JNA Catching Exceptions

Question

I have a quick question about dealing with exceptions being thrown by libraries under JNA...

When I throw an exception in the underlying native code, JNA gets a invalid memory access error. I'm assuming this is because C libraries cannot throw an exception up through it's stack (it's actually C++/CLR but has C exports)? So is there no real way to report the exception to Java? Or "should it work" and I'm just doing something incredibly wrong?

DllExport void Initialize(char* dir)
{
    throw gcnew System::Exception("Testing");
}

It would be nice for Java to be able to detect these thrown exceptions, and I guess I could actually look into passing a memory pointer into all my C exports and check to see if those are null or not, but seems like a roundabout way.

Answer 1

C++ exceptions can only be handled in C++ code. They should never be allowed to escape the C++ world (i.e., a C interface of C++ code should never let exceptions propagate). It is not even safe to let a C++ exception propagate through a layer of C code between two C++ modules (e.g., when a C++ function calls a C function which in turn calls a C++ function).

One of the reasons for this is that there is no standard on how C++ exceptions should be implemented, so C++ modules are only binary-compatible if compiled by the same compiler (in the same version). So code in any other language can't be set up to handle C++ exceptions.

In this case (C++ library, C interface, called from Java) you would have to catch the C++ exception, propagate the information through the C interface (e.g., by using error return codes), check for it in Java and throw an exception there.

Answer 2

You need to handle the c++ exception yourself and instead build a java exception which can be passed to the java side of the code.