[foreign-memaccess+abi] Integrated: 8264386: LibraryLookup should be more friendly with implicit unloading

[Ty Young]

Is the Addressable interface still necessary after removing Symbol? IIRC 
it was added to get a MemoryAddress from Symbol, MemoryAddress, 
MemorySegment, and MappedMemorySegment in a unified way, however with 
Symbol gone you either have a MemoryAddress already or you can just call 
MemorySegment.address(). The MemoryAddress.address() method was already 
silly with Addressable as you could redundantly create new MemoryAddress 
objects that represent the same thing, but now there doesn't seem to be 
any justification for it that I can tell.


On 3/29/21 6:47 PM, Maurizio Cimadamore wrote:
> On Mon, 29 Mar 2021 15:36:13 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:
>
>> Quoting from the PR:
>>
>> Dereferencing a segment from a LibraryLookup is possible, in the following form:
>>
>> LibraryLookup libLookup = ...
>> MemorySegment segment = libLookup.lookup("foo").asSegmentRestricted(....)
>>
>> The above code has a problem: there is no link between the produced segment and the original library lookup - meaning that, in principle, it's possible for the library to be unloaded when dereference occurs.
>>
>> After having discussed many alternatives with Jorn, the best way to address this conundrum would be to add an overload of `LibraryLookup::lookup` which takes a lyout and returns a segment.
>>
>> As part of this change I have also removed the LibraryLookup.Symbol API which seems unnecessary - now you can lookup an address or a segment. Of course, looking up a segment is creating a restricted segment (so it should be treated as unsafe).
>>
>> I've added a test to make sure that the new API works as expected.
> This pull request has now been integrated.
>
> Changeset: d70c1e40
> Author:    Maurizio Cimadamore <mcimadamore at openjdk.org>
> URL:       https://git.openjdk.java.net/panama-foreign/commit/d70c1e40
> Stats:     126 lines in 11 files changed: 48 ins; 30 del; 48 mod
>
> 8264386: LibraryLookup should be more friendly with implicit unloading
>
> Reviewed-by: psandoz, jvernee
>
> -------------
>
> PR: https://git.openjdk.java.net/panama-foreign/pull/480