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

[Maurizio Cimadamore]

On 16/05/2023 19:03, - wrote:
> For FFI, I would prefer some parts of the FFI, especially generic ones
> like Indirect Var Handles, to be promoted from the preview status.
> They are useful for non-FFI purposes.
These parts (e.g. the additional var handle combinators in 
MethodHandles) are the only ones that could be finalized independently 
of the remainder of the FFM API, yes.
> Has FFI API considered promoting APIs out of preview incrementally,
> like how Virtual Threads and Scoped values are?

See my other email. FFM is composed of two biggie APIs, one for managing 
memory, and one for linking foreign functions. The lifetime abstractions 
cut across both APIs (and so do memory layouts, which are used to deal 
with memory dereference, but also to describe foreign types for the 
linker). So, I don't think there were ever concrete opportunities to 
split the two APIs (even if it would have been nice to do that).

Sometimes features can be decomposed nicely, and delivered 
incrementally. That has been the case for most Amber features, and also 
for Loom. Other times it is less practical to do so, as for FFM API, and 
patterns in switch + record patterns.

Maurizio

>
> Chen Liang
>
>
> On Tue, May 16, 2023 at 12:28 PM Remi Forax <forax at univ-mlv.fr> wrote:
>> ----- Original Message -----
>>> From: "Uwe Schindler" <uschindler at apache.org>
>>> To: "core-libs-dev" <core-libs-dev at openjdk.org>
>>> Sent: Tuesday, May 16, 2023 5:38:32 PM
>>> Subject: JEP 442: Foreign Function & Memory API => why is it again preview API?
>>> Hi,
>> Hi Uwe,
>>
>>> 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.
>>
>> Before Java 10, when we were doing feature release model, if a feature was not ready yet, either the release was delayed (Java 9 was delayed 3 times if i'm remembering correctly) or postponed to the next big release (Java Module was initially scheduled for Java 8). With the new cadence model, features that are not ready yet are marked as preview.
>>
>> I understand that you are eager to use MemorySegment in anger but since a looong time, Java features are only released when they are ready :)
>>
>> Also, it seems that we will have a LTS release every two years now, if a LTS had no preview, it means that we will not get any feedback for 1/4 of the releases.
>>
>>> Uwe
>>>
>> regards,
>> 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/