Fix Settings.InjectTopLevelFallback race condition
#7721
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Arkatufus
commented
Jul 2, 2025
Comment on lines
+52
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| while(true) | ||
| { | ||
| var oldConfig = _fallbackConfig.Value; | ||
| var newConfig = config.SafeWithFallback(oldConfig); | ||
| if (_fallbackConfig.CompareAndSet(oldConfig, newConfig)) | ||
| break; | ||
| } |
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Fix: Do not assign value to naked field directly, this can cause race condition if multiple Akka extensions running in multiple threads tries to start at the same time.
Scenario:
- Time 0
- Extension "A" reads
_fallbackConfigintoconfigA - Extension "B" reads
_fallbackConfigintoconfigB
- Extension "A" reads
- Time 1
- Extension "A" injects "akka.cluster.tools.singleton" into
configA - Extension "B" injects "akka.persistence.sql" into
configB
- Extension "A" injects "akka.cluster.tools.singleton" into
- Time 2
- Extension "A" writes
configAinto_fallbackConfig
- Extension "A" writes
- Time 3
- Extension "B" writes
configBinto_fallbackConfig
- Extension "B" writes
- Time 4
- Extension "A" reads "akka.cluster.tools.singleton" from
Settings.Config, getsNullReferenceExceptionbecause it got clobbered by Extension "B"
- Extension "A" reads "akka.cluster.tools.singleton" from
Aaronontheweb
approved these changes
Jul 2, 2025
| private readonly Config _userConfig; | ||
| //internal static readonly Config AkkaDllConfig = ConfigurationFactory.FromResource<Settings>("Akka.Configuration.Pigeon.conf"); | ||
| private Config _fallbackConfig; | ||
| private readonly AtomicReference<Config> _fallbackConfig; |
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yeah, this is a much simpler fix than what I was imagining
Comment on lines
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to
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| while(true) | ||
| { | ||
| var oldConfig = _fallbackConfig.Value; | ||
| var newConfig = config.SafeWithFallback(oldConfig); | ||
| if (_fallbackConfig.CompareAndSet(oldConfig, newConfig)) | ||
| break; | ||
| } |
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Fixes #7426
Changes
AtomicReference<T>to enforce thread safety