[jdk17u] RFR: 8276205: Shenandoah: CodeCache_lock should always be held for initializing code cache iteration

[Aleksey Shipilev]

On Mon, 15 Nov 2021 15:58:43 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> I would like to backport this Shenandoah specific fix to jdk17u.
> 
> This patch fixed the bug that not holding CodeCache_lock while initializing concurrent nmethod iterations, that can lead to miscount number of concurrent walker and result assertion failure.
> 
> The patch fixed a bug that prevents iterators from walking nmethod concurrently due to holding CodeCache_lock during the walk.
> 
> The original patch does not apply cleanly, due to context changes. But the patch is small and simple, conflicts can be easily resolved manually.
> 
> 
> Test:
> - [x] hotspot_gc_shenandoah

So the "context" difference is that JDK 17u does not have JDK-8273300, which removed `CodeCache_lock` from `ShenandoahCodeRootsIterator`? If so, looks fine.

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Marked as reviewed by shade (Reviewer).

PR: https://git.openjdk.java.net/jdk17u/pull/262