RFR: 8261413: Shenandoah: Disable class-unloading in I-U mode

[Aleksey Shipilev]

On Tue, 9 Feb 2021 11:58:58 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> JDK-8261341 describes a serious problem with I-U mode and class-unloading. Let's disable class-unloading in I-U for now as a workaround.
> 
> Testing:
>  - [ ] hotspot_gc_shenandoah
>  - [ ] tier1 (+UseShenandoahGC +IU)
>  - [x] runtime/CreateMirror/ArraysNewInstanceBug.java (+UseShenandoahGC +IU +aggressive) many times in a row w/o failure

Changes requested by shade (Reviewer).

src/hotspot/share/gc/shenandoah/mode/shenandoahIUMode.cpp line 37:

> 35: 
> 36: void ShenandoahIUMode::initialize_flags() const {
> 37:   // See: https://bugs.openjdk.java.net/browse/JDK-8261341

No need for this comment, as the message prints it out.

src/hotspot/share/gc/shenandoah/mode/shenandoahIUMode.cpp line 39:

> 37:   // See: https://bugs.openjdk.java.net/browse/JDK-8261341
> 38:   if (FLAG_IS_CMDLINE(ClassUnloading) && ClassUnloading) {
> 39:     log_warning(gc)("Shenandoah I-U mode forces -XX:-ClassUnloading, for decails, see https://bugs.openjdk.java.net/browse/JDK-8261341");

"Shenandoah I-U mode sets -XX:-ClassUnloading; see JDK-8261341 for details"

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PR: https://git.openjdk.java.net/jdk/pull/2477