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revset: refactor collect_dag_range() and walk_*() helpers #2688

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merged 4 commits into from
Dec 11, 2023
Merged

revset: refactor collect_dag_range() and walk_*() helpers #2688

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025b6b2
index: reimplement collect_dag_range() of revset engine as iterator
yuja Apr 22, 2023
221a500
revset: inline collect_dag_range()
yuja Apr 22, 2023
c2c0c09
revset: inline walk_children()
yuja May 28, 2023
d0e483b
revset: inline walk_ancestors()
yuja May 28, 2023
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53 changes: 53 additions & 0 deletions lib/src/default_index_store.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ use std::fmt::{Debug, Formatter};
use std::fs::File;
use std::hash::{Hash, Hasher};
use std::io::{Read, Write};
use std::iter::FusedIterator;
use std::ops::Range;
use std::path::{Path, PathBuf};
use std::sync::Arc;
Expand Down Expand Up @@ -1381,6 +1382,18 @@ impl<'a> RevWalk<'a> {
self.take_while(move |entry| entry.position() >= bottom_position)
}

/// Fully consumes the ancestors and walks back from `root_positions`.
///
/// The returned iterator yields entries in order of ascending index
/// position.
pub fn descendants(self, root_positions: &[IndexPosition]) -> RevWalkDescendants<'a> {
RevWalkDescendants {
candidate_entries: self.take_until_roots(root_positions).collect(),
root_positions: root_positions.iter().copied().collect(),
reachable_positions: HashSet::new(),
}
}

/// Fully consumes the ancestors and walks back from `root_positions` within
/// `generation_range`.
///
Expand Down Expand Up @@ -1589,6 +1602,46 @@ impl RevWalkItemGenerationRange {
}
}

/// Walks descendants from the roots, in order of ascending index position.
#[derive(Clone)]
pub struct RevWalkDescendants<'a> {
candidate_entries: Vec<IndexEntry<'a>>,
root_positions: HashSet<IndexPosition>,
reachable_positions: HashSet<IndexPosition>,
}

impl RevWalkDescendants<'_> {
/// Builds a set of index positions reachable from the roots.
///
/// This is equivalent to `.map(|entry| entry.position()).collect()` on
/// the new iterator, but returns the internal buffer instead.
pub fn collect_positions_set(mut self) -> HashSet<IndexPosition> {
self.by_ref().for_each(drop);
self.reachable_positions
}
}

impl<'a> Iterator for RevWalkDescendants<'a> {
type Item = IndexEntry<'a>;

fn next(&mut self) -> Option<Self::Item> {
while let Some(candidate) = self.candidate_entries.pop() {
if self.root_positions.contains(&candidate.position())
|| candidate
.parent_positions()
.iter()
.any(|parent_pos| self.reachable_positions.contains(parent_pos))
{
self.reachable_positions.insert(candidate.position());
return Some(candidate);
}
}
None
}
}

impl FusedIterator for RevWalkDescendants<'_> {}

/// Removes the greatest items (including duplicates) from the heap, returns
/// one.
fn dedup_pop<T: Ord>(heap: &mut BinaryHeap<T>) -> Option<T> {
Expand Down
131 changes: 44 additions & 87 deletions lib/src/default_revset_engine.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,9 +24,7 @@ use std::sync::Arc;
use itertools::Itertools;

use crate::backend::{ChangeId, CommitId, MillisSinceEpoch};
use crate::default_index_store::{
CompositeIndex, IndexEntry, IndexEntryByPosition, IndexPosition, RevWalk,
};
use crate::default_index_store::{CompositeIndex, IndexEntry, IndexEntryByPosition, IndexPosition};
use crate::default_revset_graph_iterator::RevsetGraphIterator;
use crate::id_prefix::{IdIndex, IdIndexSource, IdIndexSourceEntry};
use crate::index::{HexPrefix, PrefixResolution};
Expand Down Expand Up @@ -538,7 +536,8 @@ impl<'index> EvaluationContext<'index> {
}
ResolvedExpression::Ancestors { heads, generation } => {
let head_set = self.evaluate(heads)?;
let walk = self.walk_ancestors(&*head_set);
let head_positions = head_set.iter().map(|entry| entry.position()).collect_vec();
let walk = self.index.walk_revs(&head_positions, &[]);
if generation == &GENERATION_RANGE_FULL {
Ok(Box::new(RevWalkRevset { walk }))
} else {
Expand Down Expand Up @@ -568,26 +567,47 @@ impl<'index> EvaluationContext<'index> {
heads,
generation_from_roots,
} => {
let index = self.index;
let root_set = self.evaluate(roots)?;
let root_positions = root_set.iter().map(|entry| entry.position()).collect_vec();
let head_set = self.evaluate(heads)?;
let head_positions = head_set.iter().map(|entry| entry.position()).collect_vec();
if generation_from_roots == &(1..2) {
Ok(Box::new(self.walk_children(&*root_set, &*head_set)))
let walk = index
.walk_revs(&head_positions, &[])
.take_until_roots(&root_positions);
let root_positions_set: HashSet<_> = root_positions.into_iter().collect();
let candidates = Box::new(RevWalkRevset { walk });
let predicate = PurePredicateFn(move |entry: &IndexEntry| {
entry
.parent_positions()
.iter()
.any(|parent_pos| root_positions_set.contains(parent_pos))
});
// TODO: Suppose heads include all visible heads, ToPredicateFn version can be
// optimized to only test the predicate()
Ok(Box::new(FilterRevset {
candidates,
predicate,
}))
} else if generation_from_roots == &GENERATION_RANGE_FULL {
let (dag_range_set, _) = self.collect_dag_range(&*root_set, &*head_set);
Ok(Box::new(dag_range_set))
let mut index_entries = index
.walk_revs(&head_positions, &[])
.descendants(&root_positions)
.collect_vec();
index_entries.reverse();
Ok(Box::new(EagerRevset { index_entries }))
} else {
// For small generation range, it might be better to build a reachable map
// with generation bit set, which can be calculated incrementally from roots:
// reachable[pos] = (reachable[parent_pos] | ...) << 1
let root_positions =
root_set.iter().map(|entry| entry.position()).collect_vec();
let walk = self
.walk_ancestors(&*head_set)
let mut index_entries = index
.walk_revs(&head_positions, &[])
.descendants_filtered_by_generation(
&root_positions,
to_u32_generation_range(generation_from_roots)?,
);
let mut index_entries = walk.collect_vec();
)
.collect_vec();
index_entries.reverse();
Ok(Box::new(EagerRevset { index_entries }))
}
Expand All @@ -605,12 +625,18 @@ impl<'index> EvaluationContext<'index> {
Ok(Box::new(EagerRevset { index_entries }))
}
ResolvedExpression::Roots(candidates) => {
let candidate_set = EagerRevset {
index_entries: self.evaluate(candidates)?.iter().collect(),
};
let (_, filled) = self.collect_dag_range(&candidate_set, &candidate_set);
let candidate_entries = self.evaluate(candidates)?.iter().collect_vec();
let candidate_positions = candidate_entries
.iter()
.map(|entry| entry.position())
.collect_vec();
let filled = self
.index
.walk_revs(&candidate_positions, &[])
.descendants(&candidate_positions)
.collect_positions_set();
let mut index_entries = vec![];
for candidate in candidate_set.iter() {
for candidate in candidate_entries {
if !candidate
.parent_positions()
.iter()
Expand Down Expand Up @@ -677,75 +703,6 @@ impl<'index> EvaluationContext<'index> {
}
}

fn walk_ancestors<'a, S>(&self, head_set: &S) -> RevWalk<'index>
where
S: InternalRevset<'a> + ?Sized,
{
let head_positions = head_set.iter().map(|entry| entry.position()).collect_vec();
self.index.walk_revs(&head_positions, &[])
}

fn walk_children<'a, 'b, S, T>(
&self,
root_set: &S,
head_set: &T,
) -> impl InternalRevset<'index> + 'index
where
S: InternalRevset<'a> + ?Sized,
T: InternalRevset<'b> + ?Sized,
{
let root_positions = root_set.iter().map(|entry| entry.position()).collect_vec();
let walk = self
.walk_ancestors(head_set)
.take_until_roots(&root_positions);
let root_positions: HashSet<_> = root_positions.into_iter().collect();
let candidates = Box::new(RevWalkRevset { walk });
let predicate = PurePredicateFn(move |entry: &IndexEntry| {
entry
.parent_positions()
.iter()
.any(|parent_pos| root_positions.contains(parent_pos))
});
// TODO: Suppose heads include all visible heads, ToPredicateFn version can be
// optimized to only test the predicate()
FilterRevset {
candidates,
predicate,
}
}

/// Calculates `root_set::head_set`.
fn collect_dag_range<'a, 'b, S, T>(
&self,
root_set: &S,
head_set: &T,
) -> (EagerRevset<'index>, HashSet<IndexPosition>)
where
S: InternalRevset<'a> + ?Sized,
T: InternalRevset<'b> + ?Sized,
{
let root_positions = root_set.iter().map(|entry| entry.position()).collect_vec();
let walk = self
.walk_ancestors(head_set)
.take_until_roots(&root_positions);
let root_positions: HashSet<_> = root_positions.into_iter().collect();
let mut reachable_positions = HashSet::new();
let mut index_entries = vec![];
for candidate in walk.collect_vec().into_iter().rev() {
if root_positions.contains(&candidate.position())
|| candidate
.parent_positions()
.iter()
.any(|parent_pos| reachable_positions.contains(parent_pos))
{
reachable_positions.insert(candidate.position());
index_entries.push(candidate);
}
}
index_entries.reverse();
(EagerRevset { index_entries }, reachable_positions)
}

fn revset_for_commit_ids(&self, commit_ids: &[CommitId]) -> EagerRevset<'index> {
let mut index_entries = vec![];
for id in commit_ids {
Expand Down