RFR: 8212879: Make JVMTI TagMap table concurrent [v2]

[Coleen Phillimore]

On Mon, 2 Nov 2020 15:45:18 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> Because it crashed with my changes and didn't without.  I cannot recollect why.
>
> I thought that we didn't load the archived heap from CDS, if JVMTI heap walker capabilities are in place, as we didn't want this kind of interactions. But maybe I'm missing something, since you said having this if statement here made a difference.

Now I remember.  I added an assert in JvmtiTagMapTable::find() for oop != NULL which didn't exist in the current hashmap code.  The current hashmap code just didn't find a null oop.  I tracked it down to the fact that we're finding dormant objects whose class hasn't been loaded yet.

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PR: https://git.openjdk.java.net/jdk/pull/967