UniTask provides lightweight alternatives to Tasks and async/await in Unity that have zero allocation overhead and integrate well with coroutines and the Unity runtime. Key features include UniTask/UniTask<T> that replace Task/Task<T>, methods like Delay and Yield that replace coroutines, and support for timeouts, cancellation, progress reporting, and multithreading. It also implements IAsyncEnumerable for async LINQ queries and reactive extensions for binding asynchronous data to Unity components.

1. UniTask
async/await Task in Unity
Introduction
River, 2022/5/29

2. Why
• Unity 官方不推薦使用 async/await 寫法
• UniTask (用過的都說讚)
• Optimization: for zero GC allocation
• Integrate Coroutine & Unity PlayerLoopTiming
• MonoBehaviour lifecycle cancellation

3. UniTask<T> / UniTask
• Lightweight alternative of Task<T>, zero allocation and fast excution
for zero overhead async/await integrate with Unity
• .WithCancellation enables Cancel, GetCancellationTokenOnDestroy
synchornizes with lifetime of GameObject
• .ToUniTask accepts progress callback(and all options), Progress.Create
is a lightweight alternative of IProgress<T>
var asset2 = await Resources.LoadAsync<TextAsset>("bar")
.WithCancellation(this.GetCancellationTokenOnDestroy());
var asset3 = await Resources.LoadAsync<TextAsset>("baz")
.ToUniTask(Progress.Create<float>(x => Debug.Log(x)));

4. • Delay
• Yield
• WaitFor series
await UniTask.DelayFrame(100);
// replacement of yield return new WaitForSeconds/WaitForSecondsRealtime
await UniTask.Delay(TimeSpan.FromSeconds(10), ignoreTimeScale: false);
// (PreUpdate, Update, LateUpdate, etc...)
await UniTask.Yield(PlayerLoopTiming.PreLateUpdate);
// replacement of yield return null
await UniTask.Yield();
await UniTask.NextFrame();
await UniTask.WaitForEndOfFrame(this); // this is MonoBehaviour
await UniTask.WaitForFixedUpdate();
await UniTask.WaitUntil(() => isActive == false);
await UniTask.WaitUntilValueChanged(this, x => x.isActive);

5. • Coroutine & Task
• Switch Thread
• WhenAll
// You can await IEnumerator coroutines
await FooCoroutineEnumerator();
// You can await a standard task
await Task.Run(() => 100);
// Multithreading, run on ThreadPool under this code
await UniTask.SwitchToThreadPool();
/* work on ThreadPool */
// return to MainThread
await UniTask.SwitchToMainThread();
/* work on main thread */
// concurrent async-wait and get results easily by tuple syntax
var (google, bing, yahoo) = await UniTask.WhenAll(task1, task2, task3);
// shorthand of WhenAll, tuple can await directly
var (google2, bing2, yahoo2) = await (task1, task2, task3);

6. • Timeout
• TimeoutController (optimized)
var cts = new CancellationTokenSource();
cts.CancelAfterSlim(TimeSpan.FromSeconds(5)); // 5sec timeout.
try
{
await UnityWebRequest.Get("http://foo").SendWebRequest().WithCancellation(cts.Token);
}
catch (OperationCanceledException ex)
{
if (ex.CancellationToken == cts.Token) { ... } // 5sec timeout
}
TimeoutController timeoutController = new TimeoutController(); // setup to field for reuse.
async UniTask FooAsync()
{
try
{
// you can pass timeoutController.Timeout(TimeSpan) to cancellationToken.
await UnityWebRequest.Get("http://foo").SendWebRequest()
.WithCancellation(timeoutController.Timeout(TimeSpan.FromSeconds(5)));
timeoutController.Reset(); // call Reset(Stop timeout timer and ready for reuse) when succeed.
}
catch (OperationCanceledException ex)
{
if (timeoutController.IsTimeout()) { ... } // timeout
}
}

7. • Progress (.Create(), IProgress<>)
• Better than System.Progress
var progress = Progress.Create<float>(x => Debug.Log(x));
var request = await UnityWebRequest.Get("http://google.co.jp").SendWebRequest()
.ToUniTask(progress: progress);
public class Foo : MonoBehaviour, IProgress<float>
{
public void Report(float value)
{
UnityEngine.Debug.Log(value);
}
public async UniTaskVoid WebRequest()
{
var request = await UnityWebRequest.Get("http://google.co.jp").SendWebRequest()
.ToUniTask(progress: this); // pass this
}
}

8. • PlayerLoop - UniTask run on a custom PlayerLoop
• PlayerLoopTiming
• Initialization = 0,
• LastInitialization = 1,
• EarlyUpdate = 2,
• LastEarlyUpdate = 3,
• FixedUpdate = 4,
• LastFixedUpdate = 5,
• PreUpdate = 6,
• LastPreUpdate = 7,
• Update = 8,
• LastUpdate = 9,
• PreLateUpdate = 10,
• LastPreLateUpdate = 11,
• PostLateUpdate = 12,
• LastPostLateUpdate = 13
• TimeUpdate = 14,
• LastTimeUpdate = 15,

9. async void vs async UniTaskVoid
• async void – not run on UniTask systems. 不建議使用
• async UniTaskVoid 建議使用
• Lightweight of async UniTask
• No awaitable completion (fire and forgot)
• Report error/exception immediately to UniTaskSchedular.UnobservedTaskException
• Async lambda (for event) 建議使用 UniTask.Action / UniTask.UnityAction
// Bad: async void
actEvent += async () => { }; unityEvent += async () => { };
// Ok: create Action delegate by lambda
actEvent += UniTask.Action(async () => { await UniTask.Yield(); });
unityEvent += UniTask.UnityAction(async () => { await UniTask.Yield(); });
async UniTaskVoid Start() { ... }

10. 第三方/插件整合
• TextMeshPro
• Addressables
• DOTween

11. AsyncEnumerable and Async LINQ
• UniTaskAsyncEnumerable implements asynchronous LINQ, similar to
LINQ in IEnumerable<T> or Rx in IObservable<T>. All standard LINQ
query operators can be applied to asynchronous streams.

12. Awaitable Events
• All UGUI implements ***AsAsyncEnumerable
• All MonoBehaviour message events can convert async-streams

13. • AsyncReactiveProperty, AsyncReadOnlyReactiveProperty
• ReactiveProperty.
• BindTo extension method: binding asynchronous stream values to Unity
components(Text/Selectable/TMP/Text).
var rp = new AsyncReactiveProperty<int>(99);
// AsyncReactiveProperty itself is IUniTaskAsyncEnumerable, you can query by LINQ
rp.ForEachAsync(x => { Debug.Log(x); },
this.GetCancellationTokenOnDestroy())
.Forget();
rp.Value = 10; // push 10 to all subscriber
rp.Value = 11; // push 11 to all subscriber
// WithoutCurrent ignore initial value; BindTo bind stream value to unity components.
rp.WithoutCurrent().BindTo(this.textComponent);
await rp.WaitAsync(); // wait until next value set

14. Channel
• 取代 System.Threading.Tasks.Channels，類似 GoLang Channel
• Currently it only supports multiple-producer, single-consumer
unbounded channels.
• For producer(.Writer), use TryWrite to push value and TryComplete to
complete channel.
• For consumer(.Reader), use TryRead, WaitToReadAsync, ReadAsync,
Completion and ReadAllAsync to read queued messages