Thank you Steve. I have only one follow-up then. If the platform version is *always* a major version, does that imply that minor versions will not add API? The big benefit of MRJAR :-) is that I can provide separate code for different targeted runtimes. If 9.1 wouldn't add new API, then I am good. If that's the policy, great. I just want to confirm it is because I don't see too much of a technical difference between the two cases (8 to 9 vs 9.0 to 9.1). Does that make sense?
Cheers, Paul On Tue, Jul 19, 2016 at 1:41 PM, Steve Drach <steve.dr...@oracle.com> wrote: > Hi Paul, > > > I have some questions. I believe core-lib is the right place. If not > please > > let me know. > > This is the right place. First, the name was changed to Multi-Release > JAR, so it’s MRJAR (or Mr. Jar) instead of MVJAR. > > > > > 1) Given a Java 9 runtime, is there any perceptible difference between a > > non-multiversion jar, and a versioned jar which has placed all its > classes > > under /META-INF/versions/9 ? Pretend each jar has the same identical > > binaries/resources. > > There is probably a small difference in performance although I haven’t > measured it. Whether the difference is perceptible or not probably depends > on the characteristics of the sensor. > > > > > 2) Does the runtime care if the class version does not match what's under > > /META-INF/versions/9? For example, what if I have targeted a Java 8 class > > file format under versions/9? > > The MRJAR runtime does not care. However if you put a class file targeted > for Java 10 in the /META-INF/versions/9 directory and run it on a Java 9 > platform, you’ll probably get an error. > > > > > 3) Why does the new MVJAR JEP writeup [1] use versions/8 in the example? > > Because we don’t have a real example that uses Java 9 and the JEP was > written when we thought we’d target this feature for Java 8. > > > Is > > it simply for illustration, but I don't see how that's a useful example > > since it's an impossibility. There is no MVJAR support prior to Java 8 so > > isn't a better (and realer) example be /9 and /10? > > Yes, it would be better, but as I said, we don’t have a real world example > yet, so anything we do would be a contrived example. We probably need to > do something with that part of the JEP. > > > > > 3) The same MVJAR JEP writeup doesn't clearly indicate what is > considered a > > "platform version". All the examples show a single digit, but I believe > > Verona [2] has specificed the platform to include both major and minor > > versions. For example, Verona says the minor version may include > "revisions > > to standard APIs mandated by a Maintenance Release of the relevant > Platform > > Specification". Because it mentions platform, it should be possible to do > > /9, /9.0, and /9.1. Please advise? > > Platform versions are major versions, i.e. 8, 9, 10, etc. They are the > values derived from Runtime.Version::major > > > > > 4) Although MVJAR JEP writeup says "JAR metadata, such as that found in > the > > MANIFEST.MF file and the META-INF/services directory, need not be > > versioned." The keyword here is "need not" which is not the same as "can > > not" or "may not”. > > Yes, you are right, it’s incorrect. Perhaps it should say "JAR metadata, > such as that found in the MANIFEST.MF file and the META-INF/services > directory, are not versioned.” > > > So if it is needed, how does one version different > > services for different platforms? > > It can’t be done. > > > Can there be /META-INF under the > > appropriate versioned folder? > > Technically, it can be done but it won’t be interpreted as a “true” > META-INF directory, it’ll just be a path component for the jar entry. > > > Maybe /META-INF/versions/9/META-INF? > > You won’t achieve what you expect, depending of course on what you expect. > ;-) > > > I do not > > see anything in the JEP that says it's supported or non-supported. Please > > advise. > > It’s not supported. > > > > > [1] http://openjdk.java.net/jeps/238 > > [2] http://openjdk.java.net/jeps/223 > > > > Cheers, > > Paul > >
