[cdi-dev] [JBoss JIRA] (CDI-499) Firing events asynchronously

Antoine Sabot-Durand (JIRA) issues at jboss.org
Wed Jan 21 05:12:49 EST 2015

Antoine Sabot-Durand created CDI-499:

             Summary: Firing events asynchronously 
                 Key: CDI-499
                 URL: https://issues.jboss.org/browse/CDI-499
             Project: CDI Specification Issues
          Issue Type: Feature Request
          Components: Events
    Affects Versions: 1.2.Final
            Reporter: Antoine Sabot-Durand

We should allow a way to fire event asynchronously. This mechanism should leverage new async API in JDK8 especially the {{CompletionStage}} interface.
Our proposal is: 

h2. 1. Add {{fireAsync()}} method to {{Event}} and {{BeanManager}}
Signature of the method on {{Event<T>}} would be
<U extends T> CompletionStage<U> fireAsync(U event);

Signature on {{BeanManager}} would be
<T> CompletionStage<T> fireAsyncEvent(T event, Annotation... qualifiers)

h2. 2. Add an {{asyncSupported()}} member to {{@Observes}}
For backward compatibility reason the possibility to invoke an observer asynchronously should be let to the observer (legacy observers should be called synchronously). We propose to add the boolean {{asyncSupported()}} member with the {{false}} default value to support this backward compatibility aspect.

h2. 3. Observer bound to a transaction phase
these observer will be invoked in the right transaction phase but asynchronously

h2. 4. Event Ordering
Should we decide to add events ordering in CDI 2.0, the order will be keep in asynchronous observer notification. If there are amix of synchronous and asynchronous observer, asynchronous will be called first in order, then synchronous in their order (async has priority on sync).

h2 5. Event state (payload mutability)
We'll keep payload mutability with async events (but should explicitly specify it). That means  that we should guarantee the event state consistency between observers and in case of ordered observers the fact that observer N+1 get the event state at the end of observer N.  

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