$ java --sun-misc-unsafe-memory-access=allow -cp build Equivalence     (Unsafe, VarHandle and FFM side by side)
field CAS: Unsafe and the replacement gave the same 2000-step trace
field getAndAdd: 4 threads x 100000 -> total 400000 on every implementation
off-heap array: Unsafe and the replacement gave the same 2000-step trace
off-heap getAndAdd: 4 threads x 100000 -> sum 400000 on every implementation
copyFrom / clear: identical on every implementation
byte[] long access at offsets 0..32: Unsafe and VarHandle view agree
VarHandle view at offset 36 of a 40-byte array: ArrayIndexOutOfBoundsException
FFM read of element 4 in a 4-element segment: IndexOutOfBoundsException
FFM read after close: IllegalStateException: Already closed
ALL 170 CHECKS PASSED
exit=0

$ java --sun-misc-unsafe-memory-access=deny -cp build Equivalence --new-only     (replacements only)
field CAS: the replacement alone gave the same 2000-step trace
field getAndAdd: 4 threads x 100000 -> total 400000 on every implementation
off-heap array: the replacement alone gave the same 2000-step trace
off-heap getAndAdd: 4 threads x 100000 -> sum 400000 on every implementation
copyFrom / clear: identical on every implementation
byte[] long access at offsets 0..32: VarHandle view only
VarHandle view at offset 36 of a 40-byte array: ArrayIndexOutOfBoundsException
FFM read of element 4 in a 4-element segment: IndexOutOfBoundsException
FFM read after close: IllegalStateException: Already closed
ALL 67 CHECKS PASSED (new APIs only)
exit=0

$ java --sun-misc-unsafe-memory-access=deny -cp build Equivalence     (the Unsafe version under deny)
Exception in thread "main" java.lang.ExceptionInInitializerError
	at Equivalence.main(Equivalence.java:25)
Caused by: java.lang.UnsupportedOperationException: objectFieldOffset
	at jdk.unsupported/sun.misc.Unsafe.beforeMemoryAccessSlow(Unsafe.java:1822)
	at jdk.unsupported/sun.misc.Unsafe.beforeMemoryAccess(Unsafe.java:1787)
	at jdk.unsupported/sun.misc.Unsafe.objectFieldOffset(Unsafe.java:905)

$ java -cp build Equivalence     (JDK 25 default: one warning, then the same results)
WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by UnsafeFieldCounter (file:<build>/m/)
WARNING: Please consider reporting this to the maintainers of class UnsafeFieldCounter
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release
field CAS: Unsafe and the replacement gave the same 2000-step trace
field getAndAdd: 4 threads x 100000 -> total 400000 on every implementation
off-heap array: Unsafe and the replacement gave the same 2000-step trace