Re: Counter-intuitive behavior of CompleteableFuture

The timeout is applied to the STEP2 future which completes it
exceptionally. This causes it to not run the mapping function for a result,
as it was completed prior to that being triggered. You can use copy() to
decouple the source from the timeout if you want both to complete; e.g.
cache a long running value but fail a consumer if taking to long.

On Thu, May 20, 2021 at 5:31 AM Michał Górniewski via Concurrency-interest <
[email protected]> wrote:

> With following code:
>
> ------------------------------
> public static void main(String[] args) {
>     CompletableFuture<String> initial = new CompletableFuture<>();
>
>     CompletableFuture<String> withSteps = initial
>             .thenApply(s -> {
>                 System.out.println("STEP1: " + s);
>                 return s;
>             })
>             .thenApply(s -> {
>                 System.out.println("STEP2: " + s);
>                 return s;
>             });
>
>     CompletableFuture<String> timeout = withSteps;
>
>     timeout.whenComplete((s, throwable) ->
> System.out.println("TIMEOUT: " + throwable));
>
>     timeout.completeExceptionally(new RuntimeException("TIMEOUT"));
>     initial.complete("SUCCESS");
> }
> ------------------------------
>
> I got output like this:
>
> ------------------------------
> TIMEOUT: java.lang.RuntimeException: TIMEOUT
> STEP1: SUCCESS
> ------------------------------
>
> I don't understand why "STEP2" is not executed in this case. Is this
> expected?
> For me this API is confusing and may create issues like this:
> https://github.com/resilience4j/resilience4j/issues/1427
>
> Thanks,
> Michał Górniewski
> _______________________________________________
> Concurrency-interest mailing list
> [email protected]
> http://cs.oswego.edu/mailman/listinfo/concurrency-interest
>

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