RFR: 8365400: enhance JFR to emit file and module metadata for class loading

[Erik Gahlin]

On Mon, 6 Oct 2025 18:15:51 GMT, Larry Cable <duke at openjdk.org> wrote:

> while existing class loading JFR events exist, none of these provide the path (if available) from which a class is loaded/defined, nor are they easily modified to do so from a compatibility standpoint.
> 
> therefore this ER/PR adds a simple JFR event that encapsulates a tuple of class and path that can be enabled in order to provide an audit/debug trail of locations (path, if available) from which a particular class is loaded/defined.
> 
> this association can be used for various "applications" such as basic auditing etc

I have not reviewed SecureClassLoader, as this is better done by people who are more knowledgeable in the area. That said, toExternalForm() appears to be a somewhat expensive function, so you may want to add a guard. Also check for null.

        ClassFileDefineEvent event = new ClassFileDefineEvent();
        if (event.isEnabled()) {
            event.definedClass = cls;
            if (cs != null) {
                URL location = cs.getLocation();
                if (location != null) {
                    event.path = location.toExternalForm();
                }
            }
            event.commit();   
        }
        
Could you also add the event to profile.jfc? Please remove "Name" from the label "Defined Class Name," as the whole class is serialized, and add a test to test/jdk/jdk/jfr/event/runtime.

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PR Comment: https://git.openjdk.org/jdk/pull/27656#issuecomment-3374488908