D7793: rust-nodemap: mutable NodeTree data structure
gracinet (Georges Racinet)
phabricator at mercurial-scm.org
Mon Jan 6 19:26:08 UTC 2020
gracinet created this revision.
Herald added subscribers: mercurial-devel, kevincox, durin42.
Herald added a reviewer: hg-reviewers.
REVISION SUMMARY
Thanks to the previously indexing abstraction,
the only difference in the lookup algorithm is that we
don't need the special case for an empty NodeTree any more.
We've considered making the mutable root an `Option<Block>`,
but that leads to unpleasant checks and `unwrap()` unless we
abstract it as typestate patterns (`NodeTree<Immutable>` and
`NodeTree<Mutated>`) which seem exaggerated in that
case.
The initial copy of the root block is a very minor
performance penalty, given that it typically occurs just once
per transaction.
REPOSITORY
rHG Mercurial
BRANCH
default
REVISION DETAIL
https://phab.mercurial-scm.org/D7793
AFFECTED FILES
rust/hg-core/src/revlog/nodemap.rs
CHANGE DETAILS
diff --git a/rust/hg-core/src/revlog/nodemap.rs b/rust/hg-core/src/revlog/nodemap.rs
--- a/rust/hg-core/src/revlog/nodemap.rs
+++ b/rust/hg-core/src/revlog/nodemap.rs
@@ -148,16 +148,31 @@
}
}
-/// A 16-radix tree with the root block at the end
+/// A mutable 16-radix tree with the root block logically at the end
+///
+/// Because of the append only nature of our node trees, we need to
+/// keep the original untouched and store new blocks separately.
+///
+/// The mutable root `Block` is kept apart so that we don't have to rebump
+/// it on each insertion.
pub struct NodeTree {
readonly: Box<dyn Deref<Target = [Block]> + Send>,
+ growable: Vec<Block>,
+ root: Block,
}
impl Index<usize> for NodeTree {
type Output = Block;
fn index(&self, i: usize) -> &Block {
- &self.readonly[i]
+ let ro_len = self.readonly.len();
+ if i < ro_len {
+ &self.readonly[i]
+ } else if i == ro_len + self.growable.len() {
+ &self.root
+ } else {
+ &self.growable[i - ro_len]
+ }
}
}
@@ -179,8 +194,24 @@
}
impl NodeTree {
+ /// Initiate a NodeTree from an immutable slice-like of `Block`
+ ///
+ /// We keep `readonly` and clone its root block if it isn't empty.
+ fn new(readonly: Box<dyn Deref<Target = [Block]> + Send>) -> Self {
+ let root = readonly
+ .last()
+ .map(|b| b.clone())
+ .unwrap_or_else(|| Block::new());
+ NodeTree {
+ readonly: readonly,
+ growable: Vec::new(),
+ root: root,
+ }
+ }
+
+ /// Total number of blocks
fn len(&self) -> usize {
- self.readonly.len()
+ self.readonly.len() + self.growable.len() + 1
}
/// Main working method for `NodeTree` searches
@@ -191,11 +222,7 @@
&self,
prefix: NodePrefixRef<'p>,
) -> Result<Option<Revision>, NodeMapError> {
- let len = self.len();
- if len == 0 {
- return Ok(None);
- }
- let mut visit = len - 1;
+ let mut visit = self.len() - 1;
for i in 0..prefix.len() {
let nybble = prefix.get_nybble(i);
match self[visit].read(nybble) {
@@ -210,16 +237,18 @@
impl From<Vec<Block>> for NodeTree {
fn from(vec: Vec<Block>) -> Self {
- NodeTree {
- readonly: Box::new(vec),
- }
+ Self::new(Box::new(vec))
}
}
impl fmt::Debug for NodeTree {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
- let blocks: &[Block] = &*self.readonly;
- write!(f, "readonly: {:?}", blocks)
+ let readonly: &[Block] = &*self.readonly;
+ write!(
+ f,
+ "readonly: {:?}, growable: {:?}, root: {:?}",
+ readonly, self.growable, self.root
+ )
}
}
@@ -320,7 +349,9 @@
assert_eq!(
format!("{:?}", nt),
"readonly: \
- [[0: Rev(9)], [0: Rev(0), 1: Rev(9)], [0: Block(1), 1: Rev(1)]]"
+ [[0: Rev(9)], [0: Rev(0), 1: Rev(9)], [0: Block(1), 1: Rev(1)]], \
+ growable: [], \
+ root: [0: Block(1), 1: Rev(1)]",
);
}
@@ -352,4 +383,24 @@
assert_eq!(nt.find_hex(&idx, "00a"), Ok(Some(0)));
}
+ #[test]
+ fn test_mutated_find() -> Result<(), NodeMapError> {
+ let mut idx = TestIndex::new();
+ pad_insert(&mut idx, 9, "012");
+ pad_insert(&mut idx, 0, "00a");
+ pad_insert(&mut idx, 2, "cafe");
+ pad_insert(&mut idx, 3, "15");
+ pad_insert(&mut idx, 1, "10");
+
+ let nt = NodeTree {
+ readonly: sample_nodetree().readonly,
+ growable: vec![block![0: Rev(1), 5: Rev(3)]],
+ root: block![0: Block(1), 1:Block(3), 12: Rev(2)],
+ };
+ assert_eq!(nt.find_hex(&idx, "10")?, Some(1));
+ assert_eq!(nt.find_hex(&idx, "c")?, Some(2));
+ assert_eq!(nt.find_hex(&idx, "00")?, Some(0));
+ assert_eq!(nt.find_hex(&idx, "01")?, Some(9));
+ Ok(())
+ }
}
To: gracinet, #hg-reviewers
Cc: durin42, kevincox, mercurial-devel
More information about the Mercurial-devel
mailing list