[foreign-abi] RFR: 8248560: Specify the behaviour of the ForeignLinker returned by CSupport::getSystemLinker [v4]

[Maurizio Cimadamore]

On Wed, 16 Sep 2020 11:41:25 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove public attribute name prefix
>
> src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/CLinker.java line 136:
> 
>> 134:      * the corresponding native stub will be deallocated.</p>
>> 135:      *
>> 136:      * <p>The method type of the target method handle is used for linking</p>
> 
> I think we can leave this out

@PaulSandoz mentioned (and I agree) that the terms upcalls and downcalls are colloquial, in the sense that it's
technically possible to pass an upcall stub to `downcallHandle`, so that it's no longer really making a downcall and,
conversely, it's possible to pass a native method handle to `upcallStub` so that it will not, strictly speaking,
execute an upcall to Java.

I think the real nature of what we're describing here is:

* given an address and a function descriptor, obtain a MethodHandle which can be used to execute the code at that address
  from Java code

* given a MethodHandle and a function descriptor, obtain a memory segment, whose base address can be passed to native
  code where a function pointer is expected

I don't know if the terms downcallHandle and upcallStub are the best to describe what these do.

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PR: https://git.openjdk.java.net/panama-foreign/pull/327