Why are duplicate event listeners/consumers supported?

Hi @RobWin,

As per this Javadoc, the Circuit breaker registry will either create a new circuit breaker or return an existing one with the same name. At the same time, I also noticed that the event listeners use an implementation of a List to keep track of all the registered event listeners.

Due to the dual behavior of Circuit Breaker registry, clients would now have to make sure that they don’t attach duplicate listeners. Use-case: If I’d like to attach an onEvent listener at the time of creation of circuit breaker, I risk registering the same listener multiple times.

Is there a reason to allow duplicate listeners? If this is not intended, we could use CopeOnWriteArraySet if we don’t expect the # of listeners to be large. But if it’s expected to have a large # of listeners, one option would be to use ConcurrentHashMap.

[dlsrb6342]

Yes right. You can consume EntryAddedEvent<CircuitBreaker>.

public class CustomRegistryEventConsumer<CircuitBreaker> implements RegistryEventConsumer<CircuitBreaker> {

    @Override
    public void onEntryAddedEvent(EntryAddedEvent<CircuitBreaker> entryAddedEvent) {
        entryAddedEvent.getAddedEntry().getEventPublisher().onEvent(......);
    }

    @Override
    public void onEntryRemovedEvent(EntryRemovedEvent<E> entryRemoveEvent) {    }

    @Override
    public void onEntryReplacedEvent(EntryReplacedEvent<E> entryReplacedEvent) {    }

}

[laksnv]

I think what I’m asking for is possible for Circuit Breaker Registry events, but not for Circuit Breaker instance events.

https://github.com/resilience4j/resilience4j/blob/2222e3e80ea6a4b58fe8e5b024aae03530e08ffe/resilience4j-circuitbreaker/src/main/java/io/github/resilience4j/circuitbreaker/CircuitBreakerRegistry.java#L71-L74