RFR: 8344560: Add system property for patched runtime [v3]

[Roger Riggs]

On Fri, 22 Nov 2024 17:04:38 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> Please review this simple patch which adds a new external system property `jdk.patched` when the runtime has been patched with the `--patch-module` switch. This is useful for two reasons: 1) it allows one to determine at run-time whether or not `--patch-module` has been used (by querying the said property) 2) allows tools, such as `jlink` doing the same without needing to expose internal properties the JVM sets on initialization.
>> 
>> Testing:
>> 
>> - [x] GHA (includes new test)
>> - [x] New jtreg test 
>> 
>> Thoughts?
>
> Severin Gehwolf has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Mention jdk.patched in System class

Adding the property is a patch around the lack of the real information still seems like unfortunate choice.
Getting early patch detection isn't reason enough to use a hack to get the information needed.
(Btw, Valhalla will be patching in a set of value based classes when --enable-preview is used, so there's knock work for that later)
If the fork was not next week, I'd ask for a better solution, later if not now.

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PR Comment: https://git.openjdk.org/jdk/pull/22277#issuecomment-2501232766