How to access Resource in an async task?

[feelingsonice]

I have a procedural generation task that may take a long time to complete so I've create a plugin to listen for an Event trigger. The task requires access to certain Resource stored as either an Asset resource or plain Resource. This means I only have borrowed access to it AFAIK since Bevy stores and owns it.

I'd really rather not clone this Resource. Ideally, this event listener is able retrieve some sort of reference to it, pass it to the async task (I'm using AsyncComputeTaskPool), and that's it. However, I can't send the Res via the Event as there's lifetime issues, and I'm also not seeing a easy way to pass it into the async task.

Anyone have suggestions?

[TimJentzsch]

The only safe way to do this that I can think of is to wrap the contents of your Resource in an Arc<Mutex<T>>.
The Arc can be cheaply cloned (without cloning T) and the Mutex ensures that the async task and the Bevy systems cannot access T at the same time.
Otherwise you could easily run into memory issues.

Just keep in mind that a Mutex of course adds overhead which might slow down your app, depending on your use cases.

[feelingsonice]

I'm planning to just put it behind arc and skip the Mutex since I don't need to mutate this at all. You think that'd work?

[nicopap]

The downside is that you won't be able to mutate the resource as long as an async task is running, though you can still read it. You can use Arc::get_mut if the Arc inside the resource is truly the last reference existing.