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Fixed in 2018.2

Fixed in 2018.1



Found in

Issue ID




Task.Delay(0) Hangs with Async Await



Reported hangs with Async/Await

using System.Threading.Tasks;

using UnityEngine;

public class Test : MonoBehaviour
void Start()

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!

I've looked at this issue and found that Task.Delay(0) runs synchronously. You can find details about this behavior on stackoverflow

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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