Would this mean that if there is a private method in MyPublicStableClass, changing which wouldn't break anything, could we still not change it?
On Thu, Oct 27, 2016 at 2:55 PM, Sangjin Lee <[email protected]> wrote: > Resurrecting an old thread as part of the YARN bug bash (YARN-5130). > > At minimum, I believe we agree to the following (do let me know if that is > not the case): > (1) If the class is declared Public/Stable, no changes to the class that > breaks the Stable contract should be made between non-major releases > **regardless > of the method visibility/stability**. For example, the following would > break the stability: > - adding a new abstract method, whether that method is stable, evolving, or > even private > - renaming a public method > Although it may be possible to have methods with weaker > stability/visibility, they still MUST not break the class contract. > > (2) We need to address the existing violations to ContainerStatus and > NodeReport by adding a default implementation for **minor releases**. > - ContainerStatus: YARN-3866 (2.8) > - NodeReport: YARN-4293 (2.8) > > There are subsequent changes to ContainerStatus by YARN-2882 and YARN-5430, > but they are marked 2.9.0. Is there going to be 2.9.0? If not, then these > might not matter as 3.0.0 permits backward incompatible changes. > > Thoughts? > > On Tue, May 31, 2016 at 10:48 AM, Sangjin Lee <[email protected]> wrote: > > > > > > > On Tue, May 31, 2016 at 10:10 AM, Chris Nauroth < > [email protected]> > > wrote: > > > >> I recommend that we update the compatibility guide with some text that > >> explicitly addresses subclassing/interface inheritance stability for > >> classes/interfaces annotated Stable. This is for our own benefit too. > (I > >> often refer back to that doc when I'm coding a patch that might have a > >> chance of being backwards-incompatible.) > >> > > > > I agree that making this distinction helps not only users but also the > > hadoop contributors. In addition to updating the compatibility guide, how > > about adding a new audience annotation for interfaces & abstract classes > > that spells out whether a 3rd-party is expected to extend/implement it? > > > > For example, some interface can be Public/Stable for use but could be > > off-limits in terms of extending/implementing it, while another can be > > Public/Stable for use and allowed to be extended but with an Evolving > > stability. It requires a little design, but should helps us a great deal > on > > both ends. My 2 cents. > > > > Sangjin > > > > > >> > >> --Chris Nauroth > >> > >> > >> > >> > >> On 5/31/16, 9:46 AM, "Karthik Kambatla" <[email protected]> wrote: > >> > >> >Argh! Totally my bad on YARN-2882. Kept missing the changes to > >> >ContainerStatus even after you pointed out. > >> > > >> >Filed YARN-5184 to fix this before we release it. Thanks for pointing > it > >> >out, Steve. > >> > > >> >On Tue, May 31, 2016 at 6:00 AM, Steve Loughran < > [email protected]> > >> >wrote: > >> > > >> >> > >> >> On 31 May 2016, at 05:44, Karthik Kambatla <[email protected] > <mailto: > >> >> [email protected]>> wrote: > >> >> > >> >> Inline. > >> >> > >> >> On Sat, May 28, 2016 at 11:34 AM, Sangjin Lee <[email protected] > >> <mailto: > >> >> [email protected]>> wrote: > >> >> I think there is more to it. The InterfaceStability javadoc states: > >> >> Incompatible changes must not be made to classes marked as > stable. > >> >> > >> >> And in practice, I don't think the class annotation can be > considered a > >> >> simple sum of method annotations. There is a notion of class > >> >>compatibility > >> >> distinct from method stability. One key example is interfaces and > >> >>abstract > >> >> classes as in this case. The moment a new abstract method is added, > the > >> >> class becomes incompatible as it would break all downstream > subclasses > >> >>or > >> >> implementing classes. That's the case even if *all methods are > declared > >> >> stable*. Thus, adding any abstract method (no matter what their > >> >> scope/stability is) should be considered in violation of the stable > >> >> contract of the class. > >> >> > >> >> Fair point. I was referring to them in the context of adding > @Evolving > >> >> methods to @Stable classes. Our policy states that "Classes not > >> >>annotated > >> >> are implicitly ³Private². Class members not annotated inherit the > >> >> annotations of the enclosing class." So, the annotation on a method > >> >> overrides that of the enclosing class. This seems pretty reasonable > to > >> >>me. > >> >> > >> >> > >> >> > >> >> My code wouldn't even compile because new abstract methods were added > >> >>to a > >> >> class tagged as stable. > >> >> > >> >> As far as I'm concerned, it doesn't meat the strict semantics of > >> >>"stable", > >> >> unless there is some nuance I'm missing. > >> >> > >> >> Therefore, I'm with Sangin: adding new abstract methods to an > existing > >> >> @Stable class breaks compatibility. Adding new non-abstract methods > >> >>‹fine. > >> >> It would have been straightforward to add some new methods to, say > >> >> ContainerReport, which were no-ops/exception raising, but which at > >> least > >> >> didn't break compilation. (though they may have broken codepaths > which > >> >> required the methods to act as getters/settes) > >> >> > >> >> Do you think there is reason to revisit this? If yes, we should > update > >> >> this for Hadoop 3. > >> >> > >> >> I'm not sure about revisiting. I'm raising the fact that changes to > >> >> classes marked as stable have broken code, and querying the validity > of > >> >> such an operation within the constraints of the 2.x codebase. > >> >> > >> >> And I'm raising it on yarn-dev, as that's where things broke. If we > do > >> >> want to revisit things, that'll mean a move to common-dev. > >> >> > >> >> > >> >> > >> >> Regarding interfaces and abstract classes, one future enhancement to > >> the > >> >> InterfaceStability annotation we could consider is formally > separating > >> >>the > >> >> contract for users of the API and the implementers of the API. They > >> >>follow > >> >> different rules. It could be feasible to have an interface as > >> >>Public/Stable > >> >> for users (anyone can use the API in a stable manner) but Private for > >> >> implementers. The idea is that it is still a public interface but no > >> >> third-party code should not subclass or implement it. I suspect a > fair > >> >> amount of hadoop's public interface might fall into that category. > That > >> >> itself is probably an incompatible change, so we might have to wait > >> >>until > >> >> after 3.0, however. > >> >> > >> >> Interesting thought. Agree that we do not anticipate users > sub-classing > >> >> most of our Public-Stable classes. > >> >> > >> >> There are also classes which we do not anticipate end-users to > directly > >> >> use, but devs might want to sub-class. This applies to pluggable > >> >>entities; > >> >> e.g. SchedulingPolicy in fairscheduler. We are currently using > >> >> Public-Evolving to capture this intent. > >> >> > >> >> Should we add a third annotation in addition to Audience and > Stability > >> >>to > >> >> capture whether a class can be extended? Given the few classes we > >> >> anticipate being extended, this is likely lesser work. :) > >> >> > >> >> > >> >> Some options. > >> >> > >> >> -add a specific @PluginPoint extension with different stability > >> >> requirements.(stable, unstable, evolving). That tells implementors > how > >> >> likely things are to break. > >> >> > >> >> -Add some interface to indicate really, really, unstable. That comes > up > >> >> more with things like the Async FS APIs, where the discussion there > is > >> >> about how it may change radically. > >> >> > >> >> Something like @Experimental could be that. That means not just "can > >> >> change" but "can go away" > >> >> > >> > >> > >> --------------------------------------------------------------------- > >> To unsubscribe, e-mail: [email protected] > >> For additional commands, e-mail: [email protected] > >> > >> > > >
