如何捕获反应流取消信号？

Question

I want to do something finally after stream terminates for any reason including cancellation, and I found the doFinally method, but it dose not work when cancellation, because https://github.com/reactor/reactor-core/issues/1090#issuecomment-367633241 show :

Cancellation travels only upstream

So, how to capture the cancel signal?

There is my code:

    public Mono<Void> myFunction() {
        return Mono.just("hello")
                .flatMap(s -> foo(s))
                .doFinally(signalType -> {
                    // do something finally, but the doFinally won't be called
                    System.out.println(signalType);
                });
    }

    // some other library's function that I cant not modify any way
    public Mono<Void> foo(String s) {
        // return a reactive stream, and will cancel it after it be subscribed, like:
        return Mono.just(s)
                .doOnSubscribe(subscription -> subscription.cancel())
                .then();
    }

Answer 1

You can't in that particular arrangement, because the foo() method/library seems to manage the subscription (the cancellation) itself, instead of leaving that responsibility to the consumer. Managing the subscription like that is thus not necessarily a good thing.