> > We guarantee that the metadata of the dead stream threads will be > returned by KafkaStreams#localThreadsMetadata() at least until the next > call to KafkaStreams#addStreamThread() or > KafkaStreams#removeStreamThread() after the stream thread transited to > DEAD
This seems kind of tricky...personally I would find it pretty odd if I queried the local thread metadata and found two threads, A (alive) and B (dead), and then called removeStreamThread() and now suddenly I have zero. Or if I call addStreamThread and now I still have two threads. Both of those results seem to indicate that only live threads "count" and are returned by localThreadsMetadata(). But in reality we do temporarily keep the dead thread, but only for the arbitrary amount of time until the next time you want to add or remove some other stream thread? That seems like a weird side effect of the add/removeStreamThread APIs. If we really think users might want to log the metadata of dead threads, then let's just do that for them or give them a way to do exactly that. I'm not that concerned about the backwards compatibility of removing dead threads from the localThreadsMetadata, because I find it hard to believe that users do anything other than just skip over them in the list (set?) that gets returned. But maybe someone can chime in with an example use case. I'm actually even a little skeptical that any users might want to log the metadata of a dead thread, since all of the metadata is only useful for IQ on live threads or already covered by other easily discoverable logging elsewhere, or both. On Wed, Sep 16, 2020 at 2:07 AM Bruno Cadonna <br...@confluent.io> wrote: > Hi again, > > I just realized that if we filter out DEAD stream threads in > localThreadsMetadata(), users cannot log the metadata of dying stream > threads in the uncaught exception handler. > > I realized this thanks to the example Guozhang requested in the KIP. > Thank you for that, Guozhang! > > Hence, I adapted the KIP as follows: > > - We do not filter out DEAD stream threads in > KafkaStreams#localThreadsMetadata() > > - We guarantee that the metadata of the dead stream threads will be > returned by KafkaStreams#localThreadsMetadata() at least until the next > call to KafkaStreams#addStreamThread() or > KafkaStreams#removeStreamThread() after the stream thread transited to > DEAD. Besides giving users the opportunity to log the metadata of a > dying stream thread in its uncaught exception handler, this guarantee > makes KafkaStreams#localThreadsMetadata() completely backward compatible > to the current behavior, because if KafkaStreams#addStreamThread() and > KafkaStreams#removeStreamThread() are never called, > KafkaStreams#localThreadsMetadata() will also return the metadata of all > streams threads that have ever died which corresponds to the current > behavior. > > - We guarantee that dead stream threads are removed from a Kafka Streams > client at latest after the next call to KafkaStreams#addStreamThread() > or KafkaStreams#removeStreamThread() following the transition of the > stream thread to DEAD. This guarantees that the number of maintained > stream threads does not grow indefinitely. > > > Best, > Bruno > > > > On 16.09.20 09:23, Bruno Cadonna wrote: > > Hi Guozhang, > > > > Good point! I would propose to filter out DEAD stream threads in > > localThreadsMetadata() to get consistent results that do not depend on > > timing. I will update the KIP accordingly. > > > > Best, > > Bruno > > > > On 16.09.20 06:02, Guozhang Wang wrote: > >> Thanks Bruno, your replies make sense to me. As for > >> localThreadsMetadata() itself, > >> I'd like to clarify if it would return any still-bookkept threads, or > >> would > >> it specifically filter out those DEAD threads even if they are not yet > >> removed. > >> > >> Otherwise, the KIP LGTM. > >> > >> Guozhang > >> > >> On Tue, Sep 15, 2020 at 2:58 AM Bruno Cadonna <br...@confluent.io> > wrote: > >> > >>> Hi Guozhang, > >>> > >>> Thank you for your feedback. I replied inline. > >>> > >>> Best, > >>> Bruno > >>> > >>> On 09.09.20 23:43, Guozhang Wang wrote: > >>>> Hello Bruno, > >>>> > >>>> Finally got some time to review your KIP and the discussion thread > >>>> now.. > >>> a > >>>> few comments below: > >>>> > >>>> 1) I'm with Matthias about the newly added numberOfAliveStreamThreads > >>> v.s. > >>>> existing localThreadsMetadata: to me it seems we can always achieve > the > >>>> first based on the second. It seems not worthy to provide some "syntax > >>>> sugar" to the API but just let users do the filtering themselves. > >>> > >>> I am not married to that method. I removed it. > >>> > >>>> Furthermore, I'm wondering what's the rationale behind removing the > >>>> DEAD > >>>> threads from localThreadsMetadata()? Personally I feel returning all > >>>> threads, including those who are ever closed, either due to > >>>> exception or > >>>> due to removeStreamThread, would be beneficial for debugging > >>>> purposes, as > >>>> long as within the lifetime of an instance we expect the amount of > such > >>>> dead threads will not increase linearly --- and if we agree with that, > >>>> maybe we can rename "removeStreamThread" to sth. like > >>>> "terminateStreamThread" indicating it is only terminated but not > >>>> removed > >>>> --- and of course if users do not want to see those DEAD threads > >>>> they can > >>>> always filter them out. I'm just proposing that we should still > >>>> leave the > >>>> door open for those who want to check those ever terminated threads. > >>>> > >>> > >>> I actually think the number of dead stream threads might increase > >>> linearly. Assume users have a systematic error that continuously kills > a > >>> stream thread and they blindly start a new stream thread in the > uncaught > >>> exception handler. This scenario might be a mistake but if the > >>> systematic error does not occur at a high rate, it could also be a > >>> strategy to keep the application running during the investigation of > the > >>> systematic error. > >>> > >>> IMO, removing dead stream threads makes Kafka Streams more robust > >>> because it prevent a possibly unbounded increase of memory usage. If > >>> users want to debug the dead stream threads they can monitor the number > >>> of dead threads with the metric proposed in the KIP and they could > >>> additionally log the metadata of the dying stream thread in the > uncaught > >>> exception handler. I do not think that there is need to keep dead > stream > >>> threads around. > >>> > >>>> 2) I think it would help to write down some example user code in > >>> exception > >>>> handler e.g. to illustrate how this would be implemented -- e.g. we > >>>> know > >>>> that practically the handler need to maintain a "this" reference of > the > >>>> instance anyways in order to shutdown the whole instance or, > >>> add/terminate > >>>> threads dynamically, but I want to see if we have listed all possible > >>> call > >>>> paths like: a) a thread's handler logic to terminate another thread, > >>>> b) a > >>>> thread handler to add new threads, etc are all appropriately supported > >>>> without deadlocks. > >>>> > >>> > >>> I added an example for an uncaught exception handler that adds a stream > >>> thread to the KIP. Removing a stream thread in an uncaught exception > >>> handler doesn't seem a common use case to me. Nevertheless, we need to > >>> make sure that we do not run in a deadlock in that case. I will > consider > >>> that during the implementation and write tests to check for deadlocks. > >>> > >>> Shutting down the Kafka Streams client from inside an uncaught > exception > >>> handler is outside the scope of this KIP. In the beginning it was part > >>> of the KIP, but during the discussion it turned out that we can fix our > >>> existing close() method to accomplish the shutdown from inside an > >>> uncaught exception handler. But I completely agree with you that we > need > >>> to ensure that we do not run into a deadlock in this case. > >>> > >>> > >>>> > >>>> Guozhang > >>>> > >>>> > >>>> On Wed, Sep 9, 2020 at 11:35 AM Matthias J. Sax <mj...@apache.org> > >>> wrote: > >>>> > >>>>> I would prefer to not add a new method. It seems unnecessary. > >>>>> `localThreadMetadata` does return all threads in all states(*) and > >>>>> thus > >>>>> provides full insight. > >>>>> > >>>>> (*) A thread in state DEAD could be returned as long as it's not > >>>>> removed > >>>>> yet. > >>>>> > >>>>> I don't see any advantage to pre-filter threads and to exclude > threads > >>>>> in state CREATE or PENDING_SHUTDOWN. Even if a CREATED thread is not > >>>>> started yet, it is still "alive" in a broader sense. For example, if > a > >>>>> user wants to scale out to 10 thread, and 8 are RUNNING and 2 are in > >>>>> state CREATED, a user won't need to add 2 more threads -- there are > >>>>> already 10 threads. > >>>>> > >>>>> For PENDING_SHUTDOWN and scale in it would be different I guess, as > >>>>> the > >>>>> proposal would be to filter them out right away. However, filtering > >>>>> them > >>>>> seems actually not to be "correct", as a thread in PENDING_SHUTDOWN > >>>>> might still process data and it's thus still "alive". > >>>>> > >>>>> If there is still a need later to add a new method about "alive > >>>>> thread" > >>>>> we can always add as a follow up -- removing things is much harder. > >>>>> > >>>>> I also don't think that there is value in returning names of dead > >>>>> threads, as we recycle names. > >>>>> > >>>>> > >>>>> -Matthias > >>>>> > >>>>> > >>>>> On 9/9/20 10:04 AM, Sophie Blee-Goldman wrote: > >>>>>> I agree that the current behavior of localThreadsMetadata() does not > >>> seem > >>>>>> to match, but it seems like we will be forced to change it to only > >>> return > >>>>>> currently-alive threads. For one thing, we plan to recycle old > thread > >>>>> names. > >>>>>> It would be pretty confusing for a user to get two (or more) > >>>>> ThreadMetadata > >>>>>> objects returned with the same name, since AFAICT this is the only > >>>>>> distinguishing identifier of stream threads. I think we should > >>>>>> enforce > >>>>> that > >>>>>> only live threads are returned by localThreadsMetadata(). Plus, as > >>>>> Matthias > >>>>>> pointed out, we plan to remove dead threads from the KafkaStreams > >>> client, > >>>>>> so still returning them in the metadata would be extremely odd. > >>>>>> > >>>>>> If we think that there might be some use case that requires knowing > >>> which > >>>>>> threads have died, we could consider adding a method that returns > the > >>>>>> names of dead threads. But the only use case I can imagine would > >>> probably > >>>>>> be better served by a callback that gets invoked when the thread > >>>>>> dies, > >>>>> which > >>>>>> we already have. > >>>>>> > >>>>>> On Tue, Sep 8, 2020 at 11:46 PM Bruno Cadonna <br...@confluent.io> > >>>>> wrote: > >>>>>> > >>>>>>> Hi Matthias and Sophie, > >>>>>>> > >>>>>>> I agree that localThreadsMetadata() can be used here. However, > >>>>>>> localThreadsMetadata() returns all stream threads irrespectively of > >>>>>>> their states. Alive stream threads are specified as being in one of > >>> the > >>>>>>> following states: RUNNING, STARTING, PARTITIONS_REVOKED, and > >>>>>>> PARTITIONS_ASSIGNED. Hence, users would need to filter the result > of > >>>>>>> localThreadsMetadata(). I thought, it would be neat to have a > method > >>>>>>> that hides this filtering and returns the number of alive stream > >>>>>>> threads, because that is the most basic information you might > >>>>>>> need to > >>>>>>> decide about adding or removing stream threads. For all more > >>>>>>> advanced > >>>>>>> use cases users should use localThreadsMetadata(). I am also happy > >>> with > >>>>>>> removing the method. WDYT? > >>>>>>> > >>>>>>> Best, > >>>>>>> Bruno > >>>>>>> > >>>>>>> On 09.09.20 03:51, Matthias J. Sax wrote: > >>>>>>>> Currently we, don't cleanup dead threads, but the KIP proposes to > >>>>> change > >>>>>>>> this: > >>>>>>>> > >>>>>>>>> Stream threads that are in state DEAD will be removed from the > >>> stream > >>>>>>> threads of a Kafka Streams client. > >>>>>>>> > >>>>>>>> > >>>>>>>> -Matthias > >>>>>>>> > >>>>>>>> On 9/8/20 2:37 PM, Sophie Blee-Goldman wrote: > >>>>>>>>> Ah, I forgot about localThreadsMetadata(). In that. case I agree, > >>>>>>> there's > >>>>>>>>> no reason > >>>>>>>>> to introduce a new method when we can get both the names and > >>>>>>>>> number > >>> of > >>>>>>> all > >>>>>>>>> running threads from this. > >>>>>>>>> > >>>>>>>>> I assume that we would update localThreadsMetadata to only return > >>>>>>> currently > >>>>>>>>> alive threads as part of this KIP -- at a quick glance, it seems > >>> like > >>>>> we > >>>>>>>>> don't do > >>>>>>>>> any pruning of dead threads at the moment > >>>>>>>>> > >>>>>>>>> On Tue, Sep 8, 2020 at 1:58 PM Matthias J. Sax <mj...@apache.org > > > >>>>>>> wrote: > >>>>>>>>> > >>>>>>>>>> I am not sure if we need a new method? There is already > >>>>>>>>>> `localThreadsMetadata()`. What do we gain by adding a new one? > >>>>>>>>>> > >>>>>>>>>> Returning the thread's name (as `Optional<String>`) for both > >>>>>>>>>> add() > >>>>> and > >>>>>>>>>> remove() is fine with me. > >>>>>>>>>> > >>>>>>>>>> > >>>>>>>>>> -Matthias > >>>>>>>>>> > >>>>>>>>>> On 9/8/20 12:58 PM, Sophie Blee-Goldman wrote: > >>>>>>>>>>> Sorry Bruno, I think I missed the end of your message with the > >>>>>>>>>>> numberOfAliveStreamThreads() > >>>>>>>>>>> proposal. I agree, that would be better than the alternatives I > >>>>>>> listed. > >>>>>>>>>>> That said: > >>>>>>>>>>> > >>>>>>>>>>>> They rather suggest that the method returns a list of > >>>>>>>>>>>> handles to > >>>>> the > >>>>>>>>>>> stream threads. > >>>>>>>>>>> > >>>>>>>>>>> I hadn't thought of that originally, but now that you mention > >>>>>>>>>>> it, > >>>>> this > >>>>>>>>>>> might be a good idea. > >>>>>>>>>>> I don't think we should return actual handles on the threads, > >>>>>>>>>>> but > >>>>>>> maybe a > >>>>>>>>>>> list of the thread > >>>>>>>>>>> names rather than a single number of currently alive threads. > >>>>>>>>>>> > >>>>>>>>>>> Since we seem to think it would be difficult if not > >>>>>>>>>>> impossible to > >>>>> keep > >>>>>>>>>>> track of the number > >>>>>>>>>>> of running stream threads, we should apply the same reasoning > to > >>> the > >>>>>>>>>> names > >>>>>>>>>>> and not > >>>>>>>>>>> assume the user can/will keep track of every thread returned by > >>>>>>>>>>> addStreamThread() or > >>>>>>>>>>> removeStreamThread(). Users should generally take any required > >>>>> action > >>>>>>>>>>> immediately > >>>>>>>>>>> after adding/removing the thread -- eg deregistering the thread > >>>>>>> metrics > >>>>>>>>>> -- > >>>>>>>>>>> but it might > >>>>>>>>>>> still be useful to provide a convenience method listing all > >>>>>>>>>>> of the > >>>>>>>>>> current > >>>>>>>>>>> threads > >>>>>>>>>>> > >>>>>>>>>>> And of course you could still get the number of threads > >>>>>>>>>>> easily by > >>>>>>>>>> invoking > >>>>>>>>>>> size() on the > >>>>>>>>>>> returned list (or ordered set?). > >>>>>>>>>>> > >>>>>>>>>>> On Tue, Sep 8, 2020 at 12:16 PM Bruno Cadonna > >>>>>>>>>>> <br...@confluent.io > >>>> > >>>>>>>>>> wrote: > >>>>>>>>>>> > >>>>>>>>>>>> Thank you again for the feedback Sophie! > >>>>>>>>>>>> > >>>>>>>>>>>> As I tried to point out in my previous e-mail, removing a > >>>>>>>>>>>> stream > >>>>>>> thread > >>>>>>>>>>>> from a Kafka Streams client that does not have alive stream > >>> threads > >>>>>>> is > >>>>>>>>>>>> nothing exceptional for the client per se. However, it can > >>>>>>>>>>>> become > >>>>>>>>>>>> exceptional within the context of the user. For example, if > >>>>>>>>>>>> users > >>>>>>> want > >>>>>>>>>>>> to remove a stream thread from a client without alive stream > >>>>> threads > >>>>>>>>>>>> because one if their metrics say so, then this is > >>>>>>>>>>>> exceptional in > >>>>> the > >>>>>>>>>>>> context of that user metric not in the context of the Kafka > >>> Streams > >>>>>>>>>>>> client. In that case, users should throw an exception and > >>>>>>>>>>>> handle > >>>>> it. > >>>>>>>>>>>> > >>>>>>>>>>>> Regarding returning null, I do not like to return null because > >>>>> from a > >>>>>>>>>>>> development point of view there is no distinction between > >>> returning > >>>>>>> null > >>>>>>>>>>>> because we have a bug in the code or returning null because > >>>>>>>>>>>> there > >>>>>>> are no > >>>>>>>>>>>> alive stream threads. Additionally, Optional<String> makes it > >>> more > >>>>>>>>>>>> explicit that the result could also be empty. > >>>>>>>>>>>> > >>>>>>>>>>>> Thank you for the alternative method names! However, with the > >>> names > >>>>>>> you > >>>>>>>>>>>> propose it is not immediately clear that the method returns an > >>>>>>> amount of > >>>>>>>>>>>> stream threads. They rather suggest that the method returns a > >>> list > >>>>> of > >>>>>>>>>>>> handles to the stream threads. I chose to use > >>> "aliveStreamThreads" > >>>>>>> to be > >>>>>>>>>>>> consistent with the client-level metric "alive-stream-threads" > >>>>> which > >>>>>>>>>>>> reports the same number of stream threads that > >>>>>>>>>>>> numberOfAliveStreamThreads() should report. If others also > >>>>>>>>>>>> think > >>>>> that > >>>>>>>>>>>> the proposed name in the KIP is too clumsy, I am open to > rename > >>> it, > >>>>>>>>>> though. > >>>>>>>>>>>> > >>>>>>>>>>>> Best, > >>>>>>>>>>>> Bruno > >>>>>>>>>>>> > >>>>>>>>>>>> > >>>>>>>>>>>> On 08.09.20 20:12, Sophie Blee-Goldman wrote: > >>>>>>>>>>>>>> it's never a good sign when the discussion moves into the > >>>>>>>>>>>>>> vote > >>>>>>> thread > >>>>>>>>>>>>> > >>>>>>>>>>>>> Hah, sorry, the gmail consolidation of [VOTE] and [DISCUSS] > >>>>> threads > >>>>>>>>>>>> strikes > >>>>>>>>>>>>> again. > >>>>>>>>>>>>> Thanks for redirecting me Bruno > >>>>>>>>>>>>> > >>>>>>>>>>>>> I suppose it's unfair to expect the callers to keep perfect > >>> track > >>>>> of > >>>>>>>>>> the > >>>>>>>>>>>>> current > >>>>>>>>>>>>> number of stream threads, but it also seems like you > >>> shouldn't > >>>>> be > >>>>>>>>>>>> calling > >>>>>>>>>>>>> removeStreamThread() when there are no threads left. Either > >>> you're > >>>>>>> just > >>>>>>>>>>>>> haphazardly removing threads and could unintentionally slip > >>> into a > >>>>>>>>>> state > >>>>>>>>>>>> of > >>>>>>>>>>>>> no > >>>>>>>>>>>>> running threads without realizing it, or more realistically, > >>>>> you're > >>>>>>>>>>>>> carefully > >>>>>>>>>>>>> removing threads based on some metric(s) that convey > >>>>>>>>>>>>> whether the > >>>>>>> system > >>>>>>>>>>>> is > >>>>>>>>>>>>> over or under-provisioned. If your metrics say you're > >>>>>>> over-provisioned > >>>>>>>>>>>> but > >>>>>>>>>>>>> there's > >>>>>>>>>>>>> not one thread running, well, that certainly sounds > >>>>>>>>>>>>> exceptional > >>> to > >>>>>>> me. > >>>>>>>>>> Or > >>>>>>>>>>>>> you might > >>>>>>>>>>>>> be right in that the cluster is over-provisioned but have > just > >>>>> been > >>>>>>>>>>>>> directing the > >>>>>>>>>>>>> removeStreamThread() and addStreamThread() calls to > >>>>>>>>>>>>> instances at > >>>>>>>>>> random, > >>>>>>>>>>>> and > >>>>>>>>>>>>> end up with one massive instance and one with no threads at > >>>>>>>>>>>>> all. > >>>>>>> Again, > >>>>>>>>>>>>> this > >>>>>>>>>>>>> probably merits some human intervention (or system redesign) > >>>>>>>>>>>>> > >>>>>>>>>>>>> That said, I don't think there's any real harm to just > >>>>>>>>>>>>> returning > >>>>>>> null > >>>>>>>>>> in > >>>>>>>>>>>>> this case, but I hope > >>>>>>>>>>>>> that users would pay attention to this since it seems > >>>>>>>>>>>>> likely to > >>>>>>>>>> indicate > >>>>>>>>>>>>> something has gone > >>>>>>>>>>>>> seriously wrong. I suppose Optional<String> would be a > >>> reasonable > >>>>>>>>>>>>> compromise. > >>>>>>>>>>>>> > >>>>>>>>>>>>> As for the method name, what about activeStreamThreads() or > >>>>>>>>>>>>> liveStreamThreads() ? > >>>>>>>>>>>>> > >>>>>>>>>>>>> On Mon, Sep 7, 2020 at 1:45 AM Bruno Cadonna < > >>> br...@confluent.io> > >>>>>>>>>> wrote: > >>>>>>>>>>>>> > >>>>>>>>>>>>>> Hi John, > >>>>>>>>>>>>>> > >>>>>>>>>>>>>> I agree with you except for checking null. I would rather > >>> prefer > >>>>> to > >>>>>>>>>> use > >>>>>>>>>>>>>> Optional<String> as the return type to both methods. > >>>>>>>>>>>>>> > >>>>>>>>>>>>>> I changed the subject from [VOTE] to [DISCUSS] so that we > can > >>>>>>> follow > >>>>>>>>>> up > >>>>>>>>>>>>>> in the discussion thread. > >>>>>>>>>>>>>> > >>>>>>>>>>>>>> Best, > >>>>>>>>>>>>>> Bruno > >>>>>>>>>>>>>> > >>>>>>>>>>>>>> On 04.09.20 23:12, John Roesler wrote: > >>>>>>>>>>>>>>> Hi Sophie, > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> Uh, oh, it's never a good sign when the discussion moves > >>>>>>>>>>>>>>> into the vote thread :) > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> I agree with you, it seems like a good touch for > >>>>>>>>>>>>>>> removeStreamThread() to return the name of the thread that > >>>>>>>>>>>>>>> got removed, rather than a boolean flag. Maybe the return > >>>>>>>>>>>>>>> value would be `null` if there is no thread to remove. > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> If we go that way, I'd suggest that addStreamThread() also > >>>>>>>>>>>>>>> return the name of the newly created thread, or null if no > >>>>>>>>>>>>>>> thread can be created right now. > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> I'm not completely sure if I think that callers of this > >>>>>>>>>>>>>>> method would know exactly how many threads there are. Sure, > >>>>>>>>>>>>>>> if a human being is sitting there looking at the metrics or > >>>>>>>>>>>>>>> logs and decides to call the method, it would work out, but > >>>>>>>>>>>>>>> I'd expect this kind of method to find its way into > >>>>>>>>>>>>>>> automated tooling that reacts to things like current system > >>>>>>>>>>>>>>> load or resource saturation. Those kinds of toolchains > often > >>>>>>>>>>>>>>> are part of a distributed system, and it's probably not > that > >>>>>>>>>>>>>>> easy to guarantee that the thread count they observe is > >>>>>>>>>>>>>>> fully consistent with the number of threads that are > >>>>>>>>>>>>>>> actually running. Therefore, an in-situ `int > >>>>>>>>>>>>>>> numStreamThreads()` method might not be a bad idea. Then > >>>>>>>>>>>>>>> again, it seems sort of optional. A caller can catch an > >>>>>>>>>>>>>>> exception or react to a `null` return value just the same > >>>>>>>>>>>>>>> either way. Having both add/remove methods behave similarly > >>>>>>>>>>>>>>> is probably more valuable. > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> Thanks, > >>>>>>>>>>>>>>> -John > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>>> On Thu, 2020-09-03 at 12:15 -0700, Sophie Blee-Goldman > >>>>>>>>>>>>>>> wrote: > >>>>>>>>>>>>>>>> Hey, sorry for the late reply, I just have one minor > >>>>> suggestion. > >>>>>>>>>> Since > >>>>>>>>>>>>>> we > >>>>>>>>>>>>>>>> don't > >>>>>>>>>>>>>>>> make any guarantees about which thread gets removed or > >>>>>>>>>>>>>>>> allow > >>>>> the > >>>>>>>>>> user > >>>>>>>>>>>> to > >>>>>>>>>>>>>>>> specify, I think we should return either the index or full > >>> name > >>>>>>> of > >>>>>>>>>> the > >>>>>>>>>>>>>>>> thread > >>>>>>>>>>>>>>>> that does get removed by removeThread(). > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>> I know you just updated the KIP to return true/false if > >>>>>>>>>>>>>>>> there > >>>>>>>>>>>>>> are/aren't any > >>>>>>>>>>>>>>>> threads to be removed, but I think this would be more > >>>>>>> appropriate as > >>>>>>>>>>>> an > >>>>>>>>>>>>>>>> exception than as a return type. I think it's reasonable > to > >>>>>>> expect > >>>>>>>>>>>>>> users to > >>>>>>>>>>>>>>>> have some sense to how many threads are remaining, and not > >>> try > >>>>> to > >>>>>>>>>>>> remove > >>>>>>>>>>>>>>>> a thread when there is none left. To me, that indicates > >>>>> something > >>>>>>>>>>>> wrong > >>>>>>>>>>>>>>>> with the user application code and should be treated as an > >>>>>>>>>> exceptional > >>>>>>>>>>>>>> case. > >>>>>>>>>>>>>>>> I don't think the same code clarify argument applies > >>>>>>>>>>>>>>>> here as > >>> to > >>>>>>> the > >>>>>>>>>>>>>>>> addStreamThread() case, as there's no reason for an > >>> application > >>>>>>> to > >>>>>>>>>> be > >>>>>>>>>>>>>>>> looping and retrying removeStreamThread() since if that > >>> fails, > >>>>>>> it's > >>>>>>>>>>>>>> because > >>>>>>>>>>>>>>>> there are no threads left and thus it will continue to > >>>>>>>>>>>>>>>> always > >>>>>>> fail. > >>>>>>>>>>>> And > >>>>>>>>>>>>>> if > >>>>>>>>>>>>>>>> the > >>>>>>>>>>>>>>>> user actually wants to shut down all threads, they should > >>> just > >>>>>>> close > >>>>>>>>>>>> the > >>>>>>>>>>>>>>>> whole application rather than call removeStreamThread() > >>>>>>>>>>>>>>>> in a > >>>>>>> loop. > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>> While I generally think it should be straightforward for > >>> users > >>>>> to > >>>>>>>>>>>> track > >>>>>>>>>>>>>> how > >>>>>>>>>>>>>>>> many stream threads they have running, maybe it would be > >>>>>>>>>>>>>>>> nice > >>>>> to > >>>>>>> add > >>>>>>>>>>>>>>>> a small utility method that does this for them. Something > >>> like > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>> // Returns the number of currently alive threads > >>>>>>>>>>>>>>>> boolean runningStreamThreads(); > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>> On Thu, Sep 3, 2020 at 7:41 AM Matthias J. Sax < > >>>>> mj...@apache.org > >>>>>>>> > >>>>>>>>>>>>>> wrote: > >>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> +1 (binding) > >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> On 9/3/20 6:16 AM, Bruno Cadonna wrote: > >>>>>>>>>>>>>>>>>> Hi, > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> I would like to start the voting on KIP-663 that > proposes > >>> to > >>>>>>> add > >>>>>>>>>>>>>> methods > >>>>>>>>>>>>>>>>>> to the Kafka Streams client to add and remove stream > >>> threads > >>>>>>>>>> during > >>>>>>>>>>>>>>>>>> execution. > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>> > >>>>>>>>>>>> > >>>>>>>>>> > >>>>>>> > >>>>> > >>> > https://cwiki.apache.org/confluence/display/KAFKA/KIP-663%3A+API+to+Start+and+Shut+Down+Stream+Threads > >>> > >>>>>>>>>>>>>>>>>> > >>>>>>>>>>>>>>>>>> Best, > >>>>>>>>>>>>>>>>>> Bruno > >>>>>>>>>>>>>>> > >>>>>>>>>>>>>> > >>>>>>>>>>>>> > >>>>>>>>>>>> > >>>>>>>>>>> > >>>>>>>>>> > >>>>>>>>>> > >>>>>>>>> > >>>>>>>> > >>>>>>> > >>>>>> > >>>>> > >>>>> > >>>> > >>> > >> > >> >
