rust-bindgen VS JNA

Rust supports two kinds of FFI: calling into Rust from another language; and calling into another language from Rust. Most of the thought and tooling that exists right now is organized around the second kind. For example, bindgen is a popular tool that generates useful Rust wrappers from a C or C++ header file.

I have looked into bindgen, but found that it would not be feasible due to OMPL not having a C API, just C++.

Yes! Are you running LLVM version 16.0.0 or newer, by any chance? I believe this is an issue with some builds of bindgen with newer versions of LLVM. See https://github.com/rust-lang/rust-bindgen/issues/2488

On native, you have to define a C API, probably using a header file. Even if both sides are implemented in Rust, they have to speak that C API (documentation).

Bindgen has some functionality for direct talk to C++ https://github.com/rust-lang/rust-bindgen

I am trying to use rust-bindgen (https://github.com/rust-lang/rust-bindgen) to link a static C library (say `libexample.a`) which is compiled in a separate project with CMake. The `libexample.a` depends on other libraries (for example `libcurl.a`) installed on the system.

It looks like the guy you're replying too was kind of an ass, but I do want to point out for anyone else reading that that's not actually that much of a technical limitation: rust code can natively call C code. The main thing you need is a translation of the C library's header file so rustc knows what C functions and structs exist, and that can be automatically generated with bindgen.

It's quite the different approach, but you could consider using bindgen instead.

Use bindgen or CXX to create Rust bindings for the C or C++ libraries.

As far as I understand it, with JNA, all calls into C code go through libffi: https://github.com/java-native-access/jna/blob/master/www/Fu...

This means that every call sets up some libffi data structures and libffi uses this information to perform the native call. Likewise in the other direction for return values. With JNI (and Panama), Hotspot can directly emit the argument/return code a the call, not too dissimilar from what a C or C++ compiler would do. There is still some overhead from maintaining JVM invariants. For example, I think a thread blocked in an FFI call can still participate in a safepoint. But that applies to JNI as well.

If you were prepared to go to the JVM you might try JNA. https://github.com/java-native-access/jna

Other good example, but for Java platform is JNA library. Do not mix it with Java's JNI, which is a bad example of how it could be done.

In case you haven't used it (assuming that you already know about JNI, for comparison) - https://github.com/java-native-access/jna is about as easy as it gets for native interop. Also, as mentioned in another comment, with the Java FFM (Foreign Function and Memory) API already in preview mode, pretty soon, there will be no external dependencies at all, and Java should be able to interop with any language that can talk to C.

The complexity of JNI has given rise to some community-driven libraries that make it simpler to do FFI in Java. Java Native Access (JNA) is one of them. It's built on top of JNI and at least makes FFI easier to use, especially as it removes the need to write any C binding code manually and reduces the chances of memory safety issues. Still, it has some of the disadvantages of being JNI-based and is slightly slower than JNI in many cases. However, JNA is widely used and battle-tested, so definitely a better option than using JNI directly.

This is about calling into any native operating system APIs, as long as they are callable via C or C++ (which these days means "all" operating system APIs).

JNI is somewhat harder to use, because you need custom glue on both sides of the border: Some custom classes in Java and some custom code on the C (and C++) side.

This proposal would remove the need for the glue on the C side and would allow a pure java solution.

Something like this has existed in third-party form for a while as JNA (https://github.com/java-native-access/jna), but now it's going to be built into the JRE itself (if the proposal passes through review)

I use JNA https://github.com/java-native-access/jna , as you can write the entire interface in Java faster as well as easier without the need of messing with the complexities of JNI.