Pyodide fatal error occurs in Pyxel on WASM

[kitao]

When Pyxel is running on Web, Pyodide reports a fatal error.

As far as I have investigated:

• SDL2 on Emscripten throw 'unwind' exception when emscripten_set_main_loop is called. It's intentional. The purpose of it is to stop current code and continue infinite loop.
• Pyodide catch every exception and report it as 'fatal error', and then throw it again.
• As the result of that, Pyodide reports a fatal error when SDL2 started.

I will continue to investigate, but please let me know if there is a good solution.
One idea is to stop print fatal_error from Pyodide when the exception name is 'unwind' .

[kitao]

@km19809 @laurentabbal

[kitao]

Other idea is set the simulate_infinite_loop argument of emscripten_set_main_loop to false and handle infinite loop in Rust side though I'm not sure it is possible or not.

https://emscripten.org/docs/api_reference/emscripten.h.html

[km19809]

Ok. As you mentioned, throwing an exception is intentional.
But the problem is, it is a Javascript Exception.
It can be handled neither by the rust side (It would not pass to the rust side) nor by the pyodide side (We need to modify it).
So I think simulate_infinite_loop = false is admirable.
Then the problem is the rust loop.
With the loop, it may block the browser (or may not. it should run the main loop asynchronously.).
Without the loop, it will terminate function and release variables (including VM).

So I will try simulate_infinite_loop = false and find ways to safely terminate the game loop.

[kitao]

@km19809 I agree with you. simulate_infinite_loop = false looks good from the viewpoint of Pyodide execution.

In that case, the point is how to sleep for long time after emscripten_set_main_loop in Rust, I think.

I checked Emterpreter feature of Emscripten. It may be possible to realize sleep but its overhead is large.
I also read some article in which the author tried to run VIM on web.
He executed VIM in web worker and used Atomics.wait as sleep.
So if Pyxel and Pyodide executed in web worker and call Atomics.wait via emscripten_run_script. "Infinite sleep" can be realized.

This is my current hypothesis.

[kitao]

Not the best solution, but I suppressed the uncaught exception error for an intentional 'unwind' exception from Emscripten by modifying Pyodide for now.

[km19809]

I tested simulate_infinite_loop = false but it did not work as expected. It is hard to "sleep" yet.
I also tried emscripten_request_animation_frame_loop but the compiled code cannot find the signature of the function.
I cannot find why, but emscripten_request_animation_loop is not available now.
I am still investigating, but for now, modifying pyodide to ignore 'unwind' is the best solution.

[kitao]

OK. Error itself is prevented now. So let me close this issue.
If there's any progress, let's open new issue.