Support `@CircuitBreaker` on suspend functions (including `suspend fun` fallback methods) in Spring Boot 2

[efemoney]

Resilience4j version: 1.7.1 Java version: 16 kotlin version: 1.5.30

@CircuitBreaker does not work with bean suspend functions even when it boasts Kotlin Coroutines support.

First, FallbackMethod.create(...) will always fail to find the fallback method because of how kotlin inserts a kotlin.coroutines.Continuation<T> as the last parameter of suspend functions. This is illustrated below.

@Service class MyBean {

  @CircuitBreaker("breakerName", fallbackMethod = "aFallbackMethod")
  suspend fun aMethod(aParam: String): String { ... }

  suspend fun aFallbackMethod(theParam: String, error: Throwable): String { ... }
}

For the above bean the runtime method signatures are

aMethod(String, Continuation): Object & aFallbackMethod(String, Throwable, Continuation): Object

which is why the fallback method cannot be determined, because the throwable is not the last parameter in the fallback function.

Also, being a suspend function, its inherently asynchronous and needs to be explicitly handled (or wrapped somehow) inside of CircuitBreakerAspect to function correctly

[RobWin]

Hi, the Spring Boot module does not support Kotlin right now. You can only use resilience4j-kotlin directly. But feel free to create a PR to improve the Spring Boot Kotlin support.

[efemoney]

@RobWin Sounds good. I will open a PR soon for this.

[vinmorel]

Hi, on a similar note, does the micronaut module not support kotlin suspend functions as well? Having trouble on this side of things too.

[AAverin]

Was there a PR made and issue resolved? We would love to switch from CompletalbeFuture to suspend functions in our services.

[RobWin]

No

[sangyongchoi]

Hi, I have a question. If I use the resiliency4j-kotlin module, can I use it as below?

gradle

dependencies {
    implementation("org.springframework.cloud:spring-cloud-starter-circuitbreaker-resilience4j")
    implementation("io.github.resilience4j:resilience4j-kotlin:1.7.0")
}

kotlin

@CircuitBreaker(
    name = "myCircuitBreaker",
    fallbackMethod = "fallback"
)
suspend fun get() {
}

What I'm worried about is whether the Annotation and suspend function work normally when used together. If not, should I use it as below?

suspend fun get() {
     myCircuitBreaker.executeSuspendFunction {
     }
}

[RobWin]

Hi,

the annotations are not working with suspending functions yet.

[sangyongchoi]

@RobWin thank you for answer. not working when not add resilience4j-kotlin with exception that not exists method(Continuation) but seems to working when add resilience4j-kotlin dependency. If it's my misunderstanding, can you tell me why?

thank you :)

[RobWin]

resilience4j-kotlin only adds extension functions to decorate suspending functions. The module does not enhance the AOP/annotations capabilities of resilience4j-springboot2.

[sangyongchoi]

@RobWin thank you for answer. seems to working with suspend function in demo example repo it's my misunderstanding ?

added comment I guess annotation not working when fallback method is suspending function. seems to annotation working when fallback method is non suspending function.

[gmmoreira]

@sangyongchoi giving feedback, I just tested using latest Spring Boot 3 and Resilience4j Spring Boot 3 lib and the annotations doesn't work on suspend functions, using fallback methods didn't make any difference.

For now I'm just using decorateSuspend and executeSuspend functions from Kotlin addon lib.

[mobin102]

@gmmoreira can you please write an example of how to use decorateSuspend and executeSuspend spring boot