[foreign-memaccess+abi] RFR: 8294970: Add linker option for saving thread-locals that the VM can overwrite

[Maurizio Cimadamore]

On Tue, 25 Oct 2022 15:09:19 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> This patch adds a new linker option, called `preserveValue`, that can be used to save thread-local values such as `errno` and `GetLastError` that the VM might overwrite. It takes a list of names of the values to save. Values are saved into a MemorySegment passed by the user, that is allocated according to the layout associated with the returned `PreserveValue` instance.
>> 
>> The API for this is somewhat convoluted, as we have to account for:
>>  1. a different JVM implementation might not overwrite the same thread-locals, or non at all. Such JVM implementations should be free to support a different set of names to save, or none at all.
>>  2. it should be possible to save multiple values during a single call.
>> 
>> But, this API is also flexible enough for an implementation to choose any layout it wants for the MemorySegment into which the values are saved. In the current implementation it's just a set of ints, but this could be changed as well.
>> 
>> ---------
>> ### Progress
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>> 
>> 
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>
> test/jdk/java/foreign/TestLinker.java line 27:
> 
>> 25:  * @test
>> 26:  * @enablePreview
>> 27:  * @run junit TestLinker
> 
> I've changed this test to use junit 5, in order to take advantage of the `@ValueSource` annotation. Does this seem okay? Or should we avoid mixing testng and junit in our test suite?

Not sure - but I can only find one test  that has imports for `org.junit.jupiter.xyz`. Wouldn't it be easy to have a testng data provider with the two values, even if slightly more verbose?

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PR: https://git.openjdk.org/panama-foreign/pull/742