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TaskHandle: tone down sender is dropped while join handle is still alive

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Rationale: see comments added as part of this commit.

fixes https://github.com/neondatabase/neon/issues/3339
This commit is contained in:
Christian Schwarz
2023-01-16 15:56:19 +01:00
committed by Christian Schwarz
parent e067cd2947
commit 48dd9565ac
1 changed files with 21 additions and 1 deletions
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22
pageserver/src/walreceiver.rs
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@@ -116,6 +116,10 @@ impl<E: Clone> TaskHandle<E> {
let join_handle = WALRECEIVER_RUNTIME.spawn(async move {
events_sender.send(TaskStateUpdate::Started).ok();
task(events_sender, cancellation_clone).await
// events_sender is dropped at some point during the .await above.
// But the task is still running on WALRECEIVER_RUNTIME.
// That is the window when `!jh.is_finished()`
// is true inside `fn next_task_event()` below.
});
TaskHandle {
@@ -132,7 +136,23 @@ impl<E: Clone> TaskHandle<E> {
TaskEvent::End(match self.join_handle.as_mut() {
Some(jh) => {
if !jh.is_finished() {
warn!("sender is dropped while join handle is still alive");
// Barring any implementation errors in this module, we can
// only arrive here while the task that executes the future
// passed to `Self::spawn()` is still execution. Cf the comment
// in Self::spawn().
//
// This was logging at warning level in earlier versions, presumably
// to leave some breadcrumbs in case we had an implementation
// error that would would make us get stuck in `jh.await`.
//
// There hasn't been such a bug so far.
// But in a busy system, e.g., during pageserver restart,
// we arrive here often enough that the warning-level logs
// became a distraction.
// So, tone them down to info-level.
//
// XXX: rewrite this module to eliminate the race condition.
info!("sender is dropped while join handle is still alive");
}
let res = jh