Research .NET runtime WASM module lifecycle

[elringus]

It is not clear whether the .NET runtime WASM module have to be terminated and/or if it can be re-initialized.

There appears to be emscripten_force_exit function in the module, but it throws an error: https://github.com/Elringus/DotNetJS/blob/97647de97a9ffe0aafdc1941a947f79f9816b9d8/JavaScript/dotnet-runtime/src/wasm.ts#L25

Is someone have any related info, please let us know here.

[Aloento]

WASM that is not in use should be destroyed. If not, the Mono VM will always be running in the background. EmscriptenModule cannot be reused, so a MONO VM cannot be reinitialized after it is created. However, you can create a new EmscriptenModule.

In my project: https://github.com/Aloento/FFmpeg4JS/blob/02832f0c5765d78b3d0125e7698516bbd75b433b/src/ffmpeg.js#L5230 https://github.com/Aloento/FFmpeg4JS/blob/02832f0c5765d78b3d0125e7698516bbd75b433b/src/ffmpeg.js#L390

I usually let WASM run in the worker, it's simpler, you just need worker.terminate();

[elringus]

WASM that is not in use should be destroyed.

Yeah, I felt that way as well, but as mentioned it throws an error on exit. Maybe something on the mono side.

[Aloento]

You can try to call function exitRuntime() in your env like: https://github.com/Aloento/FFmpeg4JS/blob/02832f0c5765d78b3d0125e7698516bbd75b433b/src/ffmpeg.js#L1047

Or could you share the detail for this error?

[elringus]

I've tried it again, but looks like emscripten_force_exit has been removed since I've last tested this. Not sure what's the correct way to shutdown/dispose the mono runtime now.

[Aloento]

I don't think you need to close MONO, but to exit EmscriptenModule. Just exit the EmscriptenModule then MONO will dispose too.

[elringus]

Given emscripten_force_exit is not exported, mono is probably built without the exit flag. Not sure if it's possible to terminate by other means. https://emscripten.org/docs/api_reference/emscripten.h.html#c.emscripten_force_exit

[Aloento]

It's easy to export like: https://github.com/Aloento/FFmpeg4JS/blob/02832f0c5765d78b3d0125e7698516bbd75b433b/src/ffmpeg.js#L5123

eg: Module["exitRuntime"] = exitRuntime;

[elringus]

Right, so it's actually built with no exit flag: https://github.com/Elringus/DotNetUMD/blob/6807d5ceeb52f9421802985d3737479406c95b08/src/mono/wasm/wasm.proj#L67

Guess that means it can't be directly disposed. We could override the flag in our custom branch, but due to #20 I want to refrain from further patches. Maybe they'll change it in .NET 7.

[Aloento]

Blazor certainly doesn't exit, as it runs through the entire page lifecycle and will not change in future versions I think. So you're better off building a version yourself.

[elringus]

It's .NET runtime for wasm, which is not just for blazor, so there's still a chance. They've already made a lot of progress to modularize it in .NET 6-7. And again, I'm planning to opt-out of custom runtime build by .NET 7 release, so patching it further is not desired.