CODEWITHSUNDEEP
kotlinproject-reactorkotlin-coroutines
Gabriel Kirsten
Gabriel Kirsten

Reputation: 11

What is the difference between await functions (coroutine) and subscribe on Reactor

I'm using Kotlin + Reactor (Mono and Flux) and I wanna know the difference between using await...() (from kotlin-coroutines-reactive) function and subscribe() (from Reactor). I brought two examples to show what I'm trying to do.

Example 1 (with await function):

@Test
internal fun test() = runBlockingTest {
    Mono.error<String>(IllegalStateException("exception"))
        .doOnError {
            print("error")
        }.awaitFirst().let {
            print("success")
        }
}

Output: "error" with the IllegalStateException stack trace.

Example 2 (with subscribe function):

@Test
internal fun test() = runBlockingTest {
    Mono.error<String>(IllegalStateException("exception"))
        .doOnError {
            print("error")
        }.subscribe {
            print("success")
        }
}

Output: Just "error".

Why example 1 shows the stack trace and example 2 doesn't show?

Thanks.

Upvotes: 1

Views: 1909

Answers (1)

Martin Tarj&#225;nyi
Martin Tarj&#225;nyi

Reputation: 9947

When you call subscribe on a reactive chain you decouple it from the main flow, it becomes independent and potentially asynchronous. Error is travelling on the reactive stream as a signal rather than as a traditionally thrown exception. In this case error handling is the responsibility of the reactive chain using operators like doOnError, onErrorMap, onErrorReturn, etc.

On the other hand Kotlin's await breaks this independence and attaches the reactive stream back to the main flow and lets you write reactive/asynchronous code as it would be imperative (e.g.: try-catch blocks, unwrapped function return types, etc.).

Upvotes: 1

Related Questions