ApplicationListener potentially invoked twice in circular reference with proxy [SPR-15452]

[spring-projects-issues]

Ilya Serkov opened SPR-15452 and commented

ApplicationEvent can be received by ApplicationListener two times.

Can be reproduced when these conditions coincide:

1. Have at least two listener beans
2. Listeners implement ApplicationListener
3. One listener has dependency on another listener (@Autowired)
4. Listeners must have cyclic dependency with another bean
5. Listener which invoked twice must have at least one @Transactional method

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Affects: 4.2.6

Referenced from: commits a2b3561, 9abf249

[spring-projects-issues]

Juergen Hoeller commented

Is one of the listener invocations going straight to the target object and one through the transactional proxy? Or are both going to the proxy?

I'm happy to consider more defensive handling there. However, please be aware that we only support cyclic dependencies in a lenient fashion, i.e. with various guarantees not applying. Our general recommendation certainly is to break the cyclic dependency, e.g. by factoring out a common delegate.

[spring-projects-issues]

Ilya Serkov commented

Is one of the listener invocations going straight to the target object and one through the transactional proxy? Or are both going to the proxy?

First case - "one going straight to the target object and one through the transactional proxy".

In
org.springframework.context.event.AbstractApplicationEventMulticaster.ListenerRetriever#applicationListeners
I can see two subscriptions for one listener - straight & proxy

[spring-projects-issues]

Juergen Hoeller commented

We're explicitly replacing a target ApplicationListener with its singleton proxy, if any: AbstractApplicationEventMulticaster checks this on registration through addApplicationListener now, where an existing listener object is given, whereas this cannot happen for registration by bean name in the first place.