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Fixed in Unity 2018.2

Votes

0

Found in

Issue ID

1004428

Regression

No

Task.Delay(0) Hangs with Async Await

Scripting

-

-

Priority: 3Not yet prioritized for a release

-

Severity: 3Secondary functionality broken

Reported hangs with Async/Await

https://forum.unity.com/threads/task-yield-task-delay-0-hang.518045/

using System.Threading.Tasks;

using UnityEngine;

public class Test : MonoBehaviour
{
void Start()
{
TestAsync();
}

async void TestAsync()
{
int i = 0;
while (true)
{
Debug.Log($"### TestAsync: {++i}");
await Task.Delay(1); // ok
// await Task.Delay(0); // hang!
// await Task.Yield(); // hang!
}
}
}

Update:
I've looked at this issue and found that Task.Delay(0) runs synchronously. You can find details about this behavior on stackoverflow https://stackoverflow.com/questions/36939006/not-using-await-task-delayx-x0-makes-ui-thread-freeze

We have made one change due to this report however. Currently, when processing async/await continuations, we currently process the continuations that are spawned from existing continuations. This is why Task.Yield() would hang. Instead soon (once the changes land in 2018.1), if an "awaited" function calls await again, that continuation will be processed on to the next pass through the player loop. I should mention that we're also considering changes to where we process continuations in the playerloop (currently fixedupdate) since this behavior seems inconsistent in some ways with how other .NET implementations work.

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