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B2 fix batch: a lost record race is progress, a refused write is not

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replace_generation now tells a lost compare-exchange (another writer moved the
store: the pass ends and re-reads) from a write the store refused.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
This commit is contained in:
Meta Vens 2026-09-30 04:27:03 +02:00
commit 74e7ed495e
1 changed files with 18 additions and 18 deletions
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36
src/control_plane.rs
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@ -4483,25 +4483,23 @@ impl Engine {
}
/// Replace an admitted generation by compare-exchange against the envelope
/// that was read.
/// that was read. `Ok(false)` is a lost race: another writer moved the
/// record, so the caller's snapshot is stale. `Err` is a write the store
/// refused, which changed nothing.
fn replace_generation(
&self,
seen: &Stored<AdmittedGeneration>,
next: &AdmittedGeneration,
now: u64,
) -> Result<()> {
ensure!(
SingleFileMessagePackBackingStore::new(&self.options.state_store).compare_exchange(
&[CultCacheExpectedEnvelope {
r#type: AdmittedGeneration::TYPE.into(),
key: seen.value.target.clone(),
current: Some(seen.envelope.clone()),
}],
&[admitted_envelope(next, now)?],
)?,
"admitted generation changed before its write"
);
Ok(())
) -> Result<bool> {
Ok(SingleFileMessagePackBackingStore::new(&self.options.state_store).compare_exchange(
&[CultCacheExpectedEnvelope {
r#type: AdmittedGeneration::TYPE.into(),
key: seen.value.target.clone(),
current: Some(seen.envelope.clone()),
}],
&[admitted_envelope(next, now)?],
)?)
}
/// Say a fault once while it lasts, under `key`.
@ -5884,12 +5882,14 @@ impl Engine {
("failed", due)
}
};
// Progress is a record that landed. A write the store refused changed
// nothing: the pass reports no progress, the scheduler sleeps if nothing
// else moved, and the in-memory wait spaces the next challenge.
// Progress is a store that changed: our record landed, or another
// writer beat it (the snapshot is stale either way, so the pass ends).
// A write the store refused changed nothing: no progress, the scheduler
// sleeps if nothing else moved, and the in-memory wait spaces the next
// challenge.
let record_key = format!("route-record:{}", current.value.target);
match self.replace_generation(current, &next, now) {
Ok(()) => {
Ok(_) => {
self.challenge_wait
.lock()
.expect("challenge wait mutex")