RFR: 8292375: Convert ProtectionDomainCacheTable to ResourceHashtable [v7]

[David Holmes]

On Thu, 1 Sep 2022 07:23:03 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> "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.

The fact it is a weakhandle is an implementation detail. The table simply records whether a PD (wrapped in a WeakHandle) has been seen.

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