Provide a MemorySegment API to read strings with known lengths

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    • Type: Enhancement
    • Resolution: Unresolved
    • Priority: P4
    • 27
    • Affects Version/s: None
    • Component/s: core-libs

      After JDK-8333843, the javadoc for MemorySegment#getString suggests the following pattern for reading strings of known length:

          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 it uses JavaLangAccess::uncheckedNewStringNoRepl to avoid the copy.

      It is possible that in the future C2 will be able to optimize away the copy for the known length pattern (see JDK-8364418), but it can't do that for current JDK versions, and it sounds like there are some challenges to doing that optimization.

      Given all that, I think it makes sense to reconsider the possibility of adding an overload of MemorySegment#getString to read strings with known lengths, which would offer the same performance as the null-terminated getString, and avoid the copy of the byte[].

            Assignee:
            Liam Miller-Cushon
            Reporter:
            Liam Miller-Cushon
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              Created:
              Updated: