From 13476a8cf598770b501cf0b02a26725a6f5ce3d5 Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Thu, 5 Nov 2026 05:46:15 +0100
Subject: trees as member chose

---
 src/simtest/bench.rs | 10 +++++++++-
 src/swarm/tree.rs    | 25 ++++++++++++++++++++-----
 2 files changed, 29 insertions(+), 6 deletions(-)

(limited to 'src')

diff --git a/src/simtest/bench.rs b/src/simtest/bench.rs
index 40b413d..39e054e 100644
--- a/src/simtest/bench.rs
+++ b/src/simtest/bench.rs
@@ -600,7 +600,15 @@ async fn trees(out: &mut String, nodes: &[AppState], net: &crate::transport::sim
     };
     let mut latencies = Vec::new();
     for node in nodes {
-        latencies.extend(crate::swarm::tree::own_latencies(node, &latency).await);
+        // Each member's parent in this node's tree, as the member chose it.
+        let mut parents = std::collections::HashMap::new();
+        for member in nodes {
+            if member.local_id() != node.local_id() {
+                let chosen = crate::swarm::tree::own_parent(member, node.local_id()).await;
+                parents.insert(member.local_id().to_owned(), chosen);
+            }
+        }
+        latencies.extend(crate::swarm::tree::own_latencies(node, &parents, &latency).await);
     }
     let members: usize = latencies.iter().map(|l| l.members).sum();
     if members == 0 {
diff --git a/src/swarm/tree.rs b/src/swarm/tree.rs
index f04e442..29186d8 100644
--- a/src/swarm/tree.rs
+++ b/src/swarm/tree.rs
@@ -327,7 +327,9 @@ fn shape(
 
 /// How long our writes take to reach the members along our own tree, by link latency
 /// alone (the bench's, which knows each link's): the mean over the members it reaches
-/// (and the others do), against two other trees of ours. In one, each member's parent is
+/// (and the others do), against two other trees of ours. Our tree as the members chose
+/// their parents (`parents`, from `own_parent` on each): of members beyond our
+/// neighbours, we don't know the round trips their choice goes by. In one, each member's parent is
 /// chosen as now, but among those as close to us and as well placed (`rank`) by the
 /// exact latency, not the round-trip bucket it said; in the other, every member takes the fastest path over the links members
 /// reach (no tree computed alike everywhere gets below it). In milliseconds, one way.
@@ -340,11 +342,23 @@ pub(crate) struct Latencies {
     pub(crate) fastest: f64,
 }
 
+/// Our parent in `writer`'s tree, as we choose it (`parent`, by what we and our
+/// neighbours said); None if we have none, or no tree is known.
+#[cfg(test)]
+pub(crate) async fn own_parent(state: &AppState, writer: &str) -> Option<String> {
+    let (graph, distance) = distances(state, topology::pair_key(writer))?;
+    let known = known_reaches(state, &graph).await;
+    let reached = |by: &str, member: &str| known.reached(by, member);
+    let round_trip = |by: &str, member: &str| known.round_trip(by, member);
+    parent(&graph, &distance, &reached, &round_trip, state.local_id()).map(str::to_owned)
+}
+
 /// `Latencies` of our own tree, by `latency(from, to)` in milliseconds; None while the
 /// member list isn't known, or we aren't in it, or the tree reaches nobody.
 #[cfg(test)]
 pub(crate) async fn own_latencies(
     state: &AppState,
+    parents: &HashMap<String, Option<String>>,
     latency: &(dyn Fn(&str, &str) -> f64 + Sync),
 ) -> Option<Latencies> {
     let me = state.local_id();
@@ -360,10 +374,11 @@ pub(crate) async fn own_latencies(
     let now: HashMap<&str, Option<&str>> = members
         .iter()
         .map(|member| {
-            (
-                *member,
-                parent(&graph, &distance, &reached, &round_trip, member),
-            )
+            let chosen = match parents.get(*member) {
+                Some(chosen) => chosen.as_deref(),
+                None => parent(&graph, &distance, &reached, &round_trip, member),
+            };
+            (*member, chosen)
         })
         .collect();
     let faster: HashMap<&str, Option<&str>> = members
-- 
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