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Hello Eirik, this is a general problem caused by type profile pollution in bytecode of these constructors so that virtual calls become slow, fully virtual calls. I do not think this site is used frequent enough that warrants a monkey patch like that in ArrayList;
such monkey patches will be removed in the future shall the JVM provide a better specialization solution.</div>
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If you want to learn more about how type profile pollution works, feel free to check out the patch for <a href="https://bugs.openjdk.org/browse/JDK-8366424">https://bugs.openjdk.org/browse/JDK-8366424</a>, where there's a benchmark that explains how all these
pollutions happen.</div>
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Regards,</div>
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Chen Liang</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> core-libs-dev <core-libs-dev-retn@openjdk.org> on behalf of Eirik Bjørsnøs <eirbjo@gmail.com><br>
<b>Sent:</b> Wednesday, February 25, 2026 9:08 AM<br>
<b>To:</b> core-libs-dev <core-libs-dev@openjdk.org><br>
<b>Subject:</b> [External] : RFD: Specializing ArrayDeque copy constructor for ArrayDeque (and possibly ArrayList)</font>
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Hi, While looking into ArrayDeque: : addElements recently, I noticed that the copy constructor ArrayDeque(Collection) does not specialize for an ArrayDeque being passed in a similar fashion to what ArrayList does. By utilizing the ArrayListBulkOpsBenchmark</div>
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<div dir="ltr">Hi,
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<div>While looking into ArrayDeque::addElements recently, I noticed that the copy constructor ArrayDeque(Collection) does not specialize for an ArrayDeque being passed in a similar fashion to what ArrayList does.</div>
<div><br>
</div>
<div>By utilizing the ArrayListBulkOpsBenchmark and adopting it for ArrayDeque, I was able to test the performance impact of specializing ArrayDeque(Collection) for ArrayDeque.</div>
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<div>Results show a reduction in time/op ranging from 30% (1 element) to 75% (75 elements).</div>
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<div>I also experimented with a similar specialization for ArrayList which shows promising results, up to 50% faster for lists of size 75.</div>
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<div>However, there are many collections in the JDK and which combinations to specialize for is not obvious. Is further exploration here worthwhile?</div>
<div> </div>
<div>Cheers,</div>
<div>Eirik. </div>
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