[foreign-memaccess+abi] RFR: 8291639: Improve the ability to visualize a MemorySegment in human readable forms [v2]

[Maurizio Cimadamore]

On Wed, 3 Aug 2022 16:17:06 GMT, Per-Åke Minborg <duke at openjdk.org> wrote:

>> This PR imrproves the ability to visualize a `MemorySegment` in human-readable forms.
>> 
>> It exposes two new methods by adding them directly to the MemorySegment interface. There are other ways to add the methods (e.g. by exposing them via a utility class).
>> 
>> The methods
>> 
>> 
>>     /**
>>      * Returns a Stream of human-readable, lines with hexadecimal values for this memory segment.
>>      * <p>
>>      * The exact format of the stream elements is unspecified and should not
>>      * be acted upon programmatically. Loosely speaking, this method renders
>>      * a format similar to the *nix command "hexdump -C".
>>      * <p>
>>      * As an example, a memory segment created, initialized and used as follows
>>      * {@snippet lang = java:
>>      * MemorySegment memorySegment = memorySession.allocate(64 + 4);
>>      * memorySegment.setUtf8String(0, "The quick brown fox jumped over the lazy dog\nSecond line\t:here");
>>      * memorySegment.hexStream()
>>      *     .forEach(System.out::println);
>>      *}
>>      * might print to something like this:
>>      * {@snippet lang = text:
>>      * 0000000000000000  54 68 65 20 71 75 69 63  6B 20 62 72 6F 77 6E 20  |The quick brown |
>>      * 0000000000000010  66 6F 78 20 6A 75 6D 70  65 64 20 6F 76 65 72 20  |fox jumped over |
>>      * 0000000000000020  74 68 65 20 6C 61 7A 79  20 64 6F 67 0A 53 65 63  |the lazy dog.Sec|
>>      * 0000000000000030  6F 6E 64 20 6C 69 6E 65  09 3A 68 65 72 65 00 00  |ond line.:here..|
>>      * 0000000000000040  00 00 00 00                                       |....|
>>      *}
>>      * <p>
>>      * Use a {@linkplain MemorySegment#asSlice(long, long) slice} to inspect a specific region
>>      * of a memory segment.
>>      *
>>      * @return a Stream of human-readable, lines with hexadecimal values
>>      */
>>      default Stream<String> hexStream() {
>>         return MemorySegmentRenderUtil.hexStream(this);
>>     }
>> ``` 
>> 
>> and
>> 
>> 
>>     /**
>>      * Returns a human-readable view of this memory segment viewed through
>>      * the provided memory layout {@code lens}.
>>      * <p>
>>      * Lines are separated with the system-dependent line separator {@link System#lineSeparator() }.
>>      * Otherwise, the exact format of the returned view is unspecified and should not
>>      * be acted upon programmatically.
>>      * <p>
>>      * As an example, a memory segment viewed though the following memory layout lens
>>      * {@snippet lang = java:
>>      * var lens = MemoryLayout.structLayout(
>>      *         ValueLayout.JAVA_INT.withName("x"),
>>      *         ValueLayout.JAVA_INT.withName("y")
>>      * ).withName("Point");
>>      *}
>>      * 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 layout
>>      * lenses and is, in all cases, restricted by the inherent String capacity limit.
>>      *
>>      * @param lens  to use as a lens when viewing the memory segment
>>      * @return a view of the memory segment viewed through a memory layout lens
>>      * @throws OutOfMemoryError if the view exceeds the array size VM limit
>>      */
>>     default String viewThrough(MemoryLayout lens) {
>>         Objects.requireNonNull(lens);
>>         return MemorySegmentRenderUtil.viewThrough(this, lens);
>>     }
>
> Per-Åke Minborg has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Merge branch 'render' of https://github.com/minborg/panama-foreign into render
>  - Update to reflect most initial PR comments

src/java.base/share/classes/jdk/internal/foreign/MemorySegmentRenderUtil.java line 136:

> 134:      *
> 135:      * @param memorySegment to be viewed
> 136:      * @param memoryLayout  to use as a memoryLayout when viewing the memory segment

bad find/replace?

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PR: https://git.openjdk.org/panama-foreign/pull/695