Using sun.misc.Unsafe in Java 9

The Java 9 EA version is out and we can now see how to use sun.misc.Unsafe. I led the public campaign to retain access to it in Java 9, which was ultimately successful, leading to the amendments to JEP 260.

So, how did things end up?

Getting Set Up

First, you need to download Java 9 EA. For an IDE, I use IntelliJ IDEA. You need the new 2017.1 Public Preview, which came out 27 February 2017. Earlier versions don’t work with Java 9.

The JDK.Unsupported Module

Sun.misc.Unsafe is now available in the jdk.unsupported module. This module is present in the full JRE and JDK images.

Here is the module declaration for jdk.unsupported:

module jdk.unsupported {
    exports sun.misc;
    exports sun.reflect;
    exports com.sun.nio.file;

    opens sun.misc;
    opens sun.reflect;
}

As you can see, sun.misc is exported.

Using It

I have a sample project with a package java9unsafe and a module with the same name.

To use Unsafe, you need to add jdk.unsupported to your code’s module declaration:

module java9unsafe {
    requires jdk.unsupported;
}

Fortunately, IDEA will detect the declaration if missing and suggest adding it for you when you hover over your import statement.

Then you can use Unsafe. Note you have to indirectly get at the Unsafe instance via reflection otherwise you get a security exception.

module jdk.unsupported {

public class Java9Unsafe {

    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        System.out.println("The address size is: " + getUnsafe().addressSize());
    }

    @SuppressWarnings("restriction")
    private static Unsafe getUnsafe() throws NoSuchFieldException, IllegalAccessException {
        Field singleoneInstanceField = Unsafe.class.getDeclaredField("theUnsafe");
        singleoneInstanceField.setAccessible(true);
        return (Unsafe) singleoneInstanceField.get(null);
    }

}

And the answer: The address size is: 8.