Is it safe to call the Present() function from a non-ui thread

[shi-yan]

I know I can create command buffers using threads other than the main thread,

but can I submit the command buffer and call the present() function from non-ui threads ?

My previous experience with opengl tells me no. But I tried it on linux, it worked. Is it safe to do cross-platform wise?

[cwfitzgerald]

Yup, you can call it from any thread.

[shi-yan]

I have written a detailed description of the issue I saw

#2727

with a reproduce code.

[shi-yan]

so I did more investigation. I read the wgpu-hal code and noticed that Surface has a field "main_thread_id".

In the above code, I created the surface in a non-ui thread. So the "main_thread_id" isn't really the main thread's id.

I adjusted my code to create the Surface on the main thread, and things could render now.

[cwfitzgerald]

Interesting, that sounds like it should be part of the contract of create_surface. It makes sense condering the restrictions placed on windows.

[shi-yan]

if the raw Metal API doesn't have this restriction (it seems to be the case, as I remember), and this restriction comes from the WGPU layer, then I think this is a bug.

[cwfitzgerald]

Alright, could you update the issue description with this information?