RFR: 8292375: Convert ProtectionDomainCacheTable to ResourceHashtable [v7]

[Ioi Lam]

On Thu, 1 Sep 2022 04:12:32 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix comments, add assert.
>
> src/hotspot/share/classfile/protectionDomainCache.hpp line 33:
> 
>> 31: 
>> 32: // The ProtectionDomainCacheTable maps all java.security.ProtectionDomain objects that are
>> 33: // registered by DictionaryEntry::add_protection_domain() to a unique WeakHandle.
> 
> Now that I understand what this table does, this comment is confusing to me. The table maps each PD to itself (using the WeakHandle as the actual key and value) as a means to track which PDs have been seen/registered. I would describe it thus:
> 
> // The ProtectionDomainCacheTable records all of the java.security.ProtectionDomain instances that have
> // been registered by DictionaryEntry::add_protection_domain(). We use a hashtable to
> map each  PD 
> // instance to itself (using WeakHandles) to allow for fast lookup.

“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.

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