[PyTorch] How to clone an instance of Module?

[guangster]

How do you subclass Cloneable when extending Module defined in Java? (Or more generally how to properly clone a class defined in Java that extends Module?)

For example, in the SimpleMNIST example I am trying to clone net. However if I try to clone the net object directly here:
https://github.com/bytedeco/javacpp-presets/blob/master/pytorch/samples/SimpleMNIST.java#L38
by calling net.clone() I will get an error:
clone() has not been implemented for torch::nn::Module. Subclass torch::nn::Cloneable<torch::nn::Module> instead of torch::nn::Module to inherit the ability to clone.

The docs here http://bytedeco.org/javacpp-presets/pytorch/apidocs/org/bytedeco/pytorch/Module.html says

...Attempting to call the clone() method inherited from the base Module class (the one documented here) will fail. To inherit an actual implementation of clone(), you must subclass Cloneable. ...

which is what I'm guessing I have to extend instead of just the base Module. I'm guessing this is torch::nn::Cloneable, and not the java.lang's Cloneable interface (I tried that and it did not work). I saw Javacpp has code like https://github.com/bytedeco/javacpp-presets/blob/master/pytorch/src/gen/java/org/bytedeco/pytorch/Conv1dImplCloneable.java#L18 which then produces specific cloneable components. Can we do something like that in Java directly on an object defined using JavaCPP (like net above)?

[saudet]

That's a class template, so we can't create new instances of that without a C++ compiler. The easiest way to go about something like this is to fork the presets and add what you need as new files in @Platform(include=..., along with an updated InfoMap, in a similar fashion to what @yukoba did in the case of LLVM here:
https://github.com/bytedeco/javacpp-presets/blob/master/llvm/src/main/resources/org/bytedeco/llvm/include/FullOptimization.h

@HGuillemet might have other ideas.

[guangster]

I see. Are there any other ways to clone Module then? We would want to be able to define networks in Java without having to write C++ code every time.

…

On Sep 15, 2022, at 5:47 PM, Samuel Audet ***@***.***> wrote:  That's a class template, so we can't create new instances of that without a C++ compiler. The easiest way to go about something like this is to fork the presets and add what you need as new files in @platform(include=..., along with an updated InfoMap, in a similar fashion to what @yukoba did in the case of LLVM here: https://github.com/bytedeco/javacpp-presets/blob/master/llvm/src/main/resources/org/bytedeco/llvm/include/FullOptimization.h @HGuillemet might have other ideas. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you authored the thread.

[saudet]

@sbrunk Any ideas?

[HGuillemet]

If you'd like to clone an instance of a Java class subclassing Module, you need a Java implementation of clone(), since the C++ library knows nothing about the Java subclass. We could define some CloneableModule mapping torch::nn::Cloneable<torch::nn::Module> and Java modules could inherit from it instead of Module. So the Java implementation of clone() could call the C++ clone() from Cloneable, but it won't help since you'll get an object that is not an instance of the Java class.

For saving/loading models, I currently use OutputArchive and Module.save/Module.load.
Maybe could you use it for cloning too ?

[guangster]

In the example, it looks like the c code has to implement virtual function like virtual void bar() { and in Java I have to use the annotation @Virtual. However since ReadFunction is already defined with its own c header etc... I can't really replicate the example in your link.
Instead I tried

        static class CloneWriter extends torch.WriteFunction {
            @Override
            @Virtual
            public native long call(Pointer buf, long nbytes);
        }

and then something like

CloneWriter cloneWriter = new CloneWriter() {
                public long call(Pointer buf, long nbytes) {
                   ...
                }
            };

however even before calling save_to(cloneWriter) I get a crash. I tried some other options like just directly overriding call but they all seem to result in crash. Am I missing something? Or does this mean I would have to modify the c ReadFunction definition?

[saudet]

It's probably just getting garbage collected prematurely. Try to keep a reference in a field.

[saudet]

Also try with a direct subclass of WriterFunction, a subsubclass might not work indeed.

[HGuillemet]

Have you seen my comment above about copying values between 2 existing instances of your model, instead of using archives ? I believe it's a simpler solution.

[guangster]

@HGuillemet Thank you, I ended up going with this suggestion and calling module.parameters(true) and module.buffers(true) to get each Tensors, then calling tensor.copy_(...) on them, it is working!

[saudet]

It's probably just getting garbage collected prematurely. Try to keep a reference in a field.