[cdi-dev] What, if any, guarantees are made about invoking asynchronous event observer methods?

Martin Kouba mkouba at redhat.com
Fri May 12 02:39:49 EDT 2017

Dne 11.5.2017 v 21:30 Laird Nelson napsal(a):
> I'm using CDI 2.0 and Weld 3.0.0.CR2 in "SE mode".
> If I fire an asynchronous event without any special notification
> options, my understanding is that the container will arrange for that
> event to be delivered to asynchronous observers.
> Is (appropriate) asynchronous observer method invocation guaranteed to
> happen at some point?  Section 10.2.2 seems to hint that it is:
> "Event fired [sic] with the fireAsync() method is [sic] fired
> asynchronously. *All the resolved asynchronous observers* (as defined in
> Observer resolution) *are called* in one or more different threads."
> To me, this says that if I use fireAsync() to fire an event, then if I
> have a (resolved) asynchronous observer method for it it will be
> notified before the container closes no matter what.

I think it's undefined. And I don't believe it would be reasonable to 
block the container shutdown because of an async observer method waiting 
for notification. The spec is clear that the container must destroy all 
contexts when an application is stopped. And if we destroy the contexts 
then the bean declaring the observer or its dependencies might be in 
inconsistent state.

> (I believe I am observing a race condition somewhere in here that might
> show that Weld's default asynchronous event delivery machinery does not
> actually get around to delivering the event I've queued up before the
> container closes.  Sometimes the event is received, sometimes it is
> not.  Obviously if there is no such guarantee this could be permitted
> behavior.)
> Best,
> Laird
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Martin Kouba
Senior Software Engineer
Red Hat, Czech Republic

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