Java 25 - Warnings for Unsafe

[purbarunc]

I am getting the below warnings when starting up EHCache 3.11.1 with Java 25. Seems these are related to Unsafe which is deprecated in Java 25 and set for removal in future.

[skin27]

Same warning after upgrading to Java 25 ( 3.11.1):

WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by org.ehcache.impl.internal.concurrent.ThreadLocalRandomUtil (file:/C:/Users/user/.gradle/caches/modules-2/files-2.1/org.ehcache/ehcache/3.11.1/5f68a40207555a7059bf864116da3dfae89a49c1/ehcache-3.11.1.jar)
WARNING: Please consider reporting this to the maintainers of class org.ehcache.impl.internal.concurrent.ThreadLocalRandomUtil
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release

[rivancic]

The problematic code is at:
https://github.com/ehcache/ehcache3/blob/master/ehcache-impl/src/unsafe/java/org/ehcache/impl/internal/concurrent/ThreadLocalRandomUtil.java#L44

This line uses the deprecated Unsafe.objectFieldOffset() method which triggers:
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by org.ehcache.impl.internal.concurrent.ThreadLocalRandomUtil

Potential solution with using MethodHandles, while as its relying on a Java Thread class internals would require for the consumer to add --add-opens flags to the app.

[ydrozhdzhal]

Same issue with 3.12.0

[Shaquarib]

What I would do
I would not immediately suppress the warning.

First determine the caller:

java -version

and inspect your dependency tree:

Maven

mvn dependency:tree | grep -i -E 'ehcache|terracotta|bytebuddy'

Gradle

./gradlew dependencies | grep -i -E 'ehcache|terracotta|bytebuddy'

Then check whether there is a newer Ehcache/dependency version that eliminates the Unsafe call.

For Java 25 specifically, the warning is intentional: Oracle recommends treating Java 25+ migrations as a reason to identify and eliminate dependencies on these Unsafe methods rather than assuming they will remain available indefinitely.
O
Oracle Docs

Temporary workaround
If the application otherwise works correctly, Java provides a compatibility option to allow these calls without the new warning:

--sun-misc-unsafe-memory-access=allow

However, I'd regard that as a temporary compatibility measure, not the long-term solution. The underlying Unsafe memory-access methods are on the removal path.
O
OpenJDK

So the practical path is:

Java 25 → warning → identify caller → upgrade/replace offending library → eventually remove Unsafe dependency.

[thomass4t]

@ydrozhdzhal
As @rivancic already mentioned, the problem is in the class ThreadLocalRandomUtil and there is no newer ehcache version without this warning.

EHCache comes with a customized ConcurrentHashMap which is optimized for speed. The customized ConcurrentHashMap uses ThreadLocalRandomUtil to get a random seed / slot per Thread.

[ydrozhdzhal]

@thomass4t this is clear, but are there plans to get rid of this ThreadLocalRandomUtil ? Because in newer JDK versions it can be removed and it would be not possible to use ehcache library.

[HoffmannTom]

@ydrozhdzhal
The only information and references I found are:
#3297
#3151
Maybe someone has the ability and is willing to contribute and create a PR.
The code frequency is not high though: https://github.com/ehcache/ehcache3/graphs/code-frequency