Lessons from Mixing Rust and Java: Fast, Safe, and Practical

never_inline

1. The article seems kind-of shallow. I didn't see any concrete (qualitative or quantitative) remarks about the "fast" part. I don't doubt you have reasons to do this - but I expected some information on what component are you writing using Rust + JNI, and how it helped? Or is it just a demo?

At some point, repeated calls into the JNI are counter-productive to performance, since the JIT can not optimize them. Pinning affecting garbage collection is another potential drawback if any of your rust calls are long lived. If we don't measure and just conclude "we are fast because rust is faster than Java, and we took average of both speeds", it's a disservice.

2. Also, I see unsafe for each call? I'd rather isolate this into a class / different file, since in JNI only few types of calls are possible. (method returning one of the primtive types, an object or `void`). This is the approach I took in dart jnigen. (Though there, the call is Dart -> Java, not Java -> Native language).

    unsafe {
      env.call_method_unchecked(
                java_logger,
                logger_method,
                ReturnType::Primitive(Primitive::Void),
                &[JValue::from(format_msg(record)).as_jni()]
      );
    }

3. I believe some details are missing here. What's native_add_one mapped to? And how is tokio futures awaited from Java? I believe that's the important part you should be presenting.

    public CompletableFuture<Integer> add_one(int x) {
        long futureId = native_add_one(x); // Call Rust
        return AsyncRegistry.take(futureId); // Get CompletableFuture
    }

4. Also please don't use ChatGPT for writing anything. It totally derails the reader by mentioning irrelevant details and long winded corporate conclusion at the end of every sentence.

killme2008

This article summarizes our experience from a commercial project that runs on an in-vehicle Android system. In this project, we needed to invoke Rust code(DB) from Java(App), so we couldn't directly use the project’s source code for demonstration. Instead, we created a demo project: https://github.com/GreptimeTeam/rust-java-demo

1. I agree that using Rust doesn't necessarily mean faster performance; it simply gives you the opportunity to implement some compute-intensive modules in Rust, which is a possible approach.

2. This is a great suggestion, and we organized our project in the same way. You don’t need to use unsafe for every call. However, if you want to call JNI APIs from Rust, unsafe is required.

3. Sorry, some details were missing here. We use AsyncRegistry(Java) as an intermediary. Before initiating an async operation in Rust, we need to call Java code in advance to register a future and obtain a unique future ID. After the async execution completes, we retrieve the registered future by its ID, and then complete it or complete it exceptionally depending on the async result. You can refer to this code: https://github.com/GreptimeTeam/rust-java-demo/blob/90ffa0ba... and https://github.com/GreptimeTeam/rust-java-demo/blob/90ffa0ba...

4. This article was not generated by AI; it’s just that our official blog has a fixed template at the end. Sorry for the inconvenience.

lukax

Do not write the bindings manually. Just use the amazing uniffi-rs library from Mozilla.

https://github.com/mozilla/uniffi-rs

You can generate bindings for multiple languages. It supports error handling on both sides and latest versions also support native async integration.

I've used it to reuse the same Rust engine in iOS and Android apps and write native UI.

https://github.com/koofr/vault

cadamsdotcom

Thanks! Anywhere you hit issues?

rusbus

Another useful library in this space that allows you to avoid manually writing bindings is https://github.com/duchess-rs/duchess

bullen

I agree that Java + native is the way to go.

But does rust really give you an edge over C/C++?

Here is how you do JNI with C++: http://move.rupy.se/file/jvm.txt

So simple it's ridiculous!

Then you can use RegisterNatives to give C++ API to the Java side instead of the stub (Java calls C++ .dll/.so) thing...

invalidname

Why didn't OP use Panama or the modern Java native APIs which are far better than JNI?

null

[deleted]

cyberax

Android?

pjmlp

Proving the point about Android being Google's J++, and Kotlin their C#.

invalidname

Does OP target Android?

sgt

Should be possible with Zig as well. Is this one up to date? https://github.com/zig-java/jui

HN

Lessons from Mixing Rust and Java: Fast, Safe, and Practical

Lessons from Mixing Rust and Java: Fast, Safe, and Practical