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make TaskHandle::next_task_event cancellation-safe

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If we get cancelled before jh.await returns we've take()n the join handle but
drop the result on the floor.

Fix it by setting self.join_handle = None after the .await

fixes https://github.com/neondatabase/neon/issues/3104
This commit is contained in:
Christian Schwarz
2022-12-14 19:26:06 +01:00
committed by Christian Schwarz
parent bf3ac2be2d
commit 10cd64cf8d
1 changed files with 9 additions and 3 deletions
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12
pageserver/src/walreceiver.rs
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@@ -126,15 +126,21 @@ impl<E: Clone> TaskHandle<E> {
match self.events_receiver.changed().await {
Ok(()) => TaskEvent::Update((self.events_receiver.borrow()).clone()),
Err(_task_channel_part_dropped) => {
TaskEvent::End(match self.join_handle.take() {
TaskEvent::End(match self.join_handle.as_mut() {
Some(jh) => {
if !jh.is_finished() {
warn!("sender is dropped while join handle is still alive");
}
jh.await
let res = jh
.await
.map_err(|e| anyhow::anyhow!("Failed to join task: {e}"))
.and_then(|x| x)
.and_then(|x| x);
// For cancellation-safety, drop join_handle only after successful .await.
self.join_handle = None;
res
}
None => {
// Another option is to have an enum, join handle or result and give away the reference to it