`load_folder` deadlocks when file watcher detects added/removed files

[amtep]

Bevy version and features

Tested with 0.18.1 and main branch (bb1d516).

I reproduced it with a modified asset_loading example, default features + dev (for the file watcher)

[Optional] Relevant system information

Rust 1.95.0

SystemInfo { os: "Linux (Debian GNU/Linux)", kernel: "6.19.8+deb14-amd64", cpu: "AMD Ryzen 7 5800X 8-Core Processor", core_count: "8", memory: "15.5 GiB" }

AdapterInfo { name: "AMD Radeon RX 7800 XT (RADV NAVI32)", vendor: 4098, device: 29822, device_type: DiscreteGpu, device_pci_bus_id: "0000:2d:00.0", driver: "radv", driver_info: "Mesa 26.0.2-1", backend: Vulkan, subgroup_min_size: 32, subgroup_max_size: 64, transient_saves_memory: false }

What you did

I modified the asset_loading example to reproduce the problem:

diff --git a/examples/asset/asset_loading.rs b/examples/asset/asset_loading.rs
index 49d2dca27..3d62b2787 100644
--- a/examples/asset/asset_loading.rs
+++ b/examples/asset/asset_loading.rs
@@ -2,6 +2,9 @@
 
 use bevy::{asset::LoadedFolder, prelude::*};
 
+#[derive(Resource)]
+struct FolderResource(Handle<LoadedFolder>);
+
 fn main() {
     App::new()
         .add_plugins(DefaultPlugins)
@@ -52,7 +55,8 @@ fn setup(
     // to load.
     // If you want to keep the assets in the folder alive, make sure you store the returned handle
     // somewhere.
-    let _loaded_folder: Handle<LoadedFolder> = asset_server.load_folder("models/torus");
+    let loaded_folder: Handle<LoadedFolder> = asset_server.load_folder("models/torus");
+    commands.insert_resource(FolderResource(loaded_folder));
 
     // If you want a handle to a specific asset in a loaded folder, the easiest way to get one is to call load.
     // It will _not_ be loaded a second time.

Then I ran cargo run -F dev --example asset_loading and waited for the window to load, then ran touch assets/models/torus/testing.gltf to trigger a reload.

What went wrong

The game printed 2026-04-23T17:53:13.609789Z INFO bevy_asset::server: Reloading folder models/torus because the content has changed and then stopped responding to input. Even hitting the close button on the window frame led to a pause, then my window manager offering to kill the process.

(Well, the example doesn't accept input anyway. Hitting the close button is how I verified it had the same problem as my game.)

Additional information

I traced the execution to this line, which is where it stops:

crates/bevy_asset/src/server/mod.rs:
self.write_infos().stats.started_load_tasks += 1;

in load_folder_internal.

It's called from handle_internal_asset_events, which already holds the lock to infos.

[amtep]

Btw I first encountered this problem when merely editing files, not adding/removing, because my editor saves files by first moving the old one out of the way and then writing a new one. So it looks like a new file, and the game hangs.

My co-developer uses a different editor and did not see this effect, which caused some initial confusion.

[andriyDev]

Yup, you're quite right. It looks like what is happening is that at the top of handle_internal_asset_event we take the lock, and then when we call load_folder_internal (immediately), we get deadlocked. Thanks for your tracking, it was spot on!

I think we should just pull the same trick we do for regular loads: just defer it until after the source event handling.