Async/await and webgl builds

@stonstad I have some news for you.
I dont know how, but I have successfully built the threads enabled project.

What does the program do:

• Starts unity job to cut a mesh with a plane in two parts.
• Awaits the cut result
• Takes the edge of cut and tesselates it to cap holes with UniTask.Run(()=>TesselationCodeHere())
• Awaits the tesselation result
• Writes meshdata (using unity 2020.1 new MeshData API https://docs.google.com/document/d/1QC7NV7JQcvibeelORJvsaTReTyszllOlxdfEsaVL2oA/edit#)

The results:
Sometimes program freezes, it looks like race condition or something similar. I have 100% CPU usage and program freeze. No Cut result in this situation:


Sometimes I get outofmemory errors, like in one of your posts:
Some of the errors in console and alert log: (they can have little difference from time to time)


And rarely the result is successfull:


Built in Unity 2020.1.0f1
The build tested in Chrome version 84.0.4147.125, 64 bit
Desktop builds work successfull in same situations. But I think I should try more simple tests for this api, cause I have no idea how to debug this

 

I am very sorry for spamming the forum. I've got one more interesting error.

 

Your earlier post helped me to get my code stable! Thank you! Although I had replaced all instances of System.Threading.Task.Run earlier, I still had a few UniTask.Run statements that I didn't realize were operating on the Unity threadpool. When I changed this code to coroutines random memory access / buffer errors stopped appearing.

When the unintentional threading was enabled I also saw strange (and random) casting errors similar to what you describe above.

Here is a summary of the issues I encountered with WebGL threading enabled:

• async/await works -- but you must be absolutely certain that no threading exists otherwise random failures will occur.
• any class which depends on system.threading will likely fail randomly. This includes concurrent collections, such as ConcurrentDictionary and ConcurrentQueue.
• Using generics and inheritance can cause runtime AOT compilation issues that won't be accurately reported unless you are including debugging symbols.
• External libraries which expose async/await interfaces likely use threading and won't work reliably. In my case I had to replace HttpClient (.NET library, built-in) with the Best HTTP plugin and replace all instances of System.Threading.Task with UniTask.

 

@DrViJ Are you able to use System.Linq without error when threading is enabled?

 

@stonstad Yes, I did not notice any problems with Linq usage. Maybe you can show an example to try to reproduce.

 

these are great news! thank you for your work!

 

@brendanduncan_u3d Much appreciate the update. We have a WebGL application that is ready for production release. Our only blocker at this time is WebGL stability -- we get many of the random errors described above.

 

@brendanduncan_u3d thank you for this information!

 

@brendanduncan_u3d @JoshPeterson I'm getting conflicting information on the support side. They are saying multithreading via C# will be unsupported: https://forum.unity.com/threads/multithreading-and-webgl.817986/#post-6337476 I hope this is incorrect. I'm merely advocating for Unity developers when I say multithreading is critically important, especially for third-party library compatibility.

 

@DrViJ I'm not any closer to finding stability. I converted UniTask coroutines to vanilla Unity coroutines with enumerators which are then awaited using GetAwaiter(). I don't get errors with stack traces as often as I get freezes. The WebGL player just freezes and the tab or whole browser must be closed.

 

@JoshPeterson
I have small question.
Does Unity team have any plan to improve async/await support in webgl with single thread?
For example make System.Threading.ThreadPool with just one thread (like in mono-wasm and Blazor) and/or reimplement System.Threading.Timer.

 

Hello.

Can you tell me any news on the progress of the fix? Is the issue in 2019.4.x not resolved?

 

@JoshPeterson and @brendanduncan_u3d I am also interested in understanding progress.

 

Async/Await works for me in 2019.4, but can't use Task.Delay (as mentioned in this thread). I replaced it with the code below.

Code (CSharp):

1.     public static async Task DelayAsync(float secondsDelay)
2.     {
3.         float startTime = Time.time;
4.         while (Time.time < startTime + secondsDelay) await Task.Yield();
5.     }

The remaining functionality such as Task.Yield seems to work.

 

A small package that makes it possible to use more Task functionality without worrying that something will be scheduled to other threads.
This package patch some BCL types to make it possible:
- ThreadPool implementation is changed to use only one available thread.
- Timer implementation is changed to use js timers. This makes Task.Delay safe to use

https://github.com/VolodymyrBS/WebGLThreadingPatcher.git

 

@VolodymyrBS Is this case supposed to work with your plugin?

Code (CSharp):

1. public class App : MonoBehaviour
2. {
3.     void Start()
4.     {
5.         AwaitTask();
6.     }
7.  
8.     private async void AwaitTask()
9.     {
10.         Debug.Log($"AwaitTask started");
11.         await Task.Run(() => {
12.             Debug.Log($"inside Task.Run");
13.         });
14.         Debug.Log($"After await Task.Run");
15.     }
16. }

I only see the first log

 

Yes, this should work.
What Unity version did you use?

 

@VolodymyrBS For this test I was on 2020.2.1f1, but my larger project that I want to integrate this in, is on 2020.1.14f1

 

brendanduncan_u3d any we will get special BCL implementation in WebGL?
For instance, I mean:
- ThreadPool with one thread;
- Timer based on js engine capabilities and not on the additional thread;
- HttpMessageHandler rewrote to work based on js engine capabilities.

A similar approach already used in Blazor WASM. With such BCL we could use almost any .NET assembly without worry.
IMO there good chance to do so while updating Unity BCL to .NET Standard 2.1 / .NET 6

 

Hey, I'd really like this plugin (wrote you on GitHub). Can you take a look into updating it to work with unity 2021?

 

I can confirm @VolodymyrBS made it work and I'm currently using async/await with UniTask flawlessly, Unity 2021.3.6 The library actually is quite advanced and lots of work was put into it. I highly recommend it!

 

could you please elaborate how you made this change practically ? I just replaced Task.Delay(5000) by Task.Yeld(5000) but does not seem to work...

 

Had the same problem and the fix was using this: https://github.com/Cysharp/UniTask

 

Thanks for this one.