LTW on Java 24 gives terminally deprecated warning related to sun.misc.Unsafe::objectFieldOffset usage

[aclement]

This topic again...

Tests in AspectJ that are attempting LTW on Java 24 will see:

WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor (file:XXX)
WARNING: Please consider reporting this to the maintainers of class org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release

Currently I think i will just allow the tests to pass if they see this, but at some point it all needs revisiting again, but I don't believe a proper solution has been negotiated yet.

[kriegaex]

@aclement, since last year, this is part of the workaround for the previous need of --add-opens java.base/java.lang=ALL-UNNAMED for LTW, ...

aspectj/loadtime/src/main/java/org/aspectj/weaver/loadtime/ClassLoaderWeavingAdaptor.java

Line 1133 in fc46e12

return unsafe.objectFieldOffset(overrideField);

... described in more details in the API docs:

aspectj/loadtime/src/main/java/org/aspectj/weaver/loadtime/ClassLoaderWeavingAdaptor.java

Lines 1053 to 1078 in fc46e12

	* Scaffolding for defining classes in arbitrary class loaders
	* <p>
	* Inspired by and shamelessly adapted from <a href="https://bit.ly/3w10oH5">Byte Buddy's {@code ClassInjector}</a>.
	* Special thanks to Byte Buddy (BB) author Rafael Winterhalter, who briefly mentioned this approach in a
	* <a href="https://bit.ly/3SjFOZY">GitHub comment</a> related to JDK issue
	* <a href="https://bugs.openjdk.org/browse/JDK-8200559">JDK-8200559</a>.
	* <p>
	* <b>Background:</b> Instead of BB, we use ASM and reflection as follows:
	* <ul>
	* <li>
	* Create a mirror class for {@link AccessibleObject} with a different package name in a separate, throw-away
	* class loader.
	* </li>
	* <li>
	* Use the mirror class to calculate the {@link Unsafe#objectFieldOffset(Field)} for boolean field
	* {@link AccessibleObject#override}, which is expected to be identical to the offset of the same field in the
	* original class.
	* </li>
	* <li>
	* After we have the offset, we can use it to override the field value in the original class, deactivating access
	* checks for {@link jdk.internal.misc.Unsafe#defineClass(String, byte[], int, int, ClassLoader, ProtectionDomain)},
	* the method we need to execute using a method handle.
	* </li>
	* </ul>
	* All these serve the sole purpose enable LTW without {@code --add-opens java.base/java.lang=ALL-UNNAMED} on the
	* JVM command line on JDK 16+, which was necessary for AspectJ 1.9.7 (Java 16) to 1.9.21 (Java 21).

As this approach has been borrowed from Byte Buddy, maybe its author, the experienced Java champion @raphw can help to figure out if there are any other ways to achieve the same which are still working (without warnings) on JDK 24+.

[raphw]

You can in theory migrate to jdk.internal.misc.Unsafe, but you would need to open that module. Would that be viable? With Instrumentation, you can open it using the API.

[kriegaex]

Thanks for the hint, @raphw. This is a tantalising thing to try, whenever I might find a sponsor for my work in this project. Until then, probably Andy will have implemented it already.