Advanced tips, see blog post: [Extends UnityWebRequest via async decorator pattern — Advanced Techniques of UniTask](https://medium.com/@neuecc/extends-unitywebrequest-via-async-decorator-pattern-advanced-techniques-of-unitask-ceff9c5ee846)
Install via [UPM package](#upm-package) or asset package(`UniTask.*.*.*.unitypackage`) available in [UniTask/releases](https://github.com/Cysharp/UniTask/releases) page.
UniTask feature rely on C# 7.0([task-like custom async method builder feature](https://github.com/dotnet/roslyn/blob/master/docs/features/task-types.md)) so required Unity version is after `Unity 2018.3`, officialy lower support version is `Unity 2018.4.13f1`.
Why UniTask(custom task-like object) is required? Because Task is too heavy, not matched to Unity threading(single-thread). UniTask does not use thread and SynchronizationContext/ExecutionContext because almost Unity's asynchronous object is automaticaly dispatched by Unity's engine layer. It acquires more fast and more less allocation, completely integrated with Unity.
You can await `AsyncOperation`, `ResourceRequest`, `AssetBundleRequest`, `AssetBundleCreateRequest`, `UnityWebRequestAsyncOperation`, `AsyncGPUReadbackRequest`, `IEnumerator` and others when `using Cysharp.Threading.Tasks;`.
`WithCancellation` is a simple version of `ToUniTask`, both returns `UniTask`. Details of cancellation, see: [Cancellation and Exception handling](#cancellation-and-exception-handling) section.
> Note: WithCancellation is returned from native timing of PlayerLoop but ToUniTask is returned from specified PlayerLoopTiming. Details of timing, see: [PlayerLoop](#playerloop) section.
> Note: AssetBundleRequest has `asset` and `allAssets`, in default await returns `asset`. If you want to get `allAssets`, you can use `AwaitForAllAssets()` method.
The type of `UniTask` can use utility like `UniTask.WhenAll`, `UniTask.WhenAny`. It is like Task.WhenAll/WhenAny but return type is more useful, returns value tuple so can deconsrtuct each result and pass multiple type.
If you want to convert async to coroutine, you can use `.ToCoroutine()`, this is useful to use only allow coroutine system.
UniTask can not await twice. This is a similar constraint to the [ValueTask/IValueTaskSource](https://docs.microsoft.com/en-us/dotnet/api/system.threading.tasks.valuetask-1?view=netcore-3.1) introduced in .NET Standard 2.1.
> The following operations should never be performed on a ValueTask<TResult> 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.
Store to the class field, you can use `UniTask.Lazy` that gurantee call multipletimes. `.Preserve()` allows for multiple calls (internally cached results). This is useful when multiple calls in a function scope.
Some UniTask factory methods have `CancellationToken cancellationToken = default` parameter. Andalso some async operation for unity have `WithCancellation(CancellationToken)` and `ToUniTask(..., CancellationToken cancellation = default)` extension methods.
You can pass `CancellationToken` to parameter by standard [`CancellationTokenSource`](https://docs.microsoft.com/en-us/dotnet/api/system.threading.cancellationtokensource).
When detect cancellation, all methods throws `OperationCanceledException` and propagate to upstream. `OperationCanceledException` is special exception, if not handled this exception, finally it is propagated to `UniTaskScheduler.UnobservedTaskException`.
Default behaviour of received unhandled exception is write log as exception. Log level can change by `UniTaskScheduler.UnobservedExceptionWriteLogType`. If you want to change custom beavhiour, set action to `UniTaskScheduler.UnobservedTaskException.`
If you want to cancel behaviour in async UniTask method, throws `OperationCanceledException` manually.
```csharp
public async UniTask<int> FooAsync()
{
await UniTask.Yield();
throw new OperationCanceledException();
}
```
If you handle exception but want to ignore(propagete to global cancellation handling), use exception filter.
```csharp
public async UniTask<int> BarAsync()
{
try
{
var x = await FooAsync();
return x * 2;
}
catch (Exception ex) when (!(ex is OperationCanceledException))
{
return -1;
}
}
```
throws/catch `OperationCanceledException` is slightly heavy, if you want to care performance, use `UniTask.SuppressCancellationThrow` to avoid OperationCanceledException throw. It returns `(bool IsCanceled, T Result)` instead of throw.
```csharp
var (isCanceled, _) = await UniTask.DelayFrame(10, cancellationToken: cts.Token).SuppressCancellationThrow();
Note: Only suppress throws if you call it directly into the most source method. Otherwise, the return value will be converted, but the entire pipeline will not be suppressed throws.
You should not use standard `new System.Progress<T>`, because it causes allocation every times. Use `Cysharp.Threading.Tasks.Progress` instead. This progress factory has two methods, `Create` and `CreateOnlyValueChanged`. `CreateOnlyValueChanged` calls only when progress value changed.
UniTask is run on custom [PlayerLoop](https://docs.unity3d.com/ScriptReference/LowLevel.PlayerLoop.html). UniTask's playerloop based method(such as `Delay`, `DelayFrame`, `asyncOperation.ToUniTask`, etc...) accepts this `PlayerLoopTiming`.
```csharp
public enum 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
}
```
It indicates when to run, you can check [PlayerLoopList.md](https://gist.github.com/neuecc/bc3a1cfd4d74501ad057e49efcd7bdae) to Unity's default playerloop and injected UniTask's custom loop.
`PlayerLoopTiming.Update` is similar as `yield return null` in coroutine, but it is called before Update(Update and uGUI events(button.onClick, etc...) are called on `ScriptRunBehaviourUpdate`, yield return null is called on `ScriptRunDelayedDynamicFrameRate`). `PlayerLoopTiming.FixedUpdate` is similar as `WaitForFixedUpdate`, `PlayerLoopTiming.LastPostLateUpdate` is similar as `WaitForEndOfFrame` in coroutine.
> `await UniTask.WaitForEndOfFrame()` is not equilavelnt to coroutine's `yield return new WaitForEndOfFrame()`. Coroutine's WaitForEndOfFrame seems to run after the PlayerLoop is done. Some methods that require coroutine's end of frame(`ScreenCapture.CaptureScreenshotAsTexture`, `CommandBuffer`, etc) does not work correctly when replace to async/await. In that case, use a coroutine.
`yield return null` and `UniTask.Yield` is similar but different. `yield return null` always return next frame but `UniTask.Yield` return next called, that is, call `UniTask.Yield(PlayerLoopTiming.Update)` on `PreUpdate`, it returns same frame. `UniTask.NextFrame()` gurantees return next frame, this would be expected to behave exactly the same as `yield return null`.
AsyncOperation is returned from native timing. For example, await `SceneManager.LoadSceneAsync` is returned from `EarlyUpdate.UpdatePreloading` and after called, loaded scene's `Start` called from `EarlyUpdate.ScriptRunDelayedStartupFrame`. Also `await UnityWebRequest` is returned from `EarlyUpdate.ExecuteMainThreadJobs`.
In UniTask, await directly and `WithCancellation` use native timing, `ToUniTask` use specified timing. This is usually not a particular problem, but with `LoadSceneAsync`, causes different order of Start and continuation after await. so recommend not to use `LoadSceneAsync.ToUniTask`.
In default, UniTask's PlayerLoop is initialized at `[RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]`.
The order in which methods are called in BeforeSceneLoad is indeterminate, so if you want to use UniTask in other BeforeSceneLoad methods, you should try to initialize it before this.
```csharp
// AfterAssembliesLoaded is called before BeforeSceneLoad
If you import Unity's `Entities` package, that reset custom player loop to default at `BeforeSceneLoad` and inject ECS's loop. When Unity call ECS's inject method after UniTask's initialize method, UniTask will no longer work.
To solve this issue, you can re-initialize UniTask PlayerLoop after ECS initialized.
```csharp
// Get ECS Loop.
var playerLoop = ScriptBehaviourUpdateOrder.CurrentPlayerLoop;
You can diagnostic UniTask's player loop is ready by `PlayerLoopHelper.IsInjectedUniTaskPlayerLoop()`. And also `PlayerLoopHelper.DumpCurrentPlayerLoop` shows current all playerloop to console.
`async void` is a standard C# task system so does not run on UniTask systems. It is better not to use. `async UniTaskVoid` is a lightweight version of `async UniTask` because it does not have awaitable completion and report error immediately to `UniTaskScheduler.UnobservedTaskException`. If you don't require to await it(fire and forget), use `UniTaskVoid` is better. Unfortunately to dismiss warning, require to using with `Forget()`.
Also UniTask have `Forget` method, it is similar with UniTaskVoid and same effects with it. However still UniTaskVoid is more efficient if completely do not use await。
```csharp
public async UniTask DoAsync()
{
// do anything...
await UniTask.Yield();
}
public void Caller()
{
DoAsync().Forget();
}
```
Using async lambda in register event, it is used `async void`. To avoid it, you can use `UniTask.Action` or `UniTask.UnityAction` that creates delegate via `async UniTaskVoid` lambda.
```csharp
Action actEvent;
UnityAction unityEvent; // especially used in uGUI
* Enable StackTrace(Toggle) - Capture StackTrace when task is started. Performance impact: high.
For debug use, enable tracking and capture stacktrace is useful but it it decline performance. Recommended usage is enable both to find task leak, and when done, finally disable both.
In default, UniTask supports TextMeshPro(`BindTo(TMP_Text)` and `TMP_InputField` event extensions like standard uGUI `InputField`), DOTween(`Tween` as awaitable) and Addressables(`AsyncOperationHandle` and `AsyncOpereationHandle<T>` as awaitable).
There are defined in separated asmdef like `UniTask.TextMeshPro`, `UniTask.DOTween`, `UniTask.Addressables`.
TextMeshPro and Addressables support are automatically enabled when import there package from package manager. However DOTween support, require to `com.demigiant.dotween` import from [OpenUPM](https://openupm.com/packages/com.demigiant.dotween/) or define `UNITASK_DOTWEEN_SUPPORT` to enable it.
DOTween support's default behaviour(`await`, `WithCancellation`, `ToUniTask`) awaits tween is killed. It works both Complete(true/false) and Kill(true/false). But if you want to tween reuse(`SetAutoKill(false)`), it does not work you expected. Or, if you want to await for another timing, the following extension methods exist in Tween, `AwaitForComplete`, `AwaitForPause`, `AwaitForPlay`, `AwaitForRewind`, `AwaitForStepComplete`.
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. For example, the following code shows how to apply a Where filter to a button-click asynchronous stream that runs once every two clicks.
```csharp
await okButton.OnClickAsAsyncEnumerable().Where((x, i) => i % 2 == 0).ForEachAsync(_ =>
Async LINQ is enabled when `using Cysharp.Threading.Tasks.Linq;`, and `UniTaskAsyncEnumerable` is defined in `UniTask.Linq` asmdef.
It's closer to UniRx (Reactive Extensions), but UniTaskAsyncEnumerable is a pull-based asynchronous stream, whereas Rx was a push-based asynchronous stream. Note that although similar, the characteristics are different and the details behave differently along with them.
`UniTaskAsyncEnumerable` is the entry point like `Enumerbale`. In addition to the standard query operators, there are other generators for Unity such as `EveryUpdate`, `Timer`, `TimerFrame`, `Interval`, `IntervalFrame`, and `EveryValueChanged`. And also added additional UniTask original query operators like `Append`, `Prepend`, `DistinctUntilChanged`, `ToHashSet`, `Buffer`, `CombineLatest`, `Do`, `Never`, `ForEachAsync`, `Pairwise`, `Publish`, `Queue`, `Return`, `SkipUntil`, `TakeUntil`, `SkipUntilCanceled`, `TakeUntilCanceled`, `TakeLast`, `Subscribe`.
How to create async iterator, C# 8.0 supports async iterator(`async yield return`) but it only allows `IAsyncEnumerable<T>` and of course requires C# 8.0. UniTask supports `UniTaskAsyncEnumerable.Create` method to create custom async iterator.
```csharp
// IAsyncEnumerable, C# 8.0 version of async iterator. ( do not use this style, IAsyncEnumerable is not controled in UniTask).
`AsyncReactiveProperty`, `AsyncReadOnlyReactiveProperty` is UniTask version of UniTask's ReactiveProperty. `BindTo` extension method of `IUniTaskAsyncEnumerable<T>` for binding asynchronous stream values to Unity components(Text/Selectable/TMP/Text).
A pull-type asynchronous stream does not get the next values until the asynchronous processing in the sequence is complete. This could spill data from push-type events such as buttons.
```csharp
// can not get click event during 3 seconds complete.
`Channel` is same as [System.Threading.Tasks.Channels](https://docs.microsoft.com/ja-jp/dotnet/api/system.threading.channels?view=netcore-3.1) that is similar as GoLang Channel.
Currently only supports multiple-producer, single-consumer unbounded channel. It can create by `Channel.CreateSingleConsumerUnbounded<T>()`.
For producer(`.Writer`), `TryWrite` to push value and `TryComplete` to complete channel. For consumer(`.Reader`), `TryRead`, `WaitToReadAsync`, `ReadAsync`, `Completion` and `ReadAllAsync` to read queued messages.
`ReadAllAsync` returns `IUniTaskAsyncEnumerable<T>` so query LINQ operators. Reader only allows single-consumer but use `.Publish()` query operator to enable multicast message. For example, make pub/sub utility.
Unity's `[UnityTest]` attribute can test coroutine(IEnumerator) but can not test async. `UniTask.ToCoroutine` bridges async/await to coroutine so you can test async method.
```csharp
[UnityTest]
public IEnumerator DelayIgnore() => UniTask.ToCoroutine(async () =>
UniTask itself's unit test is written by Unity Test Runner and [Cysharp/RuntimeUnitTestToolkit](https://github.com/Cysharp/RuntimeUnitTestToolkit) to check on CI and IL2CPP working.
Most UniTask methods run in a single thread (PlayerLoop), but only `UniTask.Run` and `UniTask.SwitchToThreadPool` run on a thread pool. If you use a thread pool, it won't work with WebGL and so on.
`UniTask.Run` will be deprecated in the future (marked with an Obsolete) and only `RunOnThreadPool` will be used. Also, if you use `UniTask.Run`, consider whether you can use `UniTask.Create` or `UniTask.Void`.
IEnumerator.ToUniTask limitation
---
You can convert coroutine(IEnumerator) to UniTask(or await directly) but has some limitations.
* Consuming loop timing is not same as StartCoroutine, it is used specified PlayerLoopTiming, and default's `PlayerLoopTiming.Update` is run before MonoBehaviour's Update and StartCoroutine's loop.
If you want to convert fully compatible from coroutine to async, use `IEnumerator.ToUniTask(MonoBehaviour coroutineRunner)` overload. It executes StartCoroutine on an instance of the argument MonoBehaviour and waits for it to complete in UniTask.
UniTask can run on Unity Edtitor like Editor Coroutine. However, there are some limitations.
* Delay, DelayFrame is not work correctly because can not get deltaTime in editor. Return the result of the await immediately; you can use `DelayType.Realtime` to wait for the right time.
* All PlayerLoopTiming run on timing, `EditorApplication.update`.
UniTask is aggressively caching async promise object to achive zero allocation(technical details, see blog post [UniTask v2 — Zero Allocation async/await for Unity, with Asynchronous LINQ](https://medium.com/@neuecc/unitask-v2-zero-allocation-async-await-for-unity-with-asynchronous-linq-1aa9c96aa7dd)). In default, cache all promises but you can configure `TaskPool.SetMaxPoolSize` to your value, the value indicates cache size per type. `TaskPool.GetCacheSizeInfo` returns current cached object in pool.
In UnityEditor profiler shows allocation of compiler generated AsyncStateMachine but it only occurs in debug(development) build. C# Compiler generate AsyncStateMachine as class on Debug build and as struct on Release build.
After Unity 2020.1 supports Code Optimization option on UnityEditor(right, footer).
You can change C# compiler optimization to release, it removes AsyncStateMachine allocation. Andalso optimization option can set via `Compilation.CompilationPipeline-codeOptimization`, and `Compilation.CodeOptimization`.
Unity's default SynchronizationContext(`UnitySynchronizationContext`) is poor implementation for performance. UniTask itself is bypass `SynchronizationContext`(and `ExecutionContext`) so does not use it but if exists in `async Task`, still used it. `UniTaskSynchronizationContext` is replacement of `UnitySynchronizationContext`, it is better for performance.
This is an optional choice and is not always recommended; `UniTaskSynchronizationContext` is less performance than `async UniTask` and is not a complete UniTask replacement. It also does not guarantee full behavioral compatibility with the `UnitySynchronizationContext`.
UniTask's API References is hosted at [cysharp.github.io/UniTask](https://cysharp.github.io/UniTask/api/Cysharp.Threading.Tasks.html) by [DocFX](https://dotnet.github.io/docfx/) and [Cysharp/DocfXTemplate](https://github.com/Cysharp/DocfxTemplate).
For example, UniTask's factory methods can see at [UniTask#methods](https://cysharp.github.io/UniTask/api/Cysharp.Threading.Tasks.UniTask.html#methods-1). UniTaskAsyncEnumerable's factory/extension methods can see at [UniTaskAsyncEnumerable#methods](https://cysharp.github.io/UniTask/api/Cysharp.Threading.Tasks.Linq.UniTaskAsyncEnumerable.html#methods-1).
After Unity 2019.3.4f1, Unity 2020.1a21, that support path query parameter of git package. You can add `https://github.com/Cysharp/UniTask.git?path=src/UniTask/Assets/Plugins/UniTask` to Package Manager
If you want to set a target version, UniTask is using `*.*.*` release tag so you can specify a version like `#2.0.36`. For example `https://github.com/Cysharp/UniTask.git?path=src/UniTask/Assets/Plugins/UniTask#2.0.36`.
The package is available on the [openupm registry](https://openupm.com). It's recommended to install it via [openupm-cli](https://github.com/openupm/openupm-cli).
UniTask of .NET Core version is a subset of Unity UniTask, removed PlayerLoop dependent methods.
It runs at higher performance than the standard Task/ValueTask, but you should be careful to ignore the ExecutionContext/SynchronizationContext when using it. `AysncLocal` also does not work because it ignores ExecutionContext.
If you use UniTask internally, but provide ValueTask as an external API, you can write like the following(Inspired by [PooledAwait](https://github.com/mgravell/PooledAwait)).
.NET Core version is intended to allow users to use UniTask as an interface when sharing code with Unity (such as [Cysharp/MagicOnion](https://github.com/Cysharp/MagicOnion/)). .NET Core version of UniTask enables smooth code sharing.
Utility methods such as WhenAll which is equivalent to UniTask are provided as [Cysharp/ValueTaskSupplement](https://github.com/Cysharp/ValueTaskSupplement).
