On Sat, 10 Jan 2026 18:51:06 GMT, Liam Miller-Cushon <[email protected]> wrote:
>> This PR proposes adding a new overload to `MemorySegment::getString` that >> takes a known byte length of the content. >> >> This was previously proposed in https://github.com/openjdk/jdk/pull/20725, >> but the outcome of >> [JDK-8333843](https://bugs.openjdk.org/browse/JDK-8333843) was to update >> `MemorySegment#getString` to suggest >> >> >> byte[] bytes = new byte[length]; >> MemorySegment.copy(segment, JAVA_BYTE, offset, bytes, 0, length); >> return new String(bytes, charset); >> >> >> However this is less efficient than what the implementation of getString >> does after [JDK-8362893](https://bugs.openjdk.org/browse/JDK-8362893), it >> now uses `JavaLangAccess::uncheckedNewStringNoRepl` to avoid the copy. >> >> See also discussion in [this panama-dev@ >> thread](https://mail.openjdk.org/pipermail/panama-dev/2025-November/021193.html), >> and mcimadamore's document [Pulling the (foreign) >> string](https://cr.openjdk.org/~mcimadamore/panama/strings_ffm.html) >> >> Benchmark results: >> >> >> Benchmark (size) Mode Cnt Score Error >> Units >> ToJavaStringTest.jni_readString 5 avgt 30 55.339 ± 0.401 >> ns/op >> ToJavaStringTest.jni_readString 20 avgt 30 59.887 ± 0.295 >> ns/op >> ToJavaStringTest.jni_readString 100 avgt 30 84.288 ± 0.419 >> ns/op >> ToJavaStringTest.jni_readString 200 avgt 30 119.275 ± 0.496 >> ns/op >> ToJavaStringTest.jni_readString 451 avgt 30 193.106 ± 1.528 >> ns/op >> ToJavaStringTest.panama_copyLength 5 avgt 30 7.348 ± 0.048 >> ns/op >> ToJavaStringTest.panama_copyLength 20 avgt 30 7.440 ± 0.125 >> ns/op >> ToJavaStringTest.panama_copyLength 100 avgt 30 11.766 ± 0.058 >> ns/op >> ToJavaStringTest.panama_copyLength 200 avgt 30 16.096 ± 0.089 >> ns/op >> ToJavaStringTest.panama_copyLength 451 avgt 30 25.844 ± 0.054 >> ns/op >> ToJavaStringTest.panama_readString 5 avgt 30 5.857 ± 0.046 >> ns/op >> ToJavaStringTest.panama_readString 20 avgt 30 7.750 ± 0.046 >> ns/op >> ToJavaStringTest.panama_readString 100 avgt 30 14.109 ± 0.187 >> ns/op >> ToJavaStringTest.panama_readString 200 avgt 30 18.035 ± 0.130 >> ns/op >> ToJavaStringTest.panama_readString 451 avgt 30 35.896 ± 0.227 >> ns/op >> ToJavaStringTest.panama_readStringLength 5 avgt 30 4.565 ± 0.038 >> ns/op >> ToJavaStringTest.panama_readStringLength 20... > > Liam Miller-Cushon has updated the pull request with a new target base due to > a merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains 21 additional > commits since the last revision: > > - Merge branch 'master' into JDK-8369564 > - Rename the parameter of getString from length to byteLength > - Merge branch 'master' into JDK-8369564 > - Review feedback > - Update discussion of truncated reads of strings containing \0 > - Return the number of copied bytes > - More javadoc updates > - Use Utils.checkNonNegativeArgument > - Review feedback > > * handle numChars + srcIndex overflow, and add tests > * replace yen with a character that round trips > - Improve test coverage, and more fixes > - ... and 11 more: https://git.openjdk.org/jdk/compare/87751392...e2cc6f0b src/java.base/share/classes/java/lang/foreign/MemorySegment.java line 1351: > 1349: * largest string supported by the platform > 1350: * @throws IndexOutOfBoundsException if {@code offset < 0} > 1351: * @throws IndexOutOfBoundsException if {@code offset > byteSize() > - length} Suggestion: * @throws IndexOutOfBoundsException if {@code offset > byteSize() - byteLength} I assume this was missed? src/java.base/share/classes/java/lang/foreign/MemorySegment.java line 1356: > 1354: * @throws WrongThreadException if this method is called from a > thread {@code T}, > 1355: * such that {@code isAccessibleBy(T) == false} > 1356: * @throws IllegalArgumentException if {@code length < 0} Suggestion: * @throws IllegalArgumentException if {@code byteLength < 0} ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/28043#discussion_r2679311350 PR Review Comment: https://git.openjdk.org/jdk/pull/28043#discussion_r2679311392
