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doc: comment pass

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This commit is contained in:
Joonas Koivunen
2023-05-05 02:46:15 +03:00
parent 505febfc97
commit 4ef9f38bdd
1 changed files with 8 additions and 10 deletions
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18
pageserver/src/tenant.rs
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@@ -1452,17 +1452,20 @@ impl Tenant {
let mut rx = {
let mut g = timeline.delete_self.lock().await;
// see if we should join any existing attempt
let maybe_rx = if let Some(maybe_done) = g.as_ref() {
use timeline::MaybeDone;
// we got the lock, let's see if the previous attempt failed permanently
// TODO: is here some deadlock with the lock acquisition order?
match maybe_done {
MaybeDone::Done(Ok(())) => return Ok(()),
MaybeDone::Done(Err(e)) if e.is_permanent() => {
return Err(DeleteTimelineError::from(e))
}
MaybeDone::Pending(rx) => rx.upgrade(),
MaybeDone::Pending(rx) => {
// important: upgrading and later resubscription happens while holding the lock
rx.upgrade()
}
MaybeDone::Done(Err(_retryable)) => None,
}
} else {
@@ -1474,21 +1477,16 @@ impl Tenant {
} else {
// try another time
let (tx, rx) = tokio::sync::broadcast::channel(1);
// now anyone else racing will see the None
let rx = Arc::new(rx);
let this = self.clone();
let timeline = timeline.clone();
let rx = Arc::new(rx);
// sadly futures::future::FutureExt::shared requires clone, which we cannot give
// for tokio::task::JoinError
//
// TODO: this could be tenant scoped task_mgr task?
tokio::spawn({
let rx = rx.clone();
async move {
// to uphold the MaybeDone promise, we keep the channel alive *until* we've
// swapped the values
// swapped the MaybeDone::Pending -> MaybeDone::Done value
let tx = tx;
let rx = rx;