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<p class="MsoNormal"><span style="font-size:11.0pt">I’m more thinking that the API already provides all the important entries and conversion from and to `MemorySegment` can be done by simple call of `MemorySegment::toArray` and `MemorySegment::ofArray`.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">David Lloyd <david.lloyd@redhat.com><br>
<b>Date: </b>Friday, 21 March 2025 at 13:37<br>
<b>To: </b>Adam Sotona <adam.sotona@oracle.com><br>
<b>Cc: </b>classfile-api-dev@openjdk.org <classfile-api-dev@openjdk.org><br>
<b>Subject: </b>[External] : Re: Class files in ByteBuffer<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">Please have a look at the PR. If you feel the API surface has grown too much, maybe removing the `ByteBuffer` variants is a logical step, since users can always wrap a `ByteBuffer`
with a `MemorySegment`? If you could comment on the PR if you feel that to be the case, I would appreciate it.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">Thanks.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt">On Thu, Mar 20, 2025 at 4:09</span><span style="font-size:12.0pt;font-family:"Arial",sans-serif"> </span><span style="font-size:12.0pt">PM Adam Sotona <<a href="mailto:adam.sotona@oracle.com">adam.sotona@oracle.com</a>>
wrote:<o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">I’m sorry to join the discussion a bit late.</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><span style="font-size:12.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Here are the points to consider:</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<li class="m1102407431525991501msolistparagraph" style="mso-list:l0 level1 lfo1">
<span style="font-size:11.0pt">Class-File API is implementation is after many rounds of performance optimizations purely based on byte arrays.</span><o:p></o:p></li><li class="m1102407431525991501msolistparagraph" style="mso-list:l0 level1 lfo1">
<span style="font-size:11.0pt">Internal use of ByteBuffer has been removed from the implementation, as it caused significant JDK bootstrap performance regression.</span><o:p></o:p></li><li class="m1102407431525991501msolistparagraph" style="mso-list:l0 level1 lfo1">
<span style="font-size:11.0pt">Enormous amount of work has been spent on the API surface reduction and removal of all unnecessary “conveniences”.</span><o:p></o:p></li></ul>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><span style="font-size:12.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt">Adam</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><span style="font-size:12.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><span style="font-size:12.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt"> </span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">classfile-api-dev <<a href="mailto:classfile-api-dev-retn@openjdk.org" target="_blank">classfile-api-dev-retn@openjdk.org</a>> on behalf of David Lloyd <<a href="mailto:david.lloyd@redhat.com" target="_blank">david.lloyd@redhat.com</a>><br>
<b>Date: </b>Thursday, 20 March 2025 at 21:11<br>
<b>To: </b><a href="mailto:classfile-api-dev@openjdk.org" target="_blank">classfile-api-dev@openjdk.org</a> <<a href="mailto:classfile-api-dev@openjdk.org" target="_blank">classfile-api-dev@openjdk.org</a>><br>
<b>Subject: </b>Re: Class files in ByteBuffer</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">I've opened a bug [1] and pull request [2] incorporating this discussion (more or less). I've implemented support for
both `MemorySegment` and `ByteBuffer`, but this could be revisited if it doesn't look OK. The implementation is not terribly invasive for now, only grabbing a few low-hanging optimizations.</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">[1] </span><span style="font-size:12.0pt"><a href="https://bugs.openjdk.org/browse/JDK-8352536" target="_blank"><span style="font-family:"Arial",sans-serif">https://bugs.openjdk.org/browse/JDK-8352536</span></a><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">[2] </span><span style="font-size:12.0pt"><a href="https://urldefense.com/v3/__https:/github.com/openjdk/jdk/pull/24139__;!!ACWV5N9M2RV99hQ!MNdgtt56CgKWQQak5PkwC2t1L1q0tTZrT2fqzVPHYo3jer5CUfysIIx9uMuCoLb27YGoQWuUDgu3s_h8ZhlN-w$" target="_blank"><span style="font-family:"Arial",sans-serif">https://github.com/openjdk/jdk/pull/24139</span></a><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">On Mon, Mar 10, 2025 at 12:38</span><span style="font-size:12.0pt;font-family:"Arial",sans-serif"> </span><span style="font-size:12.0pt">PM David
Lloyd <<a href="mailto:david.lloyd@redhat.com" target="_blank">david.lloyd@redhat.com</a>> wrote:<o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">When defining a class in the JDK, one may either use a byte array or a byte buffer to hold the contents of the class.
The latter is useful when (for example) a JAR file containing uncompressed classes is mapped into memory. Thus, some class loaders depend on this form of the API for class definition.</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> <o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">If I were to supplement such a class loader with a class transformation step based on the class file API, I would have
to copy the bytes of each class on to the heap as a byte[] before I could begin parsing it. This is potentially expensive, and definitely awkward.</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif"> </span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">After transformation, it doesn't really matter if you have a byte[] or ByteBuffer because either way, the class can
be defined directly.</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif"> </span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">It would be nice if the class file parser could accept either a byte[] or a ByteBuffer. I did a quick bit of exploratory
work and it looks like porting the code to read from a ByteBuffer instead of a byte[] (using ByteBuffer.wrap() for the array case) would be largely straightforward *except* for the code which parses UTF-8 constants into strings. Also there could be some small
performance differences (maybe positive, maybe negative) depending on how the buffer is accessed.</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif"> </span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">Is this something that might be considered?</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span class="m1102407431525991501gmailsignatureprefix"><span style="font-size:12.0pt">--
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">- DML • he/him<o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">- DML • he/him<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt">- DML • he/him<o:p></o:p></span></p>
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