UniTask

Provides an efficient allocation free async/await integration for Unity.

• Struct based UniTask<T> and custom AsyncMethodBuilder to achieve zero allocation
• Makes all Unity AsyncOperations and Coroutines awaitable
• PlayerLoop based task(UniTask.Yield, UniTask.Delay, UniTask.DelayFrame, etc..) that enable replacing all coroutine operations
• MonoBehaviour Message Events and uGUI Events as awaitable/async-enumerable
• Runs completely on Unity's PlayerLoop so doesn't use threads and runs on WebGL, wasm, etc.
• Asynchronous LINQ, with Channel and AsyncReactiveProperty
• TaskTracker window to prevent memory leaks
• Highly compatible behaviour with Task/ValueTask/IValueTaskSource

For technical details, see blog post: UniTask v2 — Zero Allocation async/await for Unity, with Asynchronous LINQ
For advanced tips, see blog post: Extends UnityWebRequest via async decorator pattern — Advanced Techniques of UniTask

Table of Contents

• Getting started
• Basics of UniTask and AsyncOperation
• Cancellation and Exception handling
• Timeout handling
• Progress
• PlayerLoop
• async void vs async UniTaskVoid
• UniTaskTracker
• External Assets
• AsyncEnumerable and Async LINQ
• Awaitable Events
• Channel
• vs Awaitable
• For Unit Testing
• ThreadPool limitation
• IEnumerator.ToUniTask limitation
• For UnityEditor
• Compare with Standard Task API
• Pooling Configuration
• Allocation on Profiler
• UniTaskSynchronizationContext
• API References
• UPM Package
• Install via git URL
• .NET Core
• License

Getting started

Install via UPM package with git reference or asset package(UniTask.*.*.*.unitypackage) available in UniTask/releases.

// extension awaiter/methods can be used by this namespace
using Cysharp.Threading.Tasks;

// You can return type as struct UniTask<T>(or UniTask), it is unity specialized lightweight alternative of Task<T>
// zero allocation and fast excution for zero overhead async/await integrate with Unity
async UniTask<string> DemoAsync()
{
    // You can await Unity's AsyncObject
    var asset = await Resources.LoadAsync<TextAsset>("foo");
    var txt = (await UnityWebRequest.Get("https://...").SendWebRequest()).downloadHandler.text;
    await SceneManager.LoadSceneAsync("scene2");

    // .WithCancellation enables Cancel, GetCancellationTokenOnDestroy synchornizes with lifetime of GameObject
    // after Unity 2022.2, you can use `destroyCancellationToken` in MonoBehaviour
    var asset2 = await Resources.LoadAsync<TextAsset>("bar").WithCancellation(this.GetCancellationTokenOnDestroy());

    // .ToUniTask accepts progress callback(and all options), Progress.Create is a lightweight alternative of IProgress<T>
    var asset3 = await Resources.LoadAsync<TextAsset>("baz").ToUniTask(Progress.Create<float>(x => Debug.Log(x)));

    // await frame-based operation like a coroutine
    await UniTask.DelayFrame(100); 

    // replacement of yield return new WaitForSeconds/WaitForSecondsRealtime
    await UniTask.Delay(TimeSpan.FromSeconds(10), ignoreTimeScale: false);

    // yield any playerloop timing(PreUpdate, Update, LateUpdate, etc...)
    await UniTask.Yield(PlayerLoopTiming.PreLateUpdate);

    // replacement of yield return null
    await UniTask.Yield();
    await UniTask.NextFrame();

    // replacement of WaitForEndOfFrame
#if UNITY_2023_1_OR_NEWER
    await UniTask.WaitForEndOfFrame();
#else
    // requires MonoBehaviour(CoroutineRunner))
    await UniTask.WaitForEndOfFrame(this); // this is MonoBehaviour
#endif

    // replacement of yield return new WaitForFixedUpdate(same as UniTask.Yield(PlayerLoopTiming.FixedUpdate))
    await UniTask.WaitForFixedUpdate();

    // replacement of yield return WaitUntil
    await UniTask.WaitUntil(() => isActive == false);

    // special helper of WaitUntil
    await UniTask.WaitUntilValueChanged(this, x => x.isActive);

    // 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(same as `ObserveOnMainThread` in UniRx)
    await UniTask.SwitchToMainThread();

    // get async webrequest
    async UniTask<string> GetTextAsync(UnityWebRequest req)
    {
        var op = await req.SendWebRequest();
        return op.downloadHandler.text;
    }

    var task1 = GetTextAsync(UnityWebRequest.Get("http://google.com"));
    var task2 = GetTextAsync(UnityWebRequest.Get("http://bing.com"));
    var task3 = GetTextAsync(UnityWebRequest.Get("http://yahoo.com"));

    // 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);

    // return async-value.(or you can use `UniTask`(no result), `UniTaskVoid`(fire and forget)).
    return (asset as TextAsset)?.text ?? throw new InvalidOperationException("Asset not found");
}

Basics of UniTask and AsyncOperation

UniTask features rely on C# 7.0(task-like custom async method builder feature) so the required Unity version is after Unity 2018.3, the official lowest version supported is Unity 2018.4.13f1.

Why is UniTask(custom task-like object) required? Because Task is too heavy and not matched to Unity threading (single-thread). UniTask does not use threads and SynchronizationContext/ExecutionContext because Unity's asynchronous object is automaticaly dispatched by Unity's engine layer. It achieves faster and lower allocation, and is completely integrated with Unity.

You can await AsyncOperation, ResourceRequest, AssetBundleRequest, AssetBundleCreateRequest, UnityWebRequestAsyncOperation, AsyncGPUReadbackRequest, IEnumerator and others when using Cysharp.Threading.Tasks;.

UniTask provides three pattern of extension methods.

* await asyncOperation;
* .WithCancellation(CancellationToken);
* .ToUniTask(IProgress, PlayerLoopTiming, CancellationToken);

WithCancellation is a simple version of ToUniTask, both return UniTask. For details of cancellation, see: Cancellation and Exception handling section.

Note: await directly is returned from native timing of PlayerLoop but WithCancellation and ToUniTask are returned from specified PlayerLoopTiming. For details of timing, see: PlayerLoop section.

Note: AssetBundleRequest has asset and allAssets, default await returns asset. If you want to get allAssets, you can use AwaitForAllAssets() method.

The type of UniTask can use utilities like UniTask.WhenAll, UniTask.WhenAny, UniTask.WhenEach. They are like Task.WhenAll/Task.WhenAny but the return type is more useful. They return value tuples so you can deconstruct each result and pass multiple types.

public async UniTaskVoid LoadManyAsync()
{
    // parallel load.
    var (a, b, c) = await UniTask.WhenAll(
        LoadAsSprite("foo"),
        LoadAsSprite("bar"),
        LoadAsSprite("baz"));
}

async UniTask<Sprite> LoadAsSprite(string path)
{
    var resource = await Resources.LoadAsync<Sprite>(path);
    return (resource as Sprite);
}

If you want to convert a callback to UniTask, you can use UniTaskCompletionSource<T> which is a lightweight edition of TaskCompletionSource<T>.

public UniTask<int> WrapByUniTaskCompletionSource()
{
    var utcs = new UniTaskCompletionSource<int>();

    // when complete, call utcs.TrySetResult();
    // when failed, call utcs.TrySetException();
    // when cancel, call utcs.TrySetCanceled();

    return utcs.Task; //return UniTask<int>
}

You can convert Task -> UniTask: AsUniTask, UniTask -> UniTask<AsyncUnit>: AsAsyncUnitUniTask, UniTask<T> -> UniTask: AsUniTask. UniTask<T> -> UniTask's conversion cost is free.

If you want to convert async to coroutine, you can use .ToCoroutine(), this is useful if you want to only allow using the coroutine system.

UniTask can not await twice. This is a similar constraint to the ValueTask/IValueTaskSource introduced in .NET Standard 2.1.

The following operations should never be performed on a ValueTask instance:

• Awaiting the instance multiple times.
• Calling AsTask multiple times.
• Using .Result or .GetAwaiter().GetResult() when the operation hasn't yet completed, or using them multiple times.
• Using more than one of these techniques to consume the instance.

If you do any of the above, the results are undefined.

var task = UniTask.DelayFrame(10);
await task;
await task; // NG, throws Exception

Store to the class field, you can use UniTask.Lazy that supports calling multiple times. .Preserve() allows for multiple calls (internally cached results). This is useful when there are multiple calls in a function scope.

Also UniTaskCompletionSource can await multiple times and await from many callers.

Cancellation and Exception handling

Some UniTask factory met