Hi all, I still don't agree with us effectively removing the "intercepting" use-case without adding a solid proposal/roadmap on how we plan to re-introduce this behavior in the near future - if the "Events" functionality wasn't in "Beta", this would be completely unacceptable IMO. But I don't have a concern with Alex's proposal (on its own) given that we all are agreeing to re-introduce the pruned "interceptor" functionality through a different proposal.
Best, Adnan Hemani On Mon, Nov 17, 2025 at 11:33 AM Dmitri Bourlatchkov <[email protected]> wrote: > Hi Yufei, > > Sorry, I misread your previous message. I think we're in agreement on > "interceptors" . Sorry about the confusion. > > Cheers, > Dmitri. > > On 2025/11/17 15:23:47 Dmitri Bourlatchkov wrote: > > Hi Yufei, > > > > I have to disagree on the "interceptor" point. As I commented > previously, I > > do believe that event listeners should not be used as interceptors. > > Specifically, exceptions and return values from event listeners should > not > > affect the processing of the request in Polaris (i.e. requests should > work > > as if no event listeners are present). > > > > I do not mind adding a separate interceptor SPI with well-defined > > proceed/abort semantics. My objection relates only to overloading current > > event listeners with the assumption that they can influence request > > processing in the server. > > > > Thanks, > > Dmitri. > > > > On Sat, Nov 15, 2025 at 4:47 PM Yufei Gu <[email protected]> wrote: > > > > > To move forward, we may decouple two debates. Supporting multiple > listeners > > > is generally uncontroversial, while whether events should act as > > > interception points has mixed thoughts. > > > > > > We may proceed with async multiple listeners as an enhancement. These > > > listeners should be notification-only, independent, and non-blocking. > > > > > > For those who rely on sync/blocking hooks, we can open a dedicated > > > discussion about creating a separate SPI for policy or > server-interception > > > logic, which gives us a clean and explicit place for policy > enforcement, or > > > general data governance use cases, without overloading the event API. > > > > > > Yufei > > > > > > > > > On Fri, Nov 14, 2025 at 1:43 PM Adnan Hemani > > > <[email protected]> wrote: > > > > > > > Hi all, > > > > > > > > +1 to Eric's statements: "Events as they stand today can and do > function > > > as > > > > injection points for arbitrary code" and "if we intend to change the > > > > functionality / scope of events we > > > > should do that in clear terms and with a well-considered design" > > > > > > > > I likely will not be supporting any proposal where the current > > > synchronous > > > > functionality is no longer allowed as part of the events feature > (unless > > > > there is compelling evidence to back up the claims that this > > > functionality > > > > cannot be used today or will not be useful in the future), although > I am > > > > still in heavy support of adding functionality for multiple event > > > > listeners. > > > > > > > > Best, > > > > Adnan Hemani > > > > > > > > On Thu, Nov 13, 2025 at 8:01 AM Alexandre Dutra <[email protected]> > > > wrote: > > > > > > > > > > Why is this behavior change being coupled with a proposal to > support > > > > > multiple event listeners, anyway? > > > > > > > > > > My proposal couples both because 1) synchronous listeners could > > > > > monopolize the event loop (cf. AWS CloudWatch sink), and 2) a > > > > > composite listener is imho not an elegant solution to the multiple > > > > > listeners problem. > > > > > > > > > > Thanks, > > > > > Alex > > > > > > > > > > On Thu, Nov 13, 2025 at 12:35 PM Eric Maynard < > > > [email protected]> > > > > > wrote: > > > > > > > > > > > > It's true that the listener methods return void -- I think they > > > should > > > > > > probably have always returned events -- but that doesn't mean you > > > can't > > > > > do > > > > > > interesting things with the current (blocking) methods. Besides > the > > > > > > already-given example of throwing an exception from within a > > > listener, > > > > > some > > > > > > listener methods take an immutable parameter that has mutable > objects > > > > > held > > > > > > within. Michael rightly points out above that even an > > > > accidentally-thrown > > > > > > exception may stop processing, which in some cases can be > valuable. > > > > > > > > > > > > Why is this behavior change being coupled with a proposal to > support > > > > > > multiple event listeners, anyway? Yufei brought the issue of > multiple > > > > > > listeners up on the original PR > > > > > > < > https://github.com/apache/polaris/pull/922#discussion_r1985409710> > > > > and > > > > > > IIRC there were some followup discussions about a way to wrap > > > multiple > > > > > > listeners in one. I think it can be done, and might be useful. > But I > > > > > > suspect that this can be done without losing functionality, and > > > further > > > > > it > > > > > > seems that if we intend to change the functionality / scope of > events > > > > we > > > > > > should do that in clear terms and with a well-considered design. > > > > > > > > > > > > --EM > > > > > > > > > > > > On Thu, Nov 13, 2025 at 4:24 AM Alexandre Dutra < > [email protected]> > > > > > wrote: > > > > > > > > > > > > > Hi all, > > > > > > > > > > > > > > > Events as they stand today can and do function as injection > > > points > > > > > for > > > > > > > arbitrary code. > > > > > > > > > > > > > > I don't think so? How would one "hook into various parts of the > > > > > > > Polaris functionality" with this API? All listener methods take > > > > > > > immutable parameters and return nothing: this opinionated > design > > > > > > > forbids "arbitrary code" to be injected. I cannot, for > instance, > > > > > > > intercept some endpoint and modify the REST response to my > needs. > > > > > > > > > > > > > > Whatever the original intent of this API was, it's a fact that > in > > > its > > > > > > > current state it is not suitable for implementing > interceptors. My > > > > > > > proposal doesn't change the statu quo, only makes it official. > > > > > > > > > > > > > > Thanks, > > > > > > > Alex > > > > > > > > > > > > > > On Thu, Nov 13, 2025 at 2:32 AM Eric Maynard < > > > > [email protected] > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > I mentioned Java and React because they're very clear > examples of > > > > how > > > > > > > > the term "event listener" is generally understood, and Spark > only > > > > > because > > > > > > > > it was referenced by name in the initial proposal email. > Spark's > > > > > > > > listeners *have > > > > > > > > to be* async due to the nature of Spark as something that > runs > > > > across > > > > > > > > threads (/ VMs / processes). That said, it's still possible > if > > > not > > > > > common > > > > > > > > to implement a Spark listener that does something like cancel > > > > > > > long-running > > > > > > > > jobs. This is neither here nor there, though -- my point is > not > > > > that > > > > > we > > > > > > > > should copy Spark or React, but rather that to say events > are not > > > > > > > intended > > > > > > > > as injection points is perhaps revisionist history. > > > > > > > > > > > > > > > > The original design proposal was sent out with this passage: > > > > > > > > > > > > > > > > It would be useful to add a generic event listener interface > to > > > > > Polaris, > > > > > > > > consistent with other OSS projects. Users of the project may > > > > require > > > > > > > > additional functionality that doesn't have a clear enough > value > > > > > > > proposition > > > > > > > > to be in OSS. Instead, there can be event listeners that let > you > > > > hook > > > > > > > into > > > > > > > > various parts of the Polaris functionality (i.e. "before > table > > > > > commit") > > > > > > > > without OSS prescribing the limits of the extra > functionality. > > > > > > > > > > > > > > > > > > > > > > > > Events as they stand today can and do function as injection > > > points > > > > > for > > > > > > > > arbitrary code. It's my understanding that they were > designed to > > > > > serve > > > > > > > this > > > > > > > > role and that this aspect of the design was in part a > reaction to > > > > > debates > > > > > > > > happening at the time around API stability, refactors, and > > > > extension > > > > > > > > points. We were still dreaming about killing CallContext. The > > > > Iceberg > > > > > > > > events proposal did not yet exist. And at least my own > > > endorsement > > > > of > > > > > > > > the proposal / PR was contingent on this functionality. > > > > > > > > > > > > > > > > If we as a community align on removing this functionality > from > > > the > > > > > events > > > > > > > > framework, we should be intentional about that. Currently the > > > > > (re)design > > > > > > > of > > > > > > > > events seems to be taking place across many email threads > without > > > > > clear > > > > > > > > arguments about what the framework should support or why. > > > > > > > > > > > > > > > > --EM > > > > > > > > > > > > > > > > On Wed, Nov 12, 2025 at 1:08 PM Alexandre Dutra < > > > [email protected] > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > Hi all, > > > > > > > > > > > > > > > > > > Several people mentioned Spark event listeners. After > looking > > > > more > > > > > > > > > closely into this feature, I think it actually looks very > > > similar > > > > > to > > > > > > > > > what I'm proposing: > > > > > > > > > > > > > > > > > > - The primary intended use cases that I could find are : > > > > monitoring > > > > > > > > > job progress, tracking stages and task completion, > gathering > > > > > metrics > > > > > > > > > [1]. > > > > > > > > > > > > > > > > > > - Events are distributed asynchronously via an internal > > > component > > > > > > > > > called SparkListenerBus [2], which manages an event bus > and a > > > > > > > > > single-threaded event queue. > > > > > > > > > > > > > > > > > > - The API consists solely of methods that return void > without > > > > > checked > > > > > > > > > exceptions: IOW, the API wasn't designed to allow for > listeners > > > > to > > > > > > > > > interact with the server (other than throwing an unchecked > > > > > exception, > > > > > > > > > of course). > > > > > > > > > > > > > > > > > > - Afaict if a listener throws, the bus catches the > exception > > > and > > > > > moves > > > > > > > on. > > > > > > > > > > > > > > > > > > I'm not an expert in this topic so I might be wrong here, > but > > > the > > > > > > > > > suggestion that Spark event listeners were designed to > allow > > > > > listeners > > > > > > > > > to modify Spark's behavior doesn't look accurate to me. > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > Alex > > > > > > > > > > > > > > > > > > [1]: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://www.ibm.com/think/insights/apache-spark-monitoring-using-listeners-and-data-quality-libraries > > > > > > > > > [2]: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://spark.apache.org/docs/latest/api/java/org/apache/spark/scheduler/SparkListenerBus.html > > > > > > > > > > > > > > > > > > On Tue, Nov 11, 2025 at 1:30 PM Dmitri Bourlatchkov < > > > > > [email protected]> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > Hi Eric, > > > > > > > > > > > > > > > > > > > > I would very much prefer not to use the event listener > SPI > > > as a > > > > > > > means to > > > > > > > > > > control the operation of the Polaris Server. > > > > > > > > > > > > > > > > > > > > More specifically, I believe that any error / exception > in an > > > > > event > > > > > > > > > > listener should not affect the processing of the request. > > > > > > > > > > > > > > > > > > > > If we need custom callbacks to control some aspects of > the > > > > server > > > > > > > > > > behaviour, let's define a dedicated SPI for that, but, > IMHO, > > > it > > > > > > > should be > > > > > > > > > > outside the scope of events. WDYT? > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > Dmitri. > > > > > > > > > > > > > > > > > > > > On Mon, Nov 10, 2025 at 8:55 PM Eric Maynard < > > > > > > > [email protected]> > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > In fact, shouldn’t it be exclusively a listener’s > decision > > > on > > > > > > > whether > > > > > > > > > an > > > > > > > > > > > event is handled in a blocking way or not? As was > noted in > > > a > > > > > past > > > > > > > > > thread on > > > > > > > > > > > events, much of the utility of the event framework > comes > > > from > > > > > the > > > > > > > > > ability > > > > > > > > > > > to introduce custom logic and hooks into the normal > > > operation > > > > > of > > > > > > > > > Polaris. > > > > > > > > > > > > > > > > > > > > > > If you wish, for example, to prevent the creation of > more > > > > than > > > > > 1k > > > > > > > > > tables > > > > > > > > > > > with some given prefix, you can do so using a > listener. If > > > > the > > > > > > > event > > > > > > > > > which > > > > > > > > > > > might trigger that logic becomes non-blocking, you > would no > > > > > longer > > > > > > > be > > > > > > > > > able > > > > > > > > > > > to block/fail the create table request. > > > > > > > > > > > > > > > > > > > > > > I think maybe it’s the name “event”, but we seem to > keep > > > > > conflating > > > > > > > > > these > > > > > > > > > > > hooks with the iceberg events or auditing events when > they > > > > are > > > > > not > > > > > > > > > exactly > > > > > > > > > > > the same thing. > > > > > > > > > > > > > > > > > > > > > > —EM > > > > > > > > > > > > > > > > > > > > > > On Mon, Nov 10, 2025 at 8:47 PM Adnan Hemani > > > > > > > > > > > <[email protected]> wrote: > > > > > > > > > > > > > > > > > > > > > > > Hi Alex, > > > > > > > > > > > > > > > > > > > > > > > > Thanks for writing down the proposal for this! As I > had > > > > > > > previously > > > > > > > > > > > > suggested this when implementing the Persistence of > > > Polaris > > > > > > > Events > > > > > > > > > > > > <https://github.com/apache/polaris/pull/1844>, I am > > > > > obviously > > > > > > > very > > > > > > > > > much > > > > > > > > > > > in > > > > > > > > > > > > favor of doing this :) > > > > > > > > > > > > > > > > > > > > > > > > A few questions I have regarding your vision of how > we > > > > should > > > > > > > > > implement > > > > > > > > > > > > this: > > > > > > > > > > > > * Are you envisioning anything for being able to make > > > > > > > dependencies > > > > > > > > > > > between > > > > > > > > > > > > event listeners? Or are we taking a set direction > that > > > > Event > > > > > > > > > Listeners > > > > > > > > > > > > should be independent of each other? > > > > > > > > > > > > * In some listeners we have the ability to make > events > > > > > emission > > > > > > > > > > > synchronous > > > > > > > > > > > > [example > > > > > > > > > > > > < > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://github.com/apache/polaris/blob/main/runtime/service/src/main/java/org/apache/polaris/service/events/jsonEventListener/aws/cloudwatch/AwsCloudWatchEventListener.java#L186 > > > > > > > > > > > > >]. > > > > > > > > > > > > How do we plan to support/advise (or not...) that > with > > > the > > > > > > > > > introduction > > > > > > > > > > > > of @Blocking annotations. > > > > > > > > > > > > > > > > > > > > > > > > Best, > > > > > > > > > > > > Adnan Hemani > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Nov 10, 2025 at 11:29 AM Yufei Gu < > > > > > [email protected]> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > Thanks for the reply. It's overall a good idea to > have > > > > > async > > > > > > > event > > > > > > > > > > > > > listeners so that they are not blocking each other. > > > > > > > > > > > > > > > > > > > > > > > > > > One downside of the async ones is that event order > > > isn't > > > > > > > > > deterministic. > > > > > > > > > > > > > For example, event listeners of Spark need the > order to > > > > > > > understand > > > > > > > > > the > > > > > > > > > > > > > execution semantics. I think Polaris is fine with > that, > > > > > given > > > > > > > the > > > > > > > > > ts of > > > > > > > > > > > > > each event is generated by Polaris. The downstream > can > > > > > still > > > > > > > > > figure out > > > > > > > > > > > > the > > > > > > > > > > > > > order. > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks Pierre for sharing, I think any I/O-bound or > > > > > potentially > > > > > > > > > slow > > > > > > > > > > > > > listener should be annotated with @Blocking. That > > > ensures > > > > > we > > > > > > > keep > > > > > > > > > the > > > > > > > > > > > > event > > > > > > > > > > > > > loop responsive and avoid impacting REST latency. > > > > > > > > > > > > > > > > > > > > > > > > > > Yufei > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Nov 10, 2025 at 9:43 AM Alexandre Dutra < > > > > > > > [email protected] > > > > > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi all, > > > > > > > > > > > > > > > > > > > > > > > > > > > > Answering the questions above: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > However, we can easily make sure that we use > > > > Quarkus's > > > > > > > SmallRye > > > > > > > > > > > Fault > > > > > > > > > > > > > > Tolerance > > > > > > > > > > > > > > > > > > > > > > > > > > > > Yes, that was my idea. It's not so much the bus > > > itself > > > > > that > > > > > > > > > needs to > > > > > > > > > > > > > > be fault tolerant, but the receiving end, that > is, > > > the > > > > > > > > > listeners. A > > > > > > > > > > > > > > listener can fail for a variety of reasons (e.g. > > > remote > > > > > > > broker > > > > > > > > > > > > > > unavailable), it would be nice to be able to > backoff > > > > and > > > > > > > retry > > > > > > > > > > > > > > automatically. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Since the Vert.x event bus runs on event-loop > > > threads > > > > > [...] > > > > > > > > > could > > > > > > > > > > > > > > blocking or slow event listeners potentially > stall > > > REST > > > > > > > requests > > > > > > > > > and > > > > > > > > > > > > > impact > > > > > > > > > > > > > > latency? > > > > > > > > > > > > > > > > > > > > > > > > > > > > What Pierre said: this could indeed happen, but > it's > > > > > > > possible to > > > > > > > > > > > > > > annotate the receiving end with @Blocking, in > which > > > > > case, the > > > > > > > > > > > listener > > > > > > > > > > > > > > will be invoked in a separate pool. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > With asynchronous event listeners, is there a > > > > > guarantee of > > > > > > > > > delivery > > > > > > > > > > > > to > > > > > > > > > > > > > > all listeners for a given event? > > > > > > > > > > > > > > > > > > > > > > > > > > > > If I understand the question correctly: with > > > > asynchronous > > > > > > > > > delivery, a > > > > > > > > > > > > > > slow or failing listener wouldn't impact the > delivery > > > > of > > > > > the > > > > > > > same > > > > > > > > > > > > > > event to other listeners. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > Alex > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Nov 10, 2025 at 10:12 AM Pierre Laporte < > > > > > > > > > > > [email protected] > > > > > > > > > > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks for the proposal, Alex. This sounds > like a > > > > > great > > > > > > > > > > > improvement. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > @Yufei As per Quarkus documentation, slow event > > > > > listeners > > > > > > > > > should be > > > > > > > > > > > > > > marked > > > > > > > > > > > > > > > with @Blocking so that they are not run on the > > > event > > > > > loop > > > > > > > > > threads. > > > > > > > > > > > > > > > -- > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Pierre > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Sat, Nov 8, 2025 at 2:14 AM Michael Collado > < > > > > > > > > > > > > [email protected] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > With asynchronous event listeners, is there a > > > > > guarantee > > > > > > > of > > > > > > > > > > > delivery > > > > > > > > > > > > > to > > > > > > > > > > > > > > all > > > > > > > > > > > > > > > > listeners for a given event? The downside of > > > > > synchronous > > > > > > > > > > > listeners > > > > > > > > > > > > is > > > > > > > > > > > > > > that > > > > > > > > > > > > > > > > everything is serial, but also if something > > > fails, > > > > > > > processing > > > > > > > > > > > > stops. > > > > > > > > > > > > > > This > > > > > > > > > > > > > > > > feels important for auditing purposes, though > > > less > > > > > > > important > > > > > > > > > for > > > > > > > > > > > > > other > > > > > > > > > > > > > > > > cases. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Mike > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Nov 7, 2025 at 2:28 PM Yufei Gu < > > > > > > > > > [email protected]> > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, Alex and Adam. One concern I have > is > > > > about > > > > > the > > > > > > > > > shared > > > > > > > > > > > > > runtime > > > > > > > > > > > > > > > > > thread pool. > > > > > > > > > > > > > > > > > Since the Vert.x event bus runs on > event-loop > > > > > threads > > > > > > > that > > > > > > > > > are > > > > > > > > > > > > also > > > > > > > > > > > > > > used > > > > > > > > > > > > > > > > by > > > > > > > > > > > > > > > > > Quarkus’ reactive REST endpoints, could > > > blocking > > > > or > > > > > > > slow > > > > > > > > > event > > > > > > > > > > > > > > listeners > > > > > > > > > > > > > > > > > potentially stall REST requests and impact > > > > latency? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Yufei > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Nov 7, 2025 at 11:25 AM Adam > Christian > > > < > > > > > > > > > > > > > > > > > [email protected]> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I think that this would be a great > > > enhancement. > > > > > > > Thanks > > > > > > > > > for > > > > > > > > > > > > > > proposing > > > > > > > > > > > > > > > > it! > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The only concern I would have is around > > > > > > > fault-tolerance. > > > > > > > > > From > > > > > > > > > > > > > what > > > > > > > > > > > > > > I > > > > > > > > > > > > > > > > can > > > > > > > > > > > > > > > > > > tell, from the Quarkus documentation, the > > > > Quarkus > > > > > > > event > > > > > > > > > bus > > > > > > > > > > > > uses > > > > > > > > > > > > > > Vert.x > > > > > > > > > > > > > > > > > > EventBus which does not guarantee message > > > > > delivery if > > > > > > > > > failure > > > > > > > > > > > > of > > > > > > > > > > > > > > part > > > > > > > > > > > > > > > > of > > > > > > > > > > > > > > > > > > the event bus occurs [1]. However, we can > > > > easily > > > > > make > > > > > > > > > sure > > > > > > > > > > > that > > > > > > > > > > > > > we > > > > > > > > > > > > > > use > > > > > > > > > > > > > > > > > > Quarkus's SmallRye Fault Tolerance [2]. > Is my > > > > > rough > > > > > > > > > > > > understanding > > > > > > > > > > > > > > > > inline > > > > > > > > > > > > > > > > > > with your proposal? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Go community, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Adam > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > [1]: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://vertx.io/docs/apidocs/io/vertx/core/eventbus/EventBus.html > > > > > > > > > > > > > > > > > > [2]: > > > > > > > https://quarkus.io/guides/smallrye-fault-tolerance > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Nov 7, 2025 at 11:49 AM Alexandre > > > > Dutra < > > > > > > > > > > > > > [email protected] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi all, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I'd like to propose an enhancement to > our > > > > > existing > > > > > > > > > events > > > > > > > > > > > > > > feature: > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > > > > ability to support multiple listeners. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Currently, only a single listener can > be > > > > > active at > > > > > > > a > > > > > > > > > time, > > > > > > > > > > > > > which > > > > > > > > > > > > > > is > > > > > > > > > > > > > > > > > > > quite limiting. For example, we might > need > > > to > > > > > > > persist > > > > > > > > > > > events > > > > > > > > > > > > > for > > > > > > > > > > > > > > > > audit > > > > > > > > > > > > > > > > > > > purposes and simultaneously send them > to a > > > > > message > > > > > > > > > queue > > > > > > > > > > > for > > > > > > > > > > > > > > > > > > > optimization. With the current setup, > this > > > > > isn't > > > > > > > easily > > > > > > > > > > > > > > achievable. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > While a composite listener could be > > > created, > > > > it > > > > > > > feels > > > > > > > > > like > > > > > > > > > > > a > > > > > > > > > > > > > less > > > > > > > > > > > > > > > > > > > elegant solution, and the delivery > would be > > > > > > > strictly > > > > > > > > > > > serial, > > > > > > > > > > > > > > > > > > > processing one listener after another. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > My suggestion is to leverage Quarkus > > > internal > > > > > > > event bus > > > > > > > > > > > [1]: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 1) There will be one central event > emitter > > > > > > > responsible > > > > > > > > > for > > > > > > > > > > > > > > publishing > > > > > > > > > > > > > > > > > > > events to the bus. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 2) We will have zero to N listeners, > each > > > > > > > independently > > > > > > > > > > > > > watching > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > > > > event bus for relevant events. They > will be > > > > > > > discovered > > > > > > > > > by > > > > > > > > > > > > CDI. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 3) We could apply filters to each > listener, > > > > > e.g. > > > > > > > > > listener A > > > > > > > > > > > > > > listens > > > > > > > > > > > > > > > > > > > for event types X and Y, listener B > only > > > > > listens to > > > > > > > > > event > > > > > > > > > > > > type > > > > > > > > > > > > > Y. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 4) This approach would ensure fully > > > > > asynchronous > > > > > > > > > delivery > > > > > > > > > > > of > > > > > > > > > > > > > > events > > > > > > > > > > > > > > > > to > > > > > > > > > > > > > > > > > > > all interested listeners. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 5) Fault-tolerance could also be easily > > > > > implemented > > > > > > > > > (event > > > > > > > > > > > > > > delivery > > > > > > > > > > > > > > > > > > > retries, timeouts, etc.). > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > What do you all think? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > > Alex > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > [1]: > > > > > https://quarkus.io/guides/reactive-event-bus > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
