Integrated: 8256011: Shenandoah: Don't resurrect finalizably reachable objects

[Roman Kennke]

On Sat, 7 Nov 2020 20:10:14 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> In the weak-LRB we currently return referents when it is 'marked', that is when it's either reachable strongly or through a finalizable object. This means a finalizable object can be resurrected by Reference.get(), which is wrong. Only truly strongly reachable objects should be returned by Reference.get() during weak-reference-processing. 
> 
> I had to reconsider the way we call into runtime-LRBs from generated code for these reasons:
>  - We need to distinguish phantom, weak and strong reference strength, and native vs in-heap access. Those are two orthogonal dimensions
>  - We can have strong and phantom native referents, and strong and weak in-heap referents
>  - Native referents are never compressed
> 
> Note that this depends on PR#1140.
> 
> Testing:
>  - [x] hotspot_gc_shenandoah (x86_64, x64_32, aarch64)
>  - [x] tier1 +UseShenandoahGC +ShenandoahVerify
>  - [x] tier2 +UseShenandoahGC +ShenandoahVerify

This pull request has now been integrated.

Changeset: b0c28fad
Author:    Roman Kennke <rkennke at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/b0c28fad
Stats:     390 lines in 16 files changed: 107 ins; 87 del; 196 mod

8256011: Shenandoah: Don't resurrect finalizably reachable objects

Reviewed-by: shade, zgu

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PR: https://git.openjdk.java.net/jdk/pull/1109