[foreign-memaccess+abi] RFR: 8274157: java.foreign: Add method MemorySegment::isOverlapping [v2]

[Maurizio Cimadamore]

On Fri, 1 Oct 2021 12:20:33 GMT, Julia Boes <jboes at openjdk.org> wrote:

>> This change adds a method to the MemorySegment API that detects if two segments are overlapping.
>
> Julia Boes has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:
> 
>  - Merge branch 'foreign-memaccess+abi' into memseg-overlap
>  - refactor to overlap(MemorySegment), add offsetOf(MemorySegment)
>  - Merge branch 'foreign-memaccess+abi' into memseg-overlap
>  - address PR comments
>  - initial change

src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/MemorySegment.java line 333:

> 331:      *
> 332:      * @param other the segment to test for an overlap with this segment.
> 333:      * @return a new memory segment, or {@code null} if no overlap occurs.

Should we say a "new slice of this segment" instead of "a new segment" (both here an in the first sentence of the javadoc) ?

src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/MemorySegment.java line 350:

> 348:      *         segment, or -1L if no overlap occurs.
> 349:      */
> 350:     long offsetOf(MemorySegment other);

I think what I had in mind was slightly different:
* return postive, or negative offsets in case of overlaps (of course in the case of sub-slices, offsets will always be positive)
* throw if asked to compute an offset from heap to non-heap (or vice-versa).

src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/AbstractMemorySegmentImpl.java line 261:

> 259:             long offsetFromThat = that.offsetOf(this);
> 260:             long newSize = Math.min(this.byteSize() - offsetFromThis, that.byteSize() - offsetFromThat);
> 261:             return dup(offsetFromThis, newSize, mask, scope);

nitpick: you can probably use asSlice instead of dup?

test/jdk/java/foreign/TestSegmentOffsetOf.java line 1:

> 1: /*

We used to have a test for MemoryAddress.segmentOffset...
https://github.com/openjdk/jdk/blob/master/test/jdk/java/foreign/TestRebase.java
I wonder if that old test can be put to new use?

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PR: https://git.openjdk.java.net/panama-foreign/pull/585