Re: CompletableFuture dependent ordering

It's similar for Scala Futures—happens-before can only be assumed for
chained effects, as "callbacks" registered to the same Future can
potentially run in parallel.

On Mon, Jan 4, 2021 at 11:31 PM Alex Otenko via Concurrency-interest <
[email protected]> wrote:

> I think you can only safely assume the happens-before between the
> computation of the value consumed and the computation consuming that value.
>
> That is, dependencies are ordered only through explicit chaining.
> CompletionStage doesn't seem to guarantee any other order.
>
> Alex
>
> On Mon, 4 Jan 2021, 22:32 Benjamin Manes via Concurrency-interest, <
> [email protected]> wrote:
>
>> Hi everyone,
>>
>> CompletableFuture maintains a Treiber stack for processing dependents,
>> such as "thenAccept" and "whenComplete" actions. I couldn't find a previous
>> discussion on this design decision. Can you please educate me on why a LIFO
>> stack was preferred over a FIFO queue?
>>
>> The current behavior seems less intuitive and a lack of awareness can
>> cause subtle surprises. While chaining against the dependent can resolve
>> these gotchas most of the time, there are scenarios where it is more
>> correct to work with the original future instance and to chain dependents
>> on the side. This has come up a few times regarding an asynchronous cache
>> and while I have educated users on this behavior, a workaround within the
>> cache would merely shift the pain by no longer returning the user's
>> supplied future instance. While I can understand the stack might have been
>> preferred as a more elegant implementation, I do not yet see why it would
>> be better by its external behavior.
>>
>> Thanks and happy new year.
>> _______________________________________________
>> Concurrency-interest mailing list
>> [email protected]
>> http://cs.oswego.edu/mailman/listinfo/concurrency-interest
>>
> _______________________________________________
> Concurrency-interest mailing list
> [email protected]
> http://cs.oswego.edu/mailman/listinfo/concurrency-interest
>


-- 
Cheers,
√

_______________________________________________
Concurrency-interest mailing list
[email protected]
http://cs.oswego.edu/mailman/listinfo/concurrency-interest