<div dir="ltr">Thanks Maurizio,<div><br></div><div>I think that looks great. It addresses the use-cases I'm aware of for reading and writing strings of known length, without null terminators.</div><div><br>I have a few small questions and comments.</div><div><br></div>> The number of bytes associated with chars is platform-dependent: it's 10 bytes on Windows, but 20 bytes on Linux. By having MemorySegment::getString work on units the only thing we need to worry about is that we specify the correct charset when reading the string -- e.g. UTF16 (on Windows) or UTF32 (on Linux).<div><br></div><div>I want to double-check my understanding of that example. Is the idea that you would read a code unit length from the struct Foo (5 in the example) and then depending on whether the API expected bytes or code units, you would have to do one of the following?</div><div><br>// with a code unit length<br>getString(0, /* code units */ 5, windows ? UTF16 : UTF32)<br><br>// vs. with a byte length<br>getString(0, /* bytes */ 5 * (windows ? 2 : 4), windows ? UTF16 : UTF32)</div><div><br></div><div>> Liam said protobuf uses byte lengths. Native strings probably use unit lengths</div><div><br></div><div>One of my colleagues working on protobuf pointed out I had described that imprecisely and offered the following clarification:<br><br>Its really that Protobuf just solely ever represents strings as UTF8 in native heap memory (even on windows where the OS APIs will expect utf16, if someone ever wanted to take use C++Protobuf strings to/from windows paths, they would actually have to convert utf8<>utf16 themselves); it means that byte and unit lengths are always the same for us when stored in native heap</div><div><br></div><div>Another small clarification - the doc mentions 'compressed strings', should that be 'compact strings'? (JEP 254 mentions there was an older 'compressed strings' feature in JDK 6?)</div><div><br></div><div>And one more thing - the doc discusses string lengths. In addition to the number of UTF-16 code units in the UTF-16 encoding of the string (String.length), and the number of unicode characters (codePointCount), it is sometimes desirable to know the number of code units in the encoded string. It's possible to do this with getBytes(charset).length, but similar to the other performance discussions here, it's expensive to create the array and throw it away, and an implementation outside the JDK can't benefit from the JDK's fast paths in StringSupport. In theory there could be a method like String#getEncodedLength(Charset) that returned the same value as getBytes(charset).length with better performance. Is that something you think could be interesting to consider, either as part of this proposal, or separately?</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Fri, Nov 7, 2025 at 5:40 PM Maurizio Cimadamore <<a href="mailto:maurizio.cimadamore@oracle.com">maurizio.cimadamore@oracle.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
<div>
<p>Hi,<br>
here's a document that outlines a more general strategy to read
and write strings from/to memory segments:</p>
<p><a href="https://cr.openjdk.org/~mcimadamore/panama/strings_ffm.html" target="_blank">https://cr.openjdk.org/~mcimadamore/panama/strings_ffm.html</a></p>
<p>As outlined in this thread, the enabling primitive for the
writing side is a factory that allows to view a Java string as a
read-only heap memory segment.</p>
<p>We believe the proposed strategy should provide better usability,
while at the same time leaving room for the implementation to "cut
corners", to make performance as good as possible.</p>
<p>Let us know what you think.</p>
<p>Cheers<br>
Maurizio<br>
</p>
<div>On 05/11/2025 12:45, Liam Miller-Cushon
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Thanks Maurizio, considering all of this
holistically makes sense. I look forward to hearing your
thoughts on it once you've had time to consider the options :)</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, Nov 4, 2025 at
11:21 PM Maurizio Cimadamore <<a href="mailto:maurizio.cimadamore@oracle.com" target="_blank">maurizio.cimadamore@oracle.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p><br>
</p>
<div>On 04/11/2025 15:23, Jorn Vernee wrote:<br>
</div>
<blockquote type="cite">
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div>Do you have thoughts on the best way to proceed
here? Do you think it makes sense to do
incrementally, or would you prefer to see all of
these related changes happen together under a
single issue?<br>
<br>
</div>
</div>
</div>
</blockquote>
<p>I don't have a preference. Since you've already started
a PR for enhancing getString, maybe you can focus on
that for now, and we'll file followup issues for the
others. Splitting things up might be nice since there's
probably some benchmarking work involved for each. I
think the copy and allocateFrom overload can be done in
one patch though.</p>
</blockquote>
<p>I think I sort of do have a preference :-)</p>
<p>My feeling is that we're dealing with 2-3 different APIs
that are all tightly interconnected. We have some ideas on
how to solve some (I think getString with explicit length
seems the most settled), but we're still playing with
other ideas for the others (like copy, or memory segment
views). And we also have to think about relationship with
SegmentAllocator.</p>
<p>For this reason, I'd prefer to think about it more
holistically and think about all the related APIs at once.</p>
<p>Once we get a consensus on how to proceed we can decide
whether to pursue them all in a single PR, or split them
into separate PRs.</p>
<p>But it would be unfortunate, I think, if the first PR
would later reveal to be a dead end for the other use
cases.</p>
<p>I plan to think about this some more (but I need some
more time).</p>
<p>Cheers<br>
Maurizio<br>
</p>
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</blockquote>
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</blockquote>
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</blockquote></div>