Config customization not respected

[Balázs Wermer]

Hi,

My intent is to use BlockHound during unit tests and I wanted to give some exceptions. If I understand correctly, with the provided BlockHoundIntegration class, BlockHound should not trigger for the provided configurations.

Expected Behavior

Should not throw BlockingOperationError.

Actual Behavior

It throws BlockingOperationError

Steps to Reproduce

I've provided a demo application: gradlew test
demo.zip

Your Environment

• JVM version (java -version): Oracle JDK 11.0.6
• OS and version (eg uname -a): Windows 10

[Simon Baslé]

I think that the usual "Mono is asynchronous" caveat applies here: BlockHound can't probably attach the execution phase of the lambda that invokes sleep to the fail() method (which only assembles the Mono without subscribing to it). So what's visible in the stack when the blocking call is attempted is the lamba, the subscribe call and the test method.

In order to allow this particular blocking call, you could use lambda$fail$0 as the method name.

Better yet, I'd advise you to extract that to a relevant method (let's call it example()), replace the lambda with the method's reference and configure BlockHound to allow said method:

@Component
public class BlockHoundDemo {
    
    public void example(Long l) {
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            throw new RuntimeException();
        }
    }

    public Mono<Long> fail() {
        return Mono.delay(Duration.ofSeconds(1)).doOnNext(this::example);
    }
}

and

builder.allowBlockingCallsInside("com.example.demo.BlockHoundDemo", "example");

[Balázs Wermer]

@simonbasle Thank you very much for the explanation indeed it works :)