[cdi-dev] [JBoss JIRA] (CDI-563) Event.fireAsync() - clarify the usage of the returned CompletionStage

[Antoine Sabot-Durand (JIRA)]

    [ https://issues.jboss.org/browse/CDI-563?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13119253#comment-13119253 ] 

Antoine Sabot-Durand commented on CDI-563:
------------------------------------------

I'm not sure to get your point.
We are using API (and impl) provided by Java 8. Async event behavior won't be more confusing than this standard API.

Regarding context propagation as we said we won't support it, I don't think it'll be a problem

> Event.fireAsync() - clarify the usage of the returned CompletionStage
> ---------------------------------------------------------------------
>
>                 Key: CDI-563
>                 URL: https://issues.jboss.org/browse/CDI-563
>             Project: CDI Specification Issues
>          Issue Type: Clarification
>          Components: Events
>    Affects Versions: 2.0-EDR1
>            Reporter: Martin Kouba
>
> So far {{CompletionStage}} is only mentioned in "10.5.1. Handling multiple exceptions thrown during an asynchronous event" and the {{Event.fireAsync()}} javadoc is too general. However, the {{CompletionStage}} itself does not define an unambiguous contract for its methods. E.g. what thread is used to execute a given callback? Or what's the _"stage's default asynchronous execution facility"_? I believe this is left on implementors. In Weld 3.0 Alpha we're using {{CompletableFuture}} under the hood, and its more concrete in this area, e.g.:
> {quote}
> * Actions supplied for dependent completions of _non-async_ methods may be performed by the thread that completes the current CompletableFuture, or by any other caller of a completion method.
> {quote}
> So as a result, if an async delivery is finished before a sync dependent action is registered, the callback is executed in the caller thread:
> {code:java}
> event.fireAsync(new Message()).thenAccept((m) -> System.out.println("This might be executed in a caller thread or in a different thread!"));
> {code}
> And this might be confusing. Especially from the context propagation point of view. I think the spec should clarify the contract of a returned {{CompletionStage}}.



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