We had many discussions on this very hot topic. We really need to come with a good pattern, since a lot of people are expecting async features in CDI 2.0. 

So far, we have a fireAsync(...) on the firing side and an opt-in element on the observer side, to prevent accidental async call of an observer that needs to be called in the context of a transaction (for instance). 

Having to add this opt-in element on all our legacy observers will be very tedious, so we need to come with a better pattern here. 

We could add some information in the beans.xml, that would affect all the observers of the bean archive. Something that would tell "this bean archive globally supports asynchronous calls", that would act as a global opt-in. Then we also need a mean to opt-out observers one by one, because we'll have to deal with exceptions to this global rule. 

If there is no beans.xml, or a beans.xml without this information, the default behavior would be "asynch is not supported" for backward compatibility reasons. 

This individual opt-in / opt-out then becomes an override to a global rule set in the beans.xml, or defaulted to "async not supported". It can be expressed in the beans.xml itself, or with annotations on the observers. To deal with the potential incompatibility of adding an attribute to the existing @Observes annotation, we could propose a new annotation, something like @AsyncSupported(true) for instance. 

José

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