[lworld] Integrated: 8286824: [lworld] WeakHashMap for value classes

[Roger Riggs]

On Thu, 30 Jun 2022 14:03:31 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> WeakHashMap uses WeakReference for keys, allowing it to retain only keys and values that are strongly referenced elsewhere.
> 
> The behavior of WeakReference (or any Reference class) is not defined for value objects.
> 
> Four (4) behaviors are proposed for WeakHashMap to give the developer a choice:
>  - SOFT - Keys that are value objects are retained until memory pressure clears soft references; then the keys that are value objects are removed automatically
>  - STRONG - Keys are value objects are retained until they are explicitly removed
>  - THROW - Keys that are value objects can not be put into the map; UnsupportedOperationException is thrown
>  - DISCARD - Keys that are value objects are silently discarded; as if they were removed immediately without being visible
> 
> The default is SOFT - key/values are removed when there is memory pressure.
> Entries will be removed automatically at some point, though less deterministically than with WeakReferences.

This pull request has now been integrated.

Changeset: a4c6473b
Author:    Roger Riggs <rriggs at openjdk.org>
URL:       https://git.openjdk.org/valhalla/commit/a4c6473bf48541170792305f97456b24fdb49528
Stats:     466 lines in 3 files changed: 460 ins; 1 del; 5 mod

8286824: [lworld] WeakHashMap for value classes

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PR: https://git.openjdk.org/valhalla/pull/718