Untity Synchronization context + Task.Run huge performance hit!

[RaventurnPatrick]

@marcospgp

@RaventurnPatrick Why do you use Task.Factory.StartNew() inside Task.Run()?

Does code inside a Task.Run() run under Unity’s SynchronizationContext or under the default one?

I’m trying to make sure my async/await code runs on more than one thread.

Bonus question: How to make sure all exceptions get logged, including when thrown inside methods returning either Task or void? Unawaited calls to Task returning methods have exceptions swallowed, as well as exceptions thrown in public Task Start() and other Unity callbacks declared as returning Task.

Code in the Task.Run runs under unity synchronization context for the first call (line 16).
After line 21 (SynchronizationContext.SetSynchronizationContext) the .net context is used for all Task.Run calls
In general Task.Run will also be run on a background thread by unity - however the problem lies when you want to execute something on the main-thread.

I am using TaskFactory to Run a Task on the unity main thread (the _mts variable contains the main thread scheduler). However the Unity default scheduler will only execute one task per frame, which can take a very long time if many tasks are run in the background that synchronize to the main thread. With the .Net Default Scheduler this works way better (because it handles multiple synchronizations per frame)

In the meantime I can recommend to use UniTask instead: https://github.com/Cysharp/UniTask - as it solves a lot of the problems (including handling exceptions from background tasks). It also handles switching to main thread much more efficiently.

Also in future versions Unity will support async/await natively which I’m quite excited about, see:
https://discussions.unity.com/t/836646 page-16#post-8024567