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<p class="MsoNormal"><span style="font-size:11.0pt">I’m sorry to join the discussion a bit late.<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">Here are the points to consider:<o:p></o:p></span></p>
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<li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo3"><span style="font-size:11.0pt">Class-File API is implementation is after many rounds of performance optimizations purely based on byte arrays.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo3"><span style="font-size:11.0pt">Internal use of ByteBuffer has been removed from the implementation, as it caused significant JDK bootstrap performance regression.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo3"><span style="font-size:11.0pt">Enormous amount of work has been spent on the API surface reduction and removal of all unnecessary “conveniences”.<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Adam<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>
<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">classfile-api-dev <classfile-api-dev-retn@openjdk.org> on behalf of David Lloyd <david.lloyd@redhat.com><br>
<b>Date: </b>Thursday, 20 March 2025 at 21:11<br>
<b>To: </b>classfile-api-dev@openjdk.org <classfile-api-dev@openjdk.org><br>
<b>Subject: </b>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">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.<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">[1] </span><a href="https://bugs.openjdk.org/browse/JDK-8352536"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">https://bugs.openjdk.org/browse/JDK-8352536</span></a><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">[2] </span><a href="https://github.com/openjdk/jdk/pull/24139"><span style="font-size:12.0pt;font-family:"Arial",sans-serif">https://github.com/openjdk/jdk/pull/24139</span></a><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"><o:p> </o:p></span></p>
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<p class="MsoNormal"><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 <</span><a href="mailto:david.lloyd@redhat.com"><span style="font-size:12.0pt">david.lloyd@redhat.com</span></a><span style="font-size:12.0pt">>
wrote:<o:p></o:p></span></p>
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<p class="MsoNormal"><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.<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;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.<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">After transformation, it doesn't really matter if you have a byte[] or ByteBuffer because either way, the class can be defined directly.<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">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.<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">Is this something that might be considered?<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 class="gmailsignatureprefix"><span style="font-size:12.0pt">--
</span></span><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">- DML • he/him<o:p></o:p></span></p>
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<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 class="gmailsignatureprefix"><span style="font-size:12.0pt">--
</span></span><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">- DML • he/him<o:p></o:p></span></p>
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