In our codebase we have an array-like datastructure class that allocates memory with sun.misc.Unsafe so it can accept a long as a size & index parameter. This class also uses the sun.misc.Unsafe function compareAndSwapLong to perform compare-and-swap (CAS) operations against elements of the array. This class produces un-silenceable warnings when compiled and per JEP 471 the functionality in sun.misc.Unsafe is now deprecated, so we are looking to update it to use Java’s newer unsafe APIs.

Java’s VarHandle class was introduced in JEP 193/Java 9 and is touted as a safe way to perform low-overhead CAS operations. However, it only appears to operate on existing safe datastructures; for example, to CAS an element of an array the docs show this example:

String[] sa = ...
VarHandle avh = MethodHandles.arrayElementVarHandle(String[].class);
boolean r = avh.compareAndSet(sa, 10, "expected", "new");

the docs then specify that the compareAndSet call accepts an int in the index position. Looking through the VarHandle APIs, nothing jumps out as obviously exposing a CAS operation against memory allocated using either the old sun.misc.Unsafe method or the new SegmentAllocater interface introduced in JEP 454/Java 22. Where is this functionality exposed, if anywhere?