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improve performance of recursion guard #1156

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merged 7 commits into from Jan 15, 2024
Merged

improve performance of recursion guard #1156

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f98b085
improve performance of recursion guard
samuelcolvin Jan 14, 2024
5d14e70
tweak depth limit logic
samuelcolvin Jan 14, 2024
3e73e52
bump
samuelcolvin Jan 14, 2024
3a621b7
bump
samuelcolvin Jan 15, 2024
3f72522
tidy up `contains_or_insert` to be more efficient
davidhewitt Jan 15, 2024
e1190ed
remove cargo.toml release profile change
samuelcolvin Jan 15, 2024
4b82950
codify the stack-based nature of the guard
davidhewitt Jan 15, 2024
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28 changes: 13 additions & 15 deletions src/recursion_guard.rs
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Expand Up @@ -95,29 +95,26 @@ impl<T: Eq + Hash + Clone> SmallContainer<T> {
pub fn contains_or_insert(&mut self, v: T) -> Option<usize> {
match self {
Self::Array(array) => {
let mut first_slot: Option<usize> = None;
for (index, op_value) in array.iter().enumerate() {
for (index, op_value) in array.iter_mut().enumerate() {
if let Some(existing) = op_value {
if existing == &v {
return None;
}
} else {
first_slot = first_slot.or(Some(index));
*op_value = Some(v);
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i don't think this is safe because there's a case where an earlier item has been removed from the array, but later values are still set.

E.g.

array = [123, 456, None, 789]

If you're looking up 789 it wouldn't be found in this case.

I had this before, but changed it to be safer.

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I guess if we can be sure that new items are always added to the array (and removed) inside parent calls, we can be sure that there will never be None caps in the array.

@davidhewitt if you're confident of that, we can go ahead with this change. Worst case we just fallback on the depth guard.

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Pushed another commit which should work more like a stack, and we'll panic if the code is wrong.

return Some(index);
}
}
if let Some(index) = first_slot {
array[index] = Some(v);
first_slot
} else {
let mut set: AHashSet<T> = AHashSet::with_capacity(ARRAY_SIZE + 1);
for existing in array.iter_mut() {
set.insert(existing.take().unwrap());
}
set.insert(v);
*self = Self::Set(set);
// id doesn't matter here as we'll be removing from a set
Some(0)

// No array slots exist; convert to set
let mut set: AHashSet<T> = AHashSet::with_capacity(ARRAY_SIZE + 1);
for existing in array.iter_mut() {
set.insert(existing.take().unwrap());
}
set.insert(v);
*self = Self::Set(set);
// id doesn't matter here as we'll be removing from a set
Some(0)
}
// https://doc.rust-lang.org/std/collections/struct.HashSet.html#method.insert
// "If the set did not have this value present, `true` is returned."
Expand All @@ -135,6 +132,7 @@ impl<T: Eq + Hash + Clone> SmallContainer<T> {
pub fn remove(&mut self, v: &T, index: usize) {
match self {
Self::Array(array) => {
debug_assert!(array[index].as_ref() == Some(v), "remove did not match insert");
array[index] = None;
}
Self::Set(set) => {
Expand Down