rebooting OpenJDK mobile

Johan Vos johan.vos at
Fri Jun 28 14:09:08 UTC 2019


After a long time, it is a good moment now to restart the public work in
the OpenJDK Mobile project.
In the past, we had a repository with code based on OpenJDK 9 that allows
to build the class libraries (including native code) and one or more VM's,
for Android and iOS.

While this works, we still have the limitation on iOS where dynamic code is
not allowed, hence a JIT is not an option. The Zero VM works there
(interpreter mode) but is slow.

Today, we can use the GraalVM AOT compiler to compile the code at build
time. We can link the compiled Java code with native libraries compiled for
the target OS, and create executables. Most of the VM functionality is
provided by a very small set of files in SubstrateVM (linked to by GraalVM
native image)

We already did this for iOS, based on Java 11 (see and JavaFX 13.
(see our announcement at  The
diff to the upstream code is remarkably small.

It is my goal now to use project Skara to create a synchronized fork of the
OpenJDK master, and to push the changes required to build the native libs
for the core libraries in there.
Ultimately, it would be ideal if all required changes can go upstream.

At this moment, this is iOS only, but there are no showstoppers to do this
for Android as well. The architectures are pretty similar.

- Johan

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