RFR: 8274338: com/sun/jdi/RedefineCrossEvent.java failed "assert(m != __null) failed: NULL mirror"

[David Holmes]

On Wed, 13 Oct 2021 20:29:46 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> The MultiArray_lock isn't held when restoring shared arrays, so an observer can find one that isn't completely restored.
> Tested with tier1-3 in progress, and CDS tests locally.  Not really reproduceable otherwise even with sleeps.

Hi Coleen,

Given the array_klasses() is accessed lock-free (using acquire/release semantics) I don't see how adding this lock prevents a partially restored array from being observed? The lock prevents concurrent restoration operations, and prevents restoration concurrently with creation (if that is even possible), but readers are still lock-free AFAICS.

Thanks,
David

src/hotspot/share/oops/instanceKlass.cpp line 2588:

> 2586:   if (array_klasses() != NULL) {
> 2587:     // To get a consistent list of classes we need MultiArray_lock to ensure
> 2588:     // array classes aren't observed while they are being created.

s/created/restored

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PR: https://git.openjdk.java.net/jdk/pull/5935