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Posted to notifications@pekko.apache.org by "He-Pin (via GitHub)" <gi...@apache.org> on 2026/06/20 12:05:30 UTC
[I] Throttle stage lacks supervisor strategy support for costCalculation exceptions [pekko]
He-Pin opened a new issue, #3101:
URL: https://github.com/apache/pekko/issues/3101
### Motivation
The `Throttle` stage's `costCalculation` function is called without any exception handling. If the user-provided cost function throws, the exception propagates directly and fails the stage unconditionally. Unlike other stages (e.g., `MapAsync`, `Log`, `Filter`), Throttle does not consult the `SupervisionStrategy` decider, preventing users from configuring Resume or Restart behavior for bad elements.
### Current behavior
In `Throttle.scala:71-84`, `costCalculation(elem)` is called without try-catch:
```scala
override def onPush(): Unit = {
val elem = grab(in)
val cost = costCalculation(elem) // No error handling
val delayNanos = tokenBucket.offer(cost)
...
}
```
### Proposed fix
1. Add `lazy val decider = inheritedAttributes.mandatoryAttribute[SupervisionStrategy].decider` in `createLogic`
2. Mix in `StageLogging` trait for error logging
3. Wrap `costCalculation(elem)` in try-catch, consult decider on exception:
- `Stop` → `failStage(ex)` (current behavior)
- `Resume`/`Restart` → log error and `pull(in)` to skip the element
4. Add tests verifying supervision directives work with Throttle
### References
- Inspired by Akka.NET [#6886](https://github.com/akkadotnet/akka.net/pull/6886)
- Similar pattern exists in Pekko's `MapAsync` (`Ops.scala:1301`) and `Log` (`Ops.scala:1542`)
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Re: [I] Throttle stage lacks supervisor strategy support for costCalculation exceptions [pekko]
Posted by "He-Pin (via GitHub)" <gi...@apache.org>.
He-Pin closed issue #3101: Throttle stage lacks supervisor strategy support for costCalculation exceptions
URL: https://github.com/apache/pekko/issues/3101
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Re: [I] Throttle stage lacks supervisor strategy support for costCalculation exceptions [pekko]
Posted by "He-Pin (via GitHub)" <gi...@apache.org>.
He-Pin closed issue #3101: Throttle stage lacks supervisor strategy support for costCalculation exceptions
URL: https://github.com/apache/pekko/issues/3101
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