[foreign-jextract] RFR: Update memory access and linker documents [v4]

[Maurizio Cimadamore]

On Thu, 25 Mar 2021 15:55:11 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> doc/panama_ffi.md line 66:
>> 
>>> 64: MemorySegment size = MemorySegment.allocateNative(C_INT);
>>> 65: MemoryAccess.setInt(size, 5);
>>> 66: foo.invokeExact(42, size);
>> 
>> I think this should call `size.address()` to be equivalent with the C code. Also, reachability of the segment is problematic in that case, so maybe this should switch to using an explicit resource scope.
>
> I've rewritten this section as I noted that it was referring to native method handles, which were not yet discussed. Instead I focussed on "creating a native array" as a way to demonstrate "clunkiness" of base memory access API.

As for deterministic deallocation, I've changed all samples to just rely on it - and in the very first case (e.g. call to strlen) I explain that going from a segment to an address is a bit tricky.

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PR: https://git.openjdk.java.net/panama-foreign/pull/475