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I talked to a few people about this issue during the offsite, but I
wanted to broadcast this before renaming in earnest. Usually
everyone has opinions about names :-)<br>
<br>
<a href="https://bugs.openjdk.java.net/browse/JDK-8139930">JDK-8139930
Rename G1 state variable to be meaningful</a> <br>
<blockquote>
Some of the core G1 state variables in G1CollectorState are
ambiguously named:
<br>
<br>
gcs_are_young, last_young_gc, last_gc_was_young <br>
<br>
Problems:
<br>
<ul>
<li>All gcs include the young gen, so taken literally "young"
doesn't add any information.
</li>
<li>"young" is shorthand for one of:</li>
<ul>
<li>"fully young" (which confusing with "full gc")</li>
<li>"young only", but the "only" is both silent and invisible.
</li>
</ul>
<li>
"last" is used in one variable to mean "previous", and in
another to mean "ultimate, maybe".</li>
<ul>
<li>"last_gc_was_young" vs. "last_young_gc".
</li>
</ul>
</ul>
</blockquote>
This issue is a general cleanup on its own, but is also a
prerequisite for
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<a href="https://bugs.openjdk.java.net/browse/JDK-8080226" title="
G1: Replace collector state booleans with explicit state
variable(s)" class="issue-link" data-issue-key="JDK-8080226">JDK-8080226</a>
(Replace collector state booleans with explicit state variable(s)?)
<br>
<br>
I'm working on two options:<br>
<b>Simple version:</b><br>
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<blockquote>gcs_are_young => mixed_mode
<br>
last_young_gc => consider_mixed_mode
<br>
last_gc_was_young => was_mixed_mode <br>
</blockquote>
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There is some indication that "last_gc_was_young" !=
(!"was_mixed_mode"). After a full GC, "last_gc_was_young" is set to
false. So it might make more sense to use an enum (Normal, Mixed,
Full) for "g1_mode" and "prev_g1_mode" variables.<br>
<br>
<b>Enum version:</b><br>
<blockquote>gcs_are_young => (g1_mode == NormalGC)
// can add helper predicate functions <br>
last_young_gc => consider_mixed_mode<br>
last_gc_was_young => (prev_g1_mode == NormalGC)<br>
full_collection => (g1_mode == FullGC)<br>
</blockquote>
Any opinions on this before I spin up jprt runs and webrevs?<br>
<br>
Thanks!<br>
<br>
- Derek<br>
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