JEP 442: Foreign Function & Memory API => why is it again preview API?

[forax at univ-mlv.fr]

----- Original Message -----
> From: "Uwe Schindler" <uschindler at apache.org>
> To: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "core-libs-dev" <core-libs-dev at openjdk.org>
> Sent: Wednesday, May 17, 2023 9:13:35 AM
> Subject: Re: JEP 442: Foreign Function & Memory API => why is it again preview API?

> Hi Remi,
> 
> thanks for the reponse!
> 
>>> yesterday Apache Lucene got the information that JDK 21 got the project
>>> panama JEP 442 update and I implemented it already in our source tree.
>>>
>>> Unfortunately the API is again marked "preview", but JDK 21 is "LTS
>>> release". Many of our users (Elasticserach, Solr) will be switching to
>>> this version. We were really hoping that the java.lang.foreign API is
>>> finished at that time. I checked the changes in our code: just a rename
>>> of a method and FileChannel#map now takes Arena instead of Scope.
>> I see that Alan and Maurizio have already answer to your other points.
>>
>> Having preview features and being a LTS are to separate concerns.
>> Being a LTS is about support, having preview features is about having feedback
>> before finalizing an API.
>>
>> Java 17 was released with preview features, Java 21 will be.
> 
> Yes that's the case. But Java 17 did not have any "runtime visible"
> preview features, only compiler had preview features. For public
> libraries out there (open source on Maven central like Lucene), people
> don't care how they are produced by a compiler. So enhanced switch
> statements or similar stuff is a bit different than the current problem
> where the preview features are visible at runtime.

Not true, most of the language changes in preview also have a corresponding runtime visible API marked as preview API.
In case of jdk17, the SwitchBootstraps API is marked as preview API
  https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/runtime/SwitchBootstraps.html

> 
> Some related note: I don't understand why classes compiled with preview
> SYNTAX features of the Java compiler need to be marked with the preview
> bit; IMHO compiler outputs should only be marked as preview if they use
> preview APIs. There should be no risk in running the compiler output of
> preview switch or instanceof statements without preview features enabled.

Because a syntax feature usually also requires a support API, either at runtime or at compile time :)
Records has java.lang.Record, Text blocks has String.stripIndent, etc

> 
> Uwe

Rémi

> 
> --
> Uwe Schindler
> uschindler at apache.org
> ASF Member, Member of PMC and Committer of Apache Lucene and Apache Solr
> Bremen, Germany
> https://lucene.apache.org/
> https://solr.apache.org/