RFR: 8292375: Convert ProtectionDomainCacheTable to ResourceHashtable [v7]

[Ioi Lam]

On Thu, 1 Sep 2022 06:51:21 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> “Mapping to itself” is how this table works internally. I am not sure if this information is useful here. But the purpose of this table is really to keep track of all PDs that have been registered and not yet garbage collected.
>
> "mapping to itself" is more useful than "mapping ... to a unique Weakhandle" - which is even more of an internal implementation detail. I found the use of this table very hard to discern based on the internal use of the hashtable, as there is no real mapping operation - we simply track if a PD has been seen or not. The use of the hashtable is purely for lookup convenience - we could instead have a linked-list of PD's that we traverse for lookup.
> So perhaps we drop my second sentence above, and move it to where the hashtable itself is declared?

"mapping a PD to a unique Weakhandle" is not an implementation detail. It's the only useful API provided by this class:


WeakHandle obj = ProtectionDomainCacheTable::add_if_absent(protection_domain);


and that's the reason I question why this table is needed at all.

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PR: https://git.openjdk.org/jdk/pull/10043