RFR: 8307106: Allow concurrent GCs to walk CLDG without ClassLoaderDataGraph_lock

[David Holmes]

On Fri, 28 Apr 2023 13:15:20 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

> A concurrent GC with concurrent class unloading can't currently walk the CLDG without the CLDG_lock today. We should add some synchronization code so it can do that safely. This patch adds the missing bits.

Thanks for the additional explanations @fisk.

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13718#pullrequestreview-1410306107