GraalVM + Nashorn Cannot extend classes

Question

I'm attempting to use graal + nashorn interop to write nodejs that interacts with Java. I'm starting graal with node --jvm --jvm.Xss2m --jvm.Dtruffle.js.NashornJavaInterop=true --jvm.classpath=libs/ --polyglot app.js. I cannot extend a class though. The javascript code is

const GraaljsgrpcServiceImpl = Java.type('com.thing.GraaljsgrpcServiceImpl');
const HelloReply = Java.type('com.thing.HelloReply');
var GrpcImpl = Java.extend(GraaljsgrpcServiceImpl, {
    sayHello: function(request, responseObserver) {
        responseObserver.onNext(HelloReply.newBuilder().setMessage("Hello " + request.getName()).build());
        responseObserver.onCompleted();
    }
});

and my error is TypeError: Could not determine a class loader with access to the JS engine and class com.thing.GraaljsgrpcServiceImpl This seems to point to a classloader issue with the java code I'm referencing and where the javascript is running(i.e. 2 different classloaders). Is there a way to pull this off when using graal/nodejs?

Answer 1

Thanks for reporting this classloader problem. We are looking into that and should be able to fix that with our next release (0.32 expected early March).

Regarding the --jvm.Dtruffle.js.NashornJavaInterop=true flag: we strongly encourage not using that, but depending on the built-in interoperability of GraalVM. However, in this mode Graal.js is not 100% compatible with Nashorn/Rhino; for instance, we are not supporting Java.extend in that mode. Is Java.extend the only reason why you set the NashornJavaInterop flag?

Thanks, Christian