RFR: 8344560: Add system property for patched runtime

[Alan Bateman]

On Wed, 20 Nov 2024 14:26:27 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?

I had hoped you would get more feedback on the proposal. If we do expose the property then I'm wondering about the JDK-specific properties documented in System.getProperties, and also thinking about java -XshowSettings output.

test/jdk/java/lang/System/patchedModule/ModulePatcherTest.java line 39:

> 37:  * @run main/othervm --patch-module=java.base=${test.classes} ModulePatcherTest true
> 38:  */
> 39: public class ModulePatcherTest {

The existing tests for --patch-module are in test/jdk/tools/launcher/modules/patch, we might want to see if we should just update one of the existing tests or move the new test with a name that makes it clear it's testing the property.

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PR Comment: https://git.openjdk.org/jdk/pull/22277#issuecomment-2489206819
PR Review Comment: https://git.openjdk.org/jdk/pull/22277#discussion_r1850743894