WASM (without Blazor) is very slow for large number arrays

I'm trying to use my c# code in my JavaScript by publishing the c# code as webassembly. It works for the most part, except for large number arrays.

In my c# code, I have a simple method like this:

        [JSInvokable]
        public static double[] Test(double[] a, double[] b)
        {
            return new double[];
        }

then I publish the js and in my JavaScript, I call the method:

var temp = dotnet.MyTest.test(a, b);

where a and b are number arrays. Each has 1 million elements.

It took about 40 seconds for temp to get the return value. A direct c# call to the same test method would return immediately.

Am I missing anything?

When passing a double[] from Javascript to WASM.

We need to do something called marshalling of the data.

In this case, the default behavior for marshalling of a JS array into a double[] is to copy the array.

That is pretty slow.

The only way I know that might be possible for you to achieve fast interop with huge arrays of Number, would be for you to:

• Pre allocate a large array from dotnet.
• Pin the array
• Pass the memory address from dotnet to JS
• Wrap the wrap the address + size in a DataView (using the WASM memory object)
• Write to the DataView
• Call the DotNet method using offsets and size pointers, and construct Span<double>
• Profit