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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">the nmethod entry barrier used by G1 keeps oop constants of nmethods alive [1].<o:p></o:p></p>
<p class="MsoNormal">As I see it this is only needed if actually constant fields (final or @Stable) are changed after initialization (see JDK-8288970).<o:p></o:p></p>
<p class="MsoNormal">Is this correct or are there other cases? [2]<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">If correct then I'd think it isn't the best solution to the issue. (a) the<o:p></o:p></p>
<p class="MsoNormal">keep-alive is almost always redundant (b) it is imprecise and can hinder<o:p></o:p></p>
<p class="MsoNormal">unloading of unreachable code because class loaders of inlined or devirtualized<o:p></o:p></p>
<p class="MsoNormal">calls are added to the nmethods constants. (c) nmethods with a stale constant<o:p></o:p></p>
<p class="MsoNormal">value are kept as long as they are called (d) the stale constant value might be<o:p></o:p></p>
<p class="MsoNormal">persisted somewhere which could cause inconsistency.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I'd like to get some feedback on this because I wonder if I should REDO<o:p></o:p></p>
<p class="MsoNormal">JDK-8297487 at all (<span lang="DE">after </span>BACKOUT JDK-8299956).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks, Richard.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[1] Keepalive of nmethod entry barrier used by G1:<o:p></o:p></p>
<p class="MsoNormal"> <a href="https://github.com/openjdk/jdk/blob/08b24ac7aacaff32577dc07e77ed0961dd804904/src/hotspot/share/gc/shared/barrierSetNMethod.cpp#L100-L103">
https://github.com/openjdk/jdk/blob/08b24ac7aacaff32577dc07e77ed0961dd804904/src/hotspot/share/gc/shared/barrierSetNMethod.cpp#L100-L103</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[2] Could be Loom but I wouldn't see why the keep-alive would be needed there. Otherwise it should be unlikely. After all G1 was working well w/o it.<o:p></o:p></p>
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