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<div class="moz-cite-prefix">On 03/16/2015 05:19 PM, Antoine
Sabot-Durand wrote:<br>
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cite="mid:37A9AF8E-D899-451A-B495-3B9A9A36B561@sabot-durand.net"
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<div class="">Le 16 mars 2015 à 10:33, Jozef Hartinger <<a
moz-do-not-send="true" href="mailto:jharting@redhat.com"
class="">jharting@redhat.com</a>> a écrit :</div>
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On 03/12/2015 01:56 PM, Antoine Sabot-Durand wrote:<br
class="">
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<blockquote
cite="mid:C24390F8-63BB-478A-A188-69CDEDE14026@sabot-durand.net"
type="cite" style="font-family: Helvetica; font-size:
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background-color: rgb(255, 255, 255);" class="">Hi all,
<div class=""><br class="">
</div>
<div class="">I compiled all the feedback and decision we
took regarding async events and updated the Google Doc
: <a moz-do-not-send="true"
href="https://docs.google.com/document/d/1Tm_fZWS6569YqCH9lGxuqBGzS9gfupic-vv1dyKCUxk/edit?usp=sharing"
class="">https://docs.google.com/document/d/1Tm_fZWS6569YqCH9lGxuqBGzS9gfupic-vv1dyKCUxk/edit?usp=sharing</a></div>
<div class=""><br class="">
</div>
<div class="">The following point stays open. I’d like to
close them (if possible) during the next meeting on
Tuesday</div>
<div class=""><br class="">
</div>
<div class="">1) Async delivery mechanism (comment by
Jozef)</div>
<div class="">Should we write in the spec about how
threads for events delivery should be used? Personally
I’d rather not: I think this should be let to
implementation, the specification should only describe
the expected behavior (concurrency or not). now I may
have missed something.</div>
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<span style="font-family: Helvetica; font-size: 12px;
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normal; letter-spacing: normal; line-height: normal;
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display: inline !important;" class="">We should not
specify technical details assuming we clearly define what
guarantees are/are not available regarding ordering,
visibility, concurrency, effects of exceptions,
CDI/security/transactional context propagation and perhaps
others I missed.</span><br style="font-family: Helvetica;
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<div>We’re saying the same : these will come from the specified
behavior ;)</div>
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<blockquote
cite="mid:C24390F8-63BB-478A-A188-69CDEDE14026@sabot-durand.net"
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<div class="">2) Exception Handling (comment by Jozef)</div>
<div class="">I didn’t write anything about exception and
we should decide what happens if an exception occurs in
an observer during async event dispatch. I think that it
shouldn’t impact other observers and that we should
stick to the way CompletionStage API works today.</div>
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<span style="font-family: Helvetica; font-size: 12px;
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background-color: rgb(255, 255, 255); float: none;
display: inline !important;" class="">What does it mean?
CompletionStage API allows you to handle (a single)
Exception. Would those exceptions be swallowed or provided
to the caller somehow?</span><br style="font-family:
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<div>suggestion are welcome. How could we handle multiple
exception at the caller level ?</div>
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I don't know. How did you plan to handle those in your proposal?<br>
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cite="mid:37A9AF8E-D899-451A-B495-3B9A9A36B561@sabot-durand.net"
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<blockquote
cite="mid:C24390F8-63BB-478A-A188-69CDEDE14026@sabot-durand.net"
type="cite" style="font-family: Helvetica; font-size:
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<div class=""><br class="">
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<div class="">3) Async event activation on both ends</div>
<div class="">We all agree that we need to explicitly fire
event asynchronously on the producer side (fireAsync()).
The discussion in 8.1 is about adding a way to accept
async call on the consumer (observer) side.</div>
<div class="">a) As events are often triggered in other
parts of the application than the parts that consume
them (most CDI framework lib fire events foe end user
code) preventing user to decide if an observer can be
called asynchronously could lead to issues and will
prevent library developper to use fireAsync() (in a
defensive coding approach).</div>
<div class="">b) On the other hand, when placed in the
same application, it’ll be very confusing for user to
have to fireAsync() and enable async observer to
activate this new feature.</div>
<div class=""><br class="">
</div>
<div class="">I propose an opt-out approach. We add
‘asyncSupported' member to ‘@Observes' annotation with
‘true’ as default value. So in case of b) the end user
won’t have to explicitly activate async on observer and
i case of a) user detecting issue coming from async
treatment of an event can explicitly declares one or
more observer not compatible with async resolution with
@Observes(asyncSupported=False)</div>
<div class=""><br class="">
</div>
<div class="">4) Support observer ordering with async
events</div>
<div class="">I think we should keep event ordering for
synchronous event and ignore this feature in async
event. I don’t see obvious use case to be async and
ordered.</div>
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<span style="font-family: Helvetica; font-size: 12px;
font-style: normal; font-variant: normal; font-weight:
normal; letter-spacing: normal; line-height: normal;
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background-color: rgb(255, 255, 255); float: none;
display: inline !important;" class="">if an observer O1
defines priority P1 and a different observer O2 defines P2
where P2 > P1 then it probably does that for a reason.
Most likely because O2 depends on the state changes
possibly performed by O1. I think this holds true no
matter if the event is fired synchronously or
asynchronously. Therefore, I think we should respect
priority in both cases.</span><br style="font-family:
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<br style="font-family: Helvetica; font-size: 12px;
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<span style="font-family: Helvetica; font-size: 12px;
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normal; letter-spacing: normal; line-height: normal;
orphans: auto; text-align: start; text-indent: 0px;
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word-spacing: 0px; -webkit-text-stroke-width: 0px;
background-color: rgb(255, 255, 255); float: none;
display: inline !important;" class="">In addition, the
observer ordering concept will be simpler if we treat
observers the same way in both sync and async.</span><br
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<div>That’s why your input is precious, previous discussion
brought us with the opposite pov. Personally the simpler to
implement is the right choice...</div>
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No, I mean simpler to explain and for users to take in.
Implementation complexity is way less important.<br>
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cite="mid:37A9AF8E-D899-451A-B495-3B9A9A36B561@sabot-durand.net"
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cite="mid:C24390F8-63BB-478A-A188-69CDEDE14026@sabot-durand.net"
type="cite" style="font-family: Helvetica; font-size:
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<div class="">5) Context propagation</div>
<div class=""> I understand that propagating contexts in
async event would impact easily context API. My only
concern here is to be define async event to keep this
feature possible.</div>
<div class=""><br class="">
</div>
<div class="">If I forgot points please comment this mail
and the doc so we can take final decision during next
meeting.</div>
<div class=""><br class="">
</div>
<div class="">Thank you</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
<div class="">Antoine</div>
<div class=""><br class="">
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