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proxy: fix memory leak again (#5909)

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## Problem

The connections.join_next helped but it wasn't enough... The way I
implemented the improvement before was still faulty but it mostly worked
so it looked like it was working correctly.

From [`tokio::select`
docs](https://docs.rs/tokio/latest/tokio/macro.select.html):
> 4. Once an <async expression> returns a value, attempt to apply the
value to the provided <pattern>, if the pattern matches, evaluate
<handler> and return. If the pattern does not match, disable the current
branch and for the remainder of the current call to select!. Continue
from step 3.

The `connections.join_next()` future would complete and `Some(Err(e))`
branch would be evaluated but not match (as the future would complete
without panicking, we would hope). Since the branch doesn't match, it's
disabled. The select continues but never attempts to call `join_next`
again. Getting unlucky, more TCP connections are created than we attempt
to join_next.

## Summary of changes

Replace the `Some(Err(e))` pattern with `Some(e)`. Because of the
auto-disabling feature, we don't need the `if !connections.is_empty()`
step as the `None` pattern will disable it for us.
This commit is contained in:
Conrad Ludgate
2023-11-23 19:11:24 +00:00
committed by GitHub
parent 582a42762b
commit a56fd45f56
2 changed files with 24 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
proxy/src/bin/pg_sni_router.rs
View File

@@ -168,9 +168,18 @@ async fn task_main(
.instrument(tracing::info_span!("handle_client", ?session_id))
);
}
Some(Err(e)) = connections.join_next(), if !connections.is_empty() => {
if !e.is_panic() && !e.is_cancelled() {
warn!("unexpected error from joined connection task: {e:?}");
// Don't modify this unless you read https://docs.rs/tokio/latest/tokio/macro.select.html carefully.
// If this future completes and the pattern doesn't match, this branch is disabled for this call to `select!`.
// This only counts for this loop and it will be enabled again on next `select!`.
//
// Prior code had this as `Some(Err(e))` which _looks_ equivalent to the current setup, but it's not.
// When `connections.join_next()` returned `Some(Ok(()))` (which we expect), it would disable the join_next and it would
// not get called again, even if there are more connections to remove.
Some(res) = connections.join_next() => {
if let Err(e) = res {
if !e.is_panic() && !e.is_cancelled() {
warn!("unexpected error from joined connection task: {e:?}");
}
}
}
_ = cancellation_token.cancelled() => {

15
proxy/src/proxy.rs
View File

@@ -294,9 +294,18 @@ pub async fn task_main(
}),
);
}
Some(Err(e)) = connections.join_next(), if !connections.is_empty() => {
if !e.is_panic() && !e.is_cancelled() {
warn!("unexpected error from joined connection task: {e:?}");
// Don't modify this unless you read https://docs.rs/tokio/latest/tokio/macro.select.html carefully.
// If this future completes and the pattern doesn't match, this branch is disabled for this call to `select!`.
// This only counts for this loop and it will be enabled again on next `select!`.
//
// Prior code had this as `Some(Err(e))` which _looks_ equivalent to the current setup, but it's not.
// When `connections.join_next()` returned `Some(Ok(()))` (which we expect), it would disable the join_next and it would
// not get called again, even if there are more connections to remove.
Some(res) = connections.join_next() => {
if let Err(e) = res {
if !e.is_panic() && !e.is_cancelled() {
warn!("unexpected error from joined connection task: {e:?}");
}
}
}
_ = cancellation_token.cancelled() => {