RFR: 8354897: Support Soft/Weak Reference in AOT cache

[Ioi Lam]

On Thu, 24 Apr 2025 21:01:11 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> src/java.base/share/classes/jdk/internal/util/ReferencedKeyMap.java line 355:
>> 
>>> 353:             if (referent == null) {
>>> 354:                 // We don't need this key anymore. Add to stale queue
>>> 355:                 ((Reference)key).enqueue();
>> 
>> Is enqueue necessary here? Afaik this map only uses the queue to be alert of member reference being garbage collected and then remove stale elements. Since at this stage this map is no longer used, maybe `key.unused()` is sufficient?
>
> I'm not sure what you are proposing. But enqueue is used to ensure that inactive references are pruned from the data structure so that dumping only includes active references. This way, the JVM that loads these objects create these references as active and hence follow the usual life cycle that every other reference does. I want to avoid having a new "special" life cycles for dumped references.

The map is still being used (and will be stored into the AOT cache). The key no longer has a referent, so we need to remove the key from the map. Adding the key to the stale queue and calling `removeStaleReferences()` will accomplish this. `key.unused()` does not remove the key from the map.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/24757#discussion_r2059235560