Re: Counter-intuitive behavior of CompleteableFuture

What bothers me here is API of CompletableFuture itself, e.g:

public CompletableFuture<ProcessingOutput>
executeProcessing(Function<Path, ProcessingOutput> processor) {
    Path data = prepareData();
    return CompletableFuture.supplyAsync(() -> processor.apply(data),
processingExecutor)
            .whenComplete((o, ex) -> cleanup(data));
}

Callers of this method may just break cleanup, without even knowing
about this, but simply calling complete() on returned CF. But it seems
that nothing can be done about it.

czw., 20 maj 2021 o 14:40 Benjamin Manes <[email protected]> napisał(a):
>
> 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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