[foreign-memaccess+abi] RFR: 8274602: Generalize UpcallStub into NativeSymbol [v2]

[Duncan Gittins]

I've just run "git pull" on panama-foreign ("git branch" shows
foreign-jextract) - it looks like jextract is missing the changes for
removal of CLinker.UpcallStub:

c:\jdk\panama-foreign\src\jdk.incubator.jextract\share\classes\jdk\internal\clang\libclang\CXCursorVisitor.java:38:
error: cannot find symbol
    static CLinker.UpcallStub allocate(CXCursorVisitor fi) {
                          ^

Am I basing my builds off the right branch if I just want to occasionally
refresh with Panama changes?

Kind regards

Duncan

On Tue, 5 Oct 2021 at 18:09, Jorn Vernee <jvernee at openjdk.java.net> wrote:

> On Tue, 5 Oct 2021 14:34:55 GMT, Maurizio Cimadamore <
> mcimadamore at openjdk.org> wrote:
>
> >> It might sometimes be useful to define a custom symbol lookup which
> returns symbols backed by a library that can be unloaded dynamically (e.g.
> using dlopen).
> >> We indeed have all the pieces to get there, except that symbnol lookup
> returns a memory address, which is not a scoped entity.
> >>
> >> To address this, I propose that we add a new sealed interface/final
> class (`NativeSymbol`) which implements `Addressable` and is used in two
> places:
> >> * as a return value for a symbol lookup
> >> * as a proxy for an upcall stub
> >>
> >> In other words, `NativeSymbol` is used to reference to some symbol in
> some library, where the library can have a given scope. Upcall stubs are
> just a special case where the upcall symbol is synthetized on the fly by
> the VM. With this in place, I think we can drop `CLinker.UpcallStub` and
> just use an "anonymous` NativeSymbol to represent upcall stubs.
> >>
> >> With this, it should be possible to define a dlopen-based lookup such
> as the one below:
> >>
> https://github.com/sundararajana/panama-jextract-samples/blob/master/dlopen/Dlopen.java
> >>
> >> In a way that is completely *safe* - that is, so that it is not
> possible for a library to be unloaded while a function is being executed
> (even when the scope  associated to the native symbol is shared).
> >
> > Maurizio Cimadamore has updated the pull request with a new target base
> due to a merge or a rebase. The incremental webrev excludes the unrelated
> changes brought in by the merge/rebase. The pull request contains ten
> additional commits since the last revision:
> >
> >  - Merge branch 'foreign-memaccess+abi' into native_symbol
> >  - Use NativeSymbol in downcallHandle
> >  - Merge branch 'foreign-memaccess+abi' into native_symbol
> >  - Add missing copyright headers
> >  - Merge branch 'foreign-memaccess+abi' into native_symbol
> >  - Fix QSort benchmark
> >  - Add scope check
> >    Add test
> >  - Merge branch 'foreign-memaccess+abi' into native_symbol
> >  - Initial push
>
> Marked as reviewed by jvernee (Committer).
>
> Latest changes look very good! Thanks.
>
> -------------
>
> PR: https://git.openjdk.java.net/panama-foreign/pull/589
>