On iOS, loading many assets in `AssetMode::Processed` causes some assets to fail to load

[Seldom-SE]

Bevy version

0.14.0

Relevant system information

iOS 17.5.1

What you did

Loaded 128 images all at once with AssetMode::Processed in iOS. The images aren't preprocessed, they're just configured to be copied into imported_assets.

What went wrong

5 of the assets failed to load with �[2m2024-07-30T19:31:05.814567Z�[0m �[31mERROR�[0m �[2mbevy_asset::server�[0m�[2m:�[0m Encountered an I/O error while loading asset: Too many open files (os error 24).

Additional information

I tracked the loading states of the asset with logging:

�[2m2024-07-30T19:31:33.444959Z�[0m �[32m INFO�[0m �[2mbevy_mobile_example�[0m�[2m:�[0m == LOAD STATES ==
�[2m2024-07-30T19:31:33.444966Z�[0m �[32m INFO�[0m �[2mbevy_mobile_example�[0m�[2m:�[0m no_state   0
�[2m2024-07-30T19:31:33.444970Z�[0m �[32m INFO�[0m �[2mbevy_mobile_example�[0m�[2m:�[0m not_loaded 0
�[2m2024-07-30T19:31:33.444975Z�[0m �[32m INFO�[0m �[2mbevy_mobile_example�[0m�[2m:�[0m loading    0
�[2m2024-07-30T19:31:33.444980Z�[0m �[32m INFO�[0m �[2mbevy_mobile_example�[0m�[2m:�[0m loaded     123
�[2m2024-07-30T19:31:33.444984Z�[0m �[32m INFO�[0m �[2mbevy_mobile_example�[0m�[2m:�[0m failed     5

This issue doesn't occur in AssetMode::Unprocessed with 512 images. I haven't tested with more than that. I suspect there's already a mechanism in Bevy that prevents too many assets from loading all at once, but it doesn't take into account .meta files.

Behold, a repro: https://github.com/Seldom-SE/testetst/blob/279fa27a26bf0b845a5558a815c1f8d031c26fa2/src/lib.rs It's based on bevy_mobile_example. To run it:

1. Make sure you're on the linked commit
2. ./copy_assets.sh. This just copies the one image 127 times.
3. cargo run --features preprocess
4. Configure the Xcode project to use your certificate. It might just do this automatically.
5. Run from Xcode (or with the Makefile, but I haven't tested that)

[Seldom-SE]

Currently working around it by loading our assets in two different states

[Braymatter]

Confirming this is still an issue in 0.15.1

Interestingly seems to be somehow related to the file_watcher feature, as having file_watch enabled reproduces the issue, but disabling it makes the app load fine.

[Braymatter]

Adding this should fix it:
#11349

[mockersf]

#11349 doesn't really fix this, it hides the issue. Avoiding failures by delaying opening files is still a better solution