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fixup(#6037): actually fix the issue, #6388 failed to do so (#6429)

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Before this patch, the select! still retured immediately if `futs` was
empty. Must have tested a stale build in my manual testing of #6388.
This commit is contained in:
Christian Schwarz
2024-01-22 15:27:29 +01:00
committed by GitHub
parent 3290fb09bf
commit 15c0df4de7
1 changed files with 22 additions and 15 deletions
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37
pageserver/src/page_service.rs
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@@ -386,12 +386,18 @@ impl PageServerHandler {
/// Future that completes when we need to shut down the connection.
///
/// Reasons for need to shut down are:
/// - any of the timelines we hold GateGuards for in `shard_timelines` is cancelled
/// - task_mgr requests shutdown of the connection
/// We currently need to shut down when any of the following happens:
/// 1. any of the timelines we hold GateGuards for in `shard_timelines` is cancelled
/// 2. task_mgr requests shutdown of the connection
///
/// The need to check for `task_mgr` cancellation arises mainly from `handle_pagerequests`
/// where, at first, `shard_timelines` is empty, see <https://github.com/neondatabase/neon/pull/6388>
/// NB on (1): the connection's lifecycle is not actually tied to any of the
/// `shard_timelines`s' lifecycles. But it's _necessary_ in the current
/// implementation to be responsive to timeline cancellation because
/// the connection holds their `GateGuards` open (sored in `shard_timelines`).
/// We currently do the easy thing and terminate the connection if any of the
/// shard_timelines gets cancelled. But really, we cuold spend more effort
/// and simply remove the cancelled timeline from the `shard_timelines`, thereby
/// dropping the guard.
///
/// NB: keep in sync with [`Self::is_connection_cancelled`]
async fn await_connection_cancelled(&self) {
@@ -404,16 +410,17 @@ impl PageServerHandler {
// immutable &self). So it's fine to evaluate shard_timelines after the sleep, we don't risk
// missing any inserts to the map.
let mut futs = self
.shard_timelines
.values()
.map(|ht| ht.timeline.cancel.cancelled())
.collect::<FuturesUnordered<_>>();
tokio::select! {
_ = task_mgr::shutdown_watcher() => { }
_ = futs.next() => {}
}
let mut cancellation_sources = Vec::with_capacity(1 + self.shard_timelines.len());
use futures::future::Either;
cancellation_sources.push(Either::Left(task_mgr::shutdown_watcher()));
cancellation_sources.extend(
self.shard_timelines
.values()
.map(|ht| Either::Right(ht.timeline.cancel.cancelled())),
);
FuturesUnordered::from_iter(cancellation_sources)
.next()
.await;
}
/// Checking variant of [`Self::await_connection_cancelled`].