Asset loading depends on the "multi-threaded" feature being enabled

[komadori]

Bevy version

5d110eb (0.12-dev)

Relevant system information

AdapterInfo { name: "NVIDIA GeForce 940MX", vendor: 4318, device: 4941, device_type: DiscreteGpu, driver: "NVIDIA", driver_info: "535.113.01", backend: Vulkan }
SystemInfo { os: "Linux 21.2 Linux Mint", kernel: "5.15.0-86-generic", cpu: "Intel(R) Core(TM) i7-7820HQ CPU @ 2.90GHz", core_count: "4", memory: "31.2 GiB"

What you did

Run the animated_fox example using a subset of Bevy's default features that was sufficient with the previous release (0.11).

cargo run --release --example animated_fox --no-default-features --features="animation,bevy_asset,bevy_scene,bevy_winit,bevy_core_pipeline,bevy_pbr,bevy_gltf,bevy_render,ktx2,zstd,png,x11,tonemapping_luts"

What went wrong

The fox asset is not displayed at all, only the background.

However, if I add the "multi-threaded" feature then the example works correctly. Is it intentional that this feature is required for asset loading to work?

[alice-i-cecile]

I suspect this is a general problem of asset loading currently. This code should fail to compile if it doesn't run.

That said, I think I'd prefer to enable single-threaded asset loading.

[robojeb]

I spent some time on my lunch. and it seems like there is something racy going on between the async-fs IO executor and the single threaded local executor bevy is using.

Async code isn't my forte so I am not entirely sure where the mismatch is, but if I set a breakpoint on raw.rs:644 inside async-task (v4.5.0) and I step through slowly, eventually the asset loads.
But if I step through quickly, I get an AssetEvent::Added event, but eventually the LocalExecutor has no more items in its queue and so no more progress is made on actually loading the asset.
It always seems to happen when going through an async-fs future.

[rparrett]

I was just hit by this while migrating an app that used only a subset of Bevy's default features.

The symptoms were that my assets were in a perpetual LoadState::Loading. This was a very confusing situation.

edit: To clarify, my app doesn't need single-threaded asset loading. All I needed to do was add the multi-threaded feature and I was good to go. If single-threaded asset loading worked I would probably just be confused about why my app was no longer multi-threaded, if I even noticed.