JEP draft: Prepare to Restrict The Use of JNI

[Ron Pressler]

Hi.

JNI has been part of the Java Platform since JDK 1.1, but it is inherently
unsafe, so we are proposing to restrict the use of JNI in line with the use of
restricted methods in the Foreign Function & Memory (FFM) API [1].

The FFM API, expected to become permanent in JDK 22, has methods for interacting
with native code that are inherently unsafe. To protect the integrity of the
Java Platform [2], use of these methods is restricted. This means that calling
them causes warnings, unless the user enables unsafe native access on the
command line. In a future release, calling them will cause exceptions instead
of warnings.

We propose to align JNI and FFM as follows. Starting in JDK 22, the Java runtime
will give warnings about the use of JNI, unless the user (as for FFM) enables
unsafe native access on the command line. In a future release, using JNI will
cause exceptions instead of warnings.

In other words, our proposal is: In the future, code that uses JNI will run only
if unsafe native access is enabled, and to prepare for that future, JDK 22
should spotlight the use of JNI with warnings. We've published a draft JEP that
explains why using JNI is unsafe and describes the warnings [3].

We recognize that many applications use JNI and will be impacted by this
proposal. It is bound to spark discussion that continues even after the
preparatory warnings in JDK 22. Comments are welcome.

— Ron

[1]: https://openjdk.org/jeps/442
[2]: https://openjdk.org/jeps/8305968
[3]: https://openjdk.org/jeps/8307341