Temporary fix to prevent panics on loading Gltf assets in parallel due to stack overlows

[john-sharratt]

Objective

Temporary fix for
#15271

Solution

Disables the inline invocation of the task engine after loading a Gltf as the blocking call is causing task engine re-entrance and stack overflow

Testing

Tested on my local branch which is a fork, not directly tested on the issue raiser.
Further testing would be required before accepting this however this does fix my issue

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[alice-i-cecile]

Can you say more about why this fixes the issue observed?

Note that we won't merge commented out code, but let's work on getting the fix nice before working on polish.

[john-sharratt]

Yeah no worries, this is mainly just to help out victor if he can't wait for a proper patch.

Basically the bug is because blocking code is running within async code which is generally a bit of an anti-pattern, what tokio and others do is shift blocking code to a dedicated blocking thread pool so edge cases like this don't happen.

Ultimately you could fix this and make it work but its not really deterministic or easy to rationalize. Better would be to make sure all your blocking code and async code run on different thread pools.

[john-sharratt]

Here's some background information you can read up on blocking inside async contexts

https://docs.rs/tokio/latest/tokio/task/fn.block_in_place.html
https://tokio.rs/tokio/topics/bridging
https://ryhl.io/blog/async-what-is-blocking/

[john-sharratt]

B.t.w. Now we are talking a bit more in actively and given we're on the topic of task management - I've solved the multi-threading problem in WASM running in the main browsers for other projects if you want some tips.

[alice-i-cecile]

@john-sharratt notes over in #4078 would be hugely appreciated!