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Posted to notifications@pekko.apache.org by "He-Pin (via GitHub)" <gi...@apache.org> on 2026/06/28 16:09:13 UTC
[PR] fix: deliver stashed timer messages for UnboundedStash and UnrestrictedStash (#3258) [pekko]
He-Pin opened a new pull request, #3264:
URL: https://github.com/apache/pekko/pull/3264
### Motivation
`Timers` rewrites `actorCell.currentMessage` to the **unwrapped** timer message
before invoking the user's `receive`, so that `stash()` (which reads
`currentMessage` directly) captures the actual message rather than the internal
`TimerMsg` wrapper.
That rewrite was guarded by `this.isInstanceOf[Stash]`. But `Stash`,
`UnboundedStash` and `UnrestrictedStash` are **siblings** — they all extend
`UnrestrictedStash` / `StashSupport`, and `UnboundedStash`/`UnrestrictedStash`
are **not** subtypes of `Stash`. So for an actor mixing in `UnboundedStash` or
`UnrestrictedStash` directly, the guard was `false`, the rewrite was skipped,
and `stash()` captured the `TimerMsg` wrapper. On `unstashAll()` the wrapper was
intercepted again and discarded (the single-shot timer was already removed, or
the generation was stale for a periodic timer), so **the message was lost**.
The same guard also excluded the Java‑API stash actors (`AbstractActorWithStash`
and friends, via `AbstractActorStashSupport`), which have the same problem.
Fixes #3258.
### Modification
- Guard the `currentMessage` rewrite with `this.isInstanceOf[StashSupport]`
instead of `this.isInstanceOf[Stash]`. `StashSupport` is the common base of
all stash‑capable actors (`Stash`, `UnboundedStash`, `UnrestrictedStash`, and
the Java‑API stash classes), and it is exactly the set of actors whose
`stash()` reads `currentMessage` — so it is the precise, correct boundary.
- Expanded the explanatory comment so the sibling relationship and the
re‑stash/lost‑message mechanism are clear (keeping the original `#24557`
reference).
### Result
- Timer messages stashed with `UnboundedStash` or `UnrestrictedStash` (and the
Java‑API stash actors) are no longer lost on `unstashAll()`.
- Behavior for `Stash` is unchanged, and non‑stashing actors are unaffected
(the guard is still `false` for them).
- The change is a method‑body change in `Timers.aroundReceive`; **no public API
or binary‑compatibility change** (`actor / mimaReportBinaryIssues` is clean).
### Tests
- `sbt "actor-tests/testOnly org.apache.pekko.actor.TimerSpec org.apache.pekko.actor.TimersAndStashSpec"`
→ all passed.
- Added directional tests mirroring the existing `Stash` test, for
`UnboundedStash` and `UnrestrictedStash` (the latter with an explicit
deque‑based mailbox, since `UnrestrictedStash` does not declare
`RequiresMessageQueue`). Both **fail before the fix** (the stashed timer
message is lost: `expectMsg("scheduled")` times out) and pass after.
- `sbt "actor/mimaReportBinaryIssues"` → no binary issues.
### References
Fixes #3258
---
This is an original contribution to Apache Pekko, made under the Apache License
2.0 (i.e. the changes are now Apache licensed). No third-party or Akka-derived
code is included.
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Re: [PR] fix: deliver stashed timer messages for UnboundedStash and UnrestrictedStash (#3258) [pekko]
Posted by "He-Pin (via GitHub)" <gi...@apache.org>.
He-Pin merged PR #3264:
URL: https://github.com/apache/pekko/pull/3264
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Re: [PR] fix: deliver stashed timer messages for UnboundedStash and UnrestrictedStash (#3258) [pekko]
Posted by "He-Pin (via GitHub)" <gi...@apache.org>.
He-Pin commented on PR #3264:
URL: https://github.com/apache/pekko/pull/3264#issuecomment-4826745354
@pjfanning I think we can backport this to 1.7.0 ,wdyt
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Re: [PR] fix: deliver stashed timer messages for UnboundedStash and UnrestrictedStash (#3258) [pekko]
Posted by "He-Pin (via GitHub)" <gi...@apache.org>.
He-Pin commented on code in PR #3264:
URL: https://github.com/apache/pekko/pull/3264#discussion_r3488198550
##########
actor/src/main/scala/org/apache/pekko/actor/Timers.scala:
##########
@@ -55,8 +55,12 @@ trait Timers extends Actor {
case OptionVal.Some(m: AutoReceivedMessage) =>
context.asInstanceOf[ActorCell].autoReceiveMessage(Envelope(m, self, context.system))
case OptionVal.Some(m) =>
- if (this.isInstanceOf[Stash]) {
- // this is important for stash interaction, as stash will look directly at currentMessage #24557
+ if (this.isInstanceOf[StashSupport]) {
Review Comment:
https://github.com/apache/pekko/blob/main/actor/src/main/scala/org/apache/pekko/actor/Stash.scala
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