[foreign-memaccess+abi] RFR: Add an internal MemoryInspection class

[Maurizio Cimadamore]

On Wed, 7 Sep 2022 11:29:11 GMT, Per Minborg <duke at openjdk.org> wrote:

> This PR adds a way of inspecting a `MemoryLayout` through a `MemoryLayout`.
> 
> 
>     /**
>      * Returns a human-readable view of the provided {@linkplain MemorySegment memory} viewed
>      * through the provided {@linkplain MemoryLayout layout} using the provided {@linkplain ValueLayoutRenderer renderer}.
>      * <p>
>      * The exact format of the returned view is unspecified and should not
>      * be acted upon programmatically.
>      * <p>
>      * As an example, a MemorySegment viewed though the following memory layout
>      * {@snippet lang = java:
>      * var layout = MemoryLayout.structLayout(
>      *         ValueLayout.JAVA_INT.withName("x"),
>      *         ValueLayout.JAVA_INT.withName("y")
>      * ).withName("Point");
>      *
>      * MemoryInspection.inspect(segment, layout, ValueLayoutRenderer.standard())
>      *     .forEach(System.out::println);
>      *
>      *}
>      * might be rendered to something like this:
>      * {@snippet lang = text:
>      * Point {
>      *   x=1,
>      *   y=2
>      * }
>      *}
>      * <p>
>      * This method is intended to view memory segments through small and medium-sized memory layouts.
>      *
>      * @param segment  to be viewed
>      * @param layout   to use as a layout when viewing the memory segment
>      * @param renderer to apply when rendering value layouts
>      * @return a view of the memory abstraction viewed through the memory layout
>      */
>     public static Stream<String> inspect(MemorySegment segment,
>                                          MemoryLayout layout,
>                                          ValueLayoutRenderer renderer) {

Looks good. I left some minor comments.

src/java.base/share/classes/jdk/internal/foreign/MemoryInspectionUtil.java line 232:

> 230:     }
> 231: 
> 232:     static final class SingleFunctionValueLayoutRenderer implements MemoryInspection.ValueLayoutRenderer {

As we discussed offline, perhaps using a BiFunction might be good enough for all practical purposes

src/java.base/share/classes/jdk/internal/foreign/MemoryInspectionUtil.java line 293:

> 291:     }
> 292: 
> 293: }

Watch out of missing newline

test/jdk/java/foreign/TestMemoryInspection.java line 47:

> 45: 
> 46: @Test
> 47: public class TestMemoryInspection {

The test is good, but it never initialized the segments to something meaningful. As such, the test will not detect issues e.g. when parsing elements of an array (e.g. the array test uses an array of 4 structs, but since the contents of the segment is all zeros, all the structs have same values).

test/jdk/java/foreign/TestMemoryInspection.java line 288:

> 286:     }
> 287: 
> 288: }

watch out for missing newline

-------------

Marked as reviewed by mcimadamore (Committer).

PR: https://git.openjdk.org/panama-foreign/pull/715