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state-res: refactor tiebreaking logic for clarity

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Charles Hall 2024-11-06 12:29:08 -08:00 committed by strawberry
parent 97e2fb6df1
commit e31b9dd3a4
1 changed files with 39 additions and 13 deletions
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52
crates/ruma-state-res/src/lib.rs
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@ -1,6 +1,6 @@
use std::{
borrow::Borrow,
cmp::Reverse,
cmp::{Ordering, Reverse},
collections::{BinaryHeap, HashMap, HashSet},
hash::Hash,
};
@ -289,14 +289,44 @@ where
Fut: Future<Output = Result<(Int, MilliSecondsSinceUnixEpoch)>> + Send,
Id: Borrow<EventId> + Clone + Eq + Hash + Ord + Send,
{
#[derive(Eq, Ord, PartialEq, PartialOrd)]
#[derive(PartialEq, Eq)]
struct TieBreaker<'a, Id> {
inv_power_level: Int,
age: MilliSecondsSinceUnixEpoch,
power_level: Int,
origin_server_ts: MilliSecondsSinceUnixEpoch,
event_id: &'a Id,
}
impl<'a, Id> Ord for TieBreaker<'a, Id>
where
Id: Ord,
{
fn cmp(&self, other: &Self) -> Ordering {
// NOTE: the power level comparison is "backwards" intentionally.
// See the "Mainline ordering" section of the Matrix specification
// around where it says the following:
//
// > for events `x` and `y`, `x < y` if [...]
//
// <https://spec.matrix.org/v1.12/rooms/v11/#definitions>
other
.power_level
.cmp(&self.power_level)
.then(self.origin_server_ts.cmp(&other.origin_server_ts))
.then(self.event_id.cmp(other.event_id))
}
}
impl<'a, Id> PartialOrd for TieBreaker<'a, Id>
where
Id: Ord,
{
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
Some(self.cmp(other))
}
}
debug!("starting lexicographical topological sort");
// NOTE: an event that has no incoming edges happened most recently,
// and an event that has no outgoing edges happened least recently.
@ -317,12 +347,12 @@ where
for (node, edges) in graph {
if edges.is_empty() {
let (power_level, age) = key_fn(node.clone()).await?;
let (power_level, origin_server_ts) = key_fn(node.clone()).await?;
// The `Reverse` is because rusts `BinaryHeap` sorts largest -> smallest we need
// smallest -> largest
zero_outdegree.push(Reverse(TieBreaker {
inv_power_level: -power_level,
age,
power_level,
origin_server_ts,
event_id: node,
}));
}
@ -350,12 +380,8 @@ where
// Only push on the heap once older events have been cleared
out.remove(node.borrow());
if out.is_empty() {
let (power_level, age) = key_fn(parent.clone()).await?;
heap.push(Reverse(TieBreaker {
inv_power_level: -power_level,
age,
event_id: parent,
}));
let (power_level, origin_server_ts) = key_fn(parent.clone()).await?;
heap.push(Reverse(TieBreaker { power_level, origin_server_ts, event_id: parent }));
}
}