is informational only. It is intended to be
/// primarily used for memory profiling.
#[inline]
pub fn allocation_size(&self) -> usize {
self.table.allocation_size()
}
}

impl<K, V, S, A> PartialEq for HashMap<K, V, S, A>
Expand Down Expand Up @@ -6416,4 +6426,13 @@ mod test_map {
// All allocator clones should already be dropped.
assert_eq!(dropped.load(Ordering::SeqCst), 0);
}

#[test]
fn test_allocation_info() {
assert_eq!(HashMap::<(), ()>::new().allocation_size(), 0);
assert_eq!(HashMap::<u32, u32>::new().allocation_size(), 0);
assert!(
HashMap::<u32, u32>::with_capacity(1).allocation_size() > core::mem::size_of::<u32>()
);
}
}
39 changes: 39 additions & 0 deletions src/raw/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -771,6 +771,18 @@ impl<T, A: Allocator> RawTable<T, A> {
NonNull::new_unchecked(self.data_end().as_ptr().wrapping_sub(self.buckets()))
}

/// Returns the total amount of memory allocated internally by the hash
/// table, in bytes.
///
/// The returned number is informational only. It is intended to be
/// primarily used for memory profiling.
#[inline]
pub fn allocation_size(&self) -> usize {
// SAFETY: We use the same `table_layout` that was used to allocate
// this table.
unsafe { self.table.allocation_size_or_zero(Self::TABLE_LAYOUT) }
}

/// Returns the index of a bucket from a `Bucket`.
#[inline]
pub unsafe fn bucket_index(&self, bucket: &Bucket<T>) -> usize {
Expand Down Expand Up @@ -3056,6 +3068,33 @@ impl RawTableInner {
)
}

/// Returns the total amount of memory allocated internally by the hash
/// table, in bytes.
///
/// The returned number is informational only. It is intended to be
/// primarily used for memory profiling.
///
/// # Safety
///
/// The `table_layout` must be the same [`TableLayout`] as the `TableLayout`
/// that was used to allocate this table. Failure to comply with this condition
/// may result in [`undefined behavior`].
///
///
/// [`undefined behavior`]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
#[inline]
unsafe fn allocation_size_or_zero(&self, table_layout: TableLayout) -> usize {
if self.is_empty_singleton() {
0
} else {
// SAFETY:
// 1. We have checked that our table is allocated.
// 2. The caller ensures that `table_layout` matches the [`TableLayout`]
// that was used to allocate this table.
unsafe { self.allocation_info(table_layout).1.size() }
}
}

/// Marks all table buckets as empty without dropping their contents.
#[inline]
fn clear_no_drop(&mut self) {
Expand Down
17 changes: 17 additions & 0 deletions src/set.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1230,6 +1230,16 @@ where
None => None,
}
}

/// Returns the total amount of memory allocated internally by the hash
/// set, in bytes.
///
/// The returned number is informational only. It is intended to be
/// primarily used for memory profiling.
#[inline]
pub fn allocation_size(&self) -> usize {
self.map.allocation_size()
}
}

impl<T, S, A> PartialEq for HashSet<T, S, A>
Expand Down Expand Up @@ -3055,4 +3065,11 @@ mod test_set {
// (and without the `map`, it does not).
let mut _set: HashSet<_> = (0..3).map(|_| ()).collect();
}

#[test]
fn test_allocation_info() {
assert_eq!(HashSet::<()>::new().allocation_size(), 0);
assert_eq!(HashSet::<u32>::new().allocation_size(), 0);
assert!(HashSet::<u32>::with_capacity(1).allocation_size() > core::mem::size_of::<u32>());
}
}
22 changes: 22 additions & 0 deletions src/table.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1088,6 +1088,16 @@ where
) -> Option<[&'_ mut T; N]> {
self.raw.get_many_unchecked_mut(hashes, eq)
}

/// Returns the total amount of memory allocated internally by the hash
/// table, in bytes.
///
/// The returned number is informational only. It is intended to be
/// primarily used for memory profiling.
#[inline]
pub fn allocation_size(&self) -> usize {
self.raw.allocation_size()
}
}

impl<T, A> IntoIterator for HashTable<T, A>
Expand Down Expand Up @@ -2208,3 +2218,15 @@ where
}

impl<T, F, A: Allocator> FusedIterator for ExtractIf<'_, T, F, A> where F: FnMut(&mut T) -> bool {}

#[cfg(test)]
mod tests {
use super::HashTable;

#[test]
fn test_allocation_info() {
assert_eq!(HashTable::<()>::new().allocation_size(), 0);
assert_eq!(HashTable::<u32>::new().allocation_size(), 0);
assert!(HashTable::<u32>::with_capacity(1).allocation_size() > core::mem::size_of::<u32>());
}
}
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