Re: [hibernate-dev] v6 and load-event

Yes, I agree. On Thu, 28 May 2020, 22:11 Steve Ebersole, <steve(a)hibernate.org&gt; wrote: > Wanted to clarify - > > Regarding incremental addition of "surround listeners", so long as we are > all in agreement that this simply means there will be absolutely no > surround capability ***initially*** then I am fine with that. > > On Thu, May 28, 2020 at 4:10 PM Steve Ebersole <steve(a)hibernate.org&gt; > wrote: > >> Hm, the dynamic enable/disable stuff should be easy to handle, no? >> Depends on what specific library you are thinking of and exactly how that >> detail gets propagated to us. At the end of the day, its really as simple >> as protecting the creation of some of these objects with `if >> (enabled)`-type checks. >> >> But again, if you have specific details in mind we can take a look. >> >> Also, I think it is not at all a good idea to even plan for "different >> types of events". In fact I'm fine with getting rid of LoadEvent >> completely from that contract and simply directly passing the information >> that is likely useful. I mean at the end of the day a listener for load >> events is going to be interested in the same set of information. Yes, some >> will not need all of that information but that's not really a concern IMO. >> Especially if we inline the parameters and completely avoid the event >> object instantiation >> >> Regarding incremental addition of "surround listeners", so long as we >> are all in agreement that this simply means there will be absolutely no >> surround capability then I am fine with that. >> >> >> On Thu, May 28, 2020 at 3:55 PM Sanne Grinovero <sanne(a)hibernate.org&gt; >> wrote: >> >>> On Thu, 28 May 2020 at 21:27, Steve Ebersole <steve(a)hibernate.org&gt; >>> wrote: >>> > >>> > Any thoughts on this "continuation" approach? >>> >>> I love the pattern! Maybe we'll need also some ability to not capture >>> the state for events which don't have any? >>> >>> I wonder if that implies we'll need two different event contracts: one >>> for the listeners which need state and one for those which don't; but >>> I'm not eager to overcomplicate this. >>> >>> > Or maybe its just not important (yet) to handle "surround" handling? >>> >>> I'm confident that integration with tracing libraries would be very >>> useful and interesting to have - but indeed not having time to >>> research it properly I'm a bit afraid that it might need further >>> changes to reach excellent performance. >>> >>> For example one thing I remember is that with some libraries you're >>> supposed to have the option to enable/disable the profiling options >>> dynamically, and since there's an expectation of no overhead when it's >>> disabled this would need to imply having a way for the overhead of >>> allocating space for the captured state to "vanish": this might be a >>> bit more complicated, or need to be able to take advantage of JIT >>> optimisations. >>> >>> So if we end up thinking that such event APIs need to be different >>> depending on the need for state, perhaps indeed it's better to >>> postpone the design of those with state to when someone has time to >>> research an optimal integration with a tracing library. It might not >>> be too hard, I just haven't explored it myself yet. >>> >>> Maybe let's do this incrementally, considering the "continuation" >>> approach a next step? >>> >>> Thanks, >>> Sanne >>> >>> > >>> > On Wed, May 27, 2020 at 9:27 AM Steve Ebersole <steve(a)hibernate.org&gt; >>> wrote: >>> >> >>> >> Inline... >>> >> >>> >> On Wed, May 27, 2020 at 8:10 AM Sanne Grinovero <sanne(a)hibernate.org&gt; >>> wrote: >>> >>> >>> >>> At high level I agree, just have 3 more thoughts: >>> >>> >>> >>> # Regarding the "swap" of information between listeners - could that >>> >>> even work? I might have misunderstood something, but wouldn't we >>> >>> require listeners to run in some specific order for such swapping to >>> >>> work? >>> >> >>> >> >>> >> This is why we allow control over the ordering of the registered >>> listeners. And yes, that is and was a hokey solution. Nothing changes >>> there really if that is why you are using load listener. >>> >> >>> >> >>> >>> >>> >>> # The "surround advice" you mention for e.g. timing seems very >>> >>> interesting, especially as I'd love us to be able to integrate with >>> >>> tracing libraries - but these would need to be able to co-relate the >>> >>> pre-load event with some post-load event. How would that work? I'd >>> >>> expect these to need having a single listener implementation which >>> >>> implements both PreLoadEventListener and PostLoadEventListener, but >>> >>> also they'll likely need some capability to store some information >>> >>> contextual to the "event". >>> >> >>> >> >>> >> I was just thinking through this one as well. My initial thought >>> was exactly what you proposed - some combination of pre/post listener with >>> some ability to store state between. But that gets ugly. >>> >> >>> >> Another option I thought about is easier to illustrate, but >>> basically works on the principle of "continuation" many surround advice >>> solutions are based on: >>> https://gist.github.com/sebersole/142765fe2417492061e92726e7cb6bd8 >>> >> >>> >> I kept the name LoadEventListener there, but since it changes the >>> contract anyway I'd probably rename this to something like >>> SurroundLoadEventListener >>> >> >>> >> >>> >>> >>> >>> # To clarify on my previous comment regarding why I'd consider >>> having >>> >>> an actual Event class more maintainable: >>> >>> Sure we won't have inline classes widely used for a while, but I >>> >>> prefer planning for the long term - also we could start using them >>> >>> very soon via multi-release jars, which would simply imply that >>> users >>> >>> on newer JDKs would see more benefits than other users. >>> >>> But especially, such event instances are passed over and over across >>> >>> many methods; so in terms of maintenance and readability, such >>> methods >>> >>> would need to pass many parameters rather than one: the example made >>> >>> above is oversimplifying our use. Also while I understand it's >>> >>> unlikely, having a "cheap" event objects makes it easier to change >>> the >>> >>> exact types being passed on. >>> >>> BTW stack space is cheap but forcing many references to be passed >>> when >>> >>> one single reference could do might also have some performance >>> >>> implications since these are passed many times - I've never tested >>> >>> this scientifically though :) Inline objects would typically be >>> >>> allocated on the stack as well, but they don't force the JVM to do >>> so. >>> >>> >>> >>> >>> >>> Also while I said that it's unlikely we want to change those types, >>> >>> the very coming of inline types might actually encourage us to make >>> >>> changes in this area, even though these events have been stable for >>> >>> years; for example "String entityName" seems like an excellent >>> >>> candidate to become "EntityName typeIdentifier" - and then allow us >>> to >>> >>> improve the persister maps, which have been a bottleneck in the >>> past. >>> >>> So sure we could remove them and just pass parameters, we'd just >>> need >>> >>> to change more code if such a situation arises - I'm just highliting >>> >>> the drawbacks for our consideration, not recommending against it :) >>> >> >>> >> >>> >> Maybe its simply a difference of wording, but to me none of this >>> validates how keeping an event class is more maintainable. If you want to >>> say that eventually the overhead of having an actual event class will be >>> less, ok, but that's different. >>> >> >>> >> For sure though we'd have lots of uses for in-line value types >>> throughout the code base. Just not sure this really an argument for >>> keeping the event impl in-and-of-itself. >>> >> >>> >>