Does toga support multiprocessing?

[Jzhenli]

Hi, I use the multiprocessing in toga app for some heavy cpu loading tasks, it can run well with "briefcase dev", but when use the "briefcase run" will open multiple instances of the app, is this a bug? if yes, how to fix it? BTW, my system OS is win11.

[freakboy3742]

As noted in this ticket, multiprocessing isn't currently possible.

[Jzhenli]

@freakboy3742 Seems the windows platform use multiprocessing as spawn mode, and the stub not support it. Now I want to know if the android platform support multiprocessing? Android based on linux and the multiprocessing may be default as fork mode, right?

[freakboy3742]

No. Android and iOS both prohibit the use of fork and spawn. Although they are both "unix-like" operating systems, their process model largely assumes that the app is a single process, running in the foreground. Calls to fork/spawn will either fail, or cause lockups in the app.

[Jzhenli]

I originally wanted to use this solution: togo webview as ui, and create a process to run fastapi as a background server, then packaged them as an android app, so it's not possible now. Would u have any suggestion for integrate toga webview and fastapi web server? @freakboy3742

[freakboy3742]

You use threads, not processes. This is what the positron-static and positron-django examples do to achieve exactly what you've described - a web view-based GUI backed by a web server on the same app.

I haven't got a "ready to use" example for FastAPI - but the general approach should be exactly the same.

[Jzhenli]

FastAPI is primarily an ASGI framework, and the two examples you offered are WSGI framework, they have some differences, I don't know how to stop ASGI in the thread.

[freakboy3742]

You'll need to take that up with the FastAPI folks. I've never used FastAPI, so I can't advise on how to run a FastAPI server.

However, if there's an async end point that you can await that runs a server, you may not need a thread at all - you may be able to use asyncio.create_task() to install the async handler directly into the Toga app's GUI event loop.