[foreign-jextract] RFR: API refresh - part two (jextract edition)

[Paul Sandoz]

On Thu, 7 Oct 2021 17:06:20 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> This patch fixes jextract to work with the latest API changes.
> 
> The patch reintroduces overloads for foreign function wrappers which take a scope (since ResourceScope is no longer a subtype of SegmentAllocator).
> 
> We will consider later whether to drop these overloads; it is likely that the majority of jextract clients will already have an allocator somewhere, so the extra code is not necessary. On the other hand, if we want overloads, then I think it would also be useful to add an overload that takes a `MemorySegment` and converts it into a `prefixAllocator` (so that clients can store result of foreign function which returns a struct-by-value in a pre-existing segments).
> 
> I've made some improvements to the string conversion logic; in a lot of places we were creating a scope, then doing a malloc to allocate a temporary CXString, then extract a Java String from the CXString, and dispose/free the CXString. Since jextract is single-threaded, I replaced all that with an high-order function which takes a segment supplier, and uses a prefix allocator under the hood. This should be way more efficient than what we had - and string conversion is quite frequent in libclang (e.g. `CXCursor::spelling`).
> 
> The patch passes all tests.

src/jdk.incubator.jextract/share/classes/jdk/internal/clang/LibClang.java line 50:

> 48:     private static final boolean IS_WINDOWS = System.getProperty("os.name").startsWith("Windows");
> 49: 
> 50:     final static SegmentAllocator IMPLICIT_ALLOCATOR =

That's might be a useful addition as a constant on `SegmentAllocator`.

src/jdk.incubator.jextract/share/classes/jdk/internal/clang/LibClang.java line 94:

> 92:      * conversion. The size of the prefix segment is set to 256, which should be enough to hold a CXString.
> 93:      */
> 94:     private final static SegmentAllocator stringAllocator = SegmentAllocator.prefixAllocator(

Suggestion:

    private final static SegmentAllocator STRING_ALLOCATOR = SegmentAllocator.prefixAllocator(

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PR: https://git.openjdk.java.net/panama-foreign/pull/594