Window.events blocks all other events

[chirsz-ever]

example code:

import {
    EventType,
    WindowBuilder,
    getKeyName
} from "jsr:@divy/[email protected]";

const win = new WindowBuilder("Three.js demo - webgpu/backdrop", 800, 600).build();

new Promise((resolve) => setTimeout(() => {
    console.log("timeout");
    resolve(undefined);
}, 1000));

for await (const event of win.events()) {
    if (event.type === EventType.Quit) break;
    else if (event.type !== EventType.Draw) continue;

    // FIXME: deno_sdl2 UI events would block network events?
    // await new Promise((resolve) => setTimeout(resolve, 1));
}

"timeout" would not be logged until the window close, or add the commented await line.

[littledivy]

win.events() returns a synchronous iterator that blocks the event loop until a new SDL event happens. Platforms like macOS assume GUI thread is the main thread.

There are a few ways to work around this:

• Allow users to wakeup SDL. I do somethink like this in wgui: https://github.com/littledivy/wgui/blob/a599923f4887af4b1da002de29e7cce6aeccabb9/app.ts#L103-L109
  When creating a promise, users add it to app.addTask(promise) and the event loop will run using setTimeout until the task completes.

• Move user code to a WebWorker thread so promises and microtasks are not blocked. This is probably the way to go.

[littledivy]

Another workaround is to use win.events(false) which will use SDL_PollEvent instead of WaitEvent and run the background tasks. Downside being that CPU will be busy when there is no work to do

[chirsz-ever]

I noticed the wait argument. Do you have any idea to make SDL_WaitEvent work with tokio? SDL_WaitEvent would block the thread until get an event. the SDL2 implementation looks like just polling until an event comes.

Maybe just await new Promise((resolve) => queueMicrotask(resolve)); before yeild anything?