«IndexOutOfBoundsException: доступ за пределами сегмента...» при доступе к указателю, считанному из MemorySegment

Question

Я пытаюсь протестировать функции внешних функций и памяти Java 21. Вот мой код:

      public static void main(String[] args) {
        // 1. Find foreign function on the C library path
        Linker linker = Linker.nativeLinker();
        SymbolLookup stdlib = linker.defaultLookup();
        MethodHandle radixsort = linker.downcallHandle(stdlib.find("radixsort").orElseThrow(), FunctionDescriptor.ofVoid(ValueLayout.ADDRESS, ValueLayout.JAVA_INT, ValueLayout.ADDRESS, ValueLayout.JAVA_CHAR));
        // 2. Allocate on-heap memory to store four strings
        String[] javaStrings = {"mouse", "cat", "dog", "car"};

        // 3. Use try-with-resources to manage the lifetime of off-heap memory
        try (Arena offHeap = Arena.ofConfined()) {
            // 4. Allocate a region of off-heap memory to store four pointers
            MemorySegment pointers = offHeap.allocateArray(ValueLayout.ADDRESS, javaStrings.length);
            // 5. Copy the strings from on-heap to off-heap
            for (int i = 0; i < javaStrings.length; i++) {
                MemorySegment cString = offHeap.allocateUtf8String(javaStrings[i]);
                pointers.setAtIndex(ValueLayout.ADDRESS, i, cString);
                assert cString.getUtf8String(0).length() > 0;
            }
            // 6. Sort the off-heap data by calling the foreign function
            radixsort.invoke(pointers, javaStrings.length, MemorySegment.NULL, '\0');
            // 7. Copy the (reordered) strings from off-heap to on-heap
            for (int i = 0; i < javaStrings.length; i++) {
                MemorySegment cString = pointers.getAtIndex(ValueLayout.ADDRESS, i);
                javaStrings[i] = cString.getUtf8String(0);
            }
        } // 8. All off-heap memory is deallocated here
        catch (Throwable e) {
            throw new RuntimeException(e);
        }
        assert Arrays.equals(javaStrings, new String[]{"car", "c∞at", "dog", "mouse"});  // true
    }

но я сталкиваюсь с этой ошибкой:

Exception in thread "main" java.lang.RuntimeException: java.lang.IndexOutOfBoundsException: Out of bound access on segment MemorySegment{ heapBase: Optional.empty address:105553153094096 limit: 0 }; new offset = 0; new length = 1

На линии:

javaStrings\[i\] = cString.getUtf8String(0);Кажется, чтоMemorySegment cString = pointers.getAtIndex(ValueLayout.ADDRESS, i);возвращает MemorySegment с byteSize = 0

Когда я используюcString.getUtf8String(0);в исходной cString я не обнаружил ошибок.

Кажется, чтоpointers.setAtIndexиpointers.getAtIndexне сохраняйте byteSize MemorySegment. ?