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Change finish_shrink to remap entries in shrunk space

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This commit is contained in:
David Freifeld
2025-06-23 16:15:43 -07:00
parent 610ea22c46
commit 93a45708ff
2 changed files with 32 additions and 28 deletions
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51
libs/neon-shmem/src/hash.rs
View File

@@ -282,7 +282,7 @@ where
inner.buckets = buckets; inner.buckets = buckets;
} }
/// Rehash the map. Intended for benchmarking only. /// Rehash the map. Intended for benchmarking only.
pub fn shuffle(&mut self) { pub fn shuffle(&mut self) {
let map = unsafe { self.shared_ptr.as_mut() }.unwrap(); let map = unsafe { self.shared_ptr.as_mut() }.unwrap();
let inner = &mut map.inner; let inner = &mut map.inner;
@@ -352,7 +352,7 @@ where
Ok(()) Ok(())
} }
/// Begin a shrink, limiting all new allocations to be in buckets with index less than `num_buckets`. /// Begin a shrink, limiting all new allocations to be in buckets with index less than `num_buckets`.
pub fn begin_shrink(&mut self, num_buckets: u32) { pub fn begin_shrink(&mut self, num_buckets: u32) {
let map = unsafe { self.shared_ptr.as_mut() }.unwrap(); let map = unsafe { self.shared_ptr.as_mut() }.unwrap();
if num_buckets > map.inner.get_num_buckets() as u32 { if num_buckets > map.inner.get_num_buckets() as u32 {
@@ -377,32 +377,28 @@ where
if inner.get_num_buckets() == num_buckets as usize { if inner.get_num_buckets() == num_buckets as usize {
return Ok(()); return Ok(());
} } else if inner.get_num_buckets() > num_buckets as usize {
panic!("called finish_shrink before enough entries were removed");
}
for i in (num_buckets as usize)..inner.buckets.len() { for i in (num_buckets as usize)..inner.buckets.len() {
if inner.buckets[i].inner.is_some() { if let Some((k, v)) = inner.buckets[i].inner.take() {
// TODO(quantumish) Do we want to treat this as a violation of an invariant inner.alloc_bucket(k, v, inner.buckets[i].prev.unwrap_first()).unwrap();
// or a legitimate error the caller can run into? Originally I thought this } else {
// could return something like a UnevictedError(index) as soon as it runs match inner.buckets[i].prev {
// into something (that way a caller could clear their soon-to-be-shrinked PrevPos::First(_) => {
// buckets by repeatedly trying to call `finish_shrink`). let next_pos = inner.buckets[i].next;
// inner.free_head = next_pos;
// Would require making a wider error type enum with this and shmem errors. if next_pos != INVALID_POS {
panic!("unevicted entries in shrinked space") inner.buckets[next_pos as usize].prev = PrevPos::First(INVALID_POS);
} }
match inner.buckets[i].prev { },
PrevPos::First(_) => { PrevPos::Chained(j) => {
let next_pos = inner.buckets[i].next; let next_pos = inner.buckets[i].next;
inner.free_head = next_pos; inner.buckets[j as usize].next = next_pos;
if next_pos != INVALID_POS { if next_pos != INVALID_POS {
inner.buckets[next_pos as usize].prev = PrevPos::First(INVALID_POS); inner.buckets[next_pos as usize].prev = PrevPos::Chained(j);
} }
},
PrevPos::Chained(j) => {
let next_pos = inner.buckets[i].next;
inner.buckets[j as usize].next = next_pos;
if next_pos != INVALID_POS {
inner.buckets[next_pos as usize].prev = PrevPos::Chained(j);
} }
} }
} }
@@ -421,6 +417,5 @@ where
inner.alloc_limit = INVALID_POS; inner.alloc_limit = INVALID_POS;
Ok(()) Ok(())
} }
} }

9
libs/neon-shmem/src/hash/entry.rs
View File

@@ -16,6 +16,15 @@ pub(crate) enum PrevPos {
Chained(u32), Chained(u32),
} }
impl PrevPos {
pub fn unwrap_first(&self) -> u32 {
match self {
Self::First(i) => *i,
_ => panic!("not first entry in chain")
}
}
}
pub struct OccupiedEntry<'a, 'b, K, V> { pub struct OccupiedEntry<'a, 'b, K, V> {
pub(crate) map: &'b mut CoreHashMap<'a, K, V>, pub(crate) map: &'b mut CoreHashMap<'a, K, V>,
pub(crate) _key: K, // The key of the occupied entry pub(crate) _key: K, // The key of the occupied entry