unity-unitask-design

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Source-anchored design rules for Cysharp UniTask 2.5.10 (Unity 2018.4+) — struct semantics, PlayerLoop timing, cancellation, composition, conversion, async enumerables, triggers, and pitfalls. Use when writing or reviewing async UniTask code, choosing PlayerLoopTiming, handling CancellationToken, or composing WhenAll/WhenAny, even if the user just says "异步" or "零分配async". 为 Cysharp UniTask 2.5.10(Unity 2018.4+)提供源码锚定的设计规则(struct 语义、PlayerLoop 时机、取消、组合、转换、异步流、触发器、陷阱);当用户要编写或审查 async UniTask 代码、选择 PlayerLoopTiming、处理 CancellationToken、或组合 WhenAll/WhenAny 时使用。

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UniTask - Design Rules

Advisory module. Every rule is distilled from Cysharp UniTask source at:

2.5.10 — com.cysharp.unitask@2.5.10 (Unity 2018.4 baseline; actively used with 2022.3 / Unity 6)

Each rule cites a concrete file/line so the reasoning is auditable and the AI does not improvise against stale memory.

Mode: Documentation only — no REST skills to gate; load freely under any operating mode (Approval / Auto / Bypass).

When to Load This Module

Load before writing or reviewing any of:

Any async UniTask / async UniTask<T> / async UniTaskVoid method signature
.Forget(), .AttachExternalCancellation(token), .SuppressCancellationThrow() chaining
UniTask.Yield, UniTask.NextFrame, UniTask.Delay, UniTask.WaitForEndOfFrame, UniTask.WaitForFixedUpdate
UniTask.WaitUntil, UniTask.WaitWhile, UniTask.WaitUntilValueChanged, UniTask.WaitUntilCanceled
UniTask.WhenAll, UniTask.WhenAny, UniTask.WhenEach
UniTask.SwitchToMainThread, UniTask.SwitchToThreadPool, UniTask.Run
AsyncOperation.ToUniTask(), UnityWebRequest.SendWebRequest().ToUniTask(), Coroutine.ToUniTask()
this.GetCancellationTokenOnDestroy(), GetAsyncStartTrigger() and other AsyncTrigger* extensions
UniTaskCompletionSource / UniTaskCompletionSource<T> manual completion sources
IUniTaskAsyncEnumerable<T> / UniTaskAsyncEnumerable / AsyncReactiveProperty<T> / Channel<T>
WebGL-specific async code paths where Task.Run / SwitchToThreadPool are forbidden

Critical Rule Summary

#	Rule	Source anchor
1	`UniTask` is a `readonly partial struct` (value type). Once awaited, its `IUniTaskSource` is recycled; awaiting the same `UniTask` variable twice throws. Use `.Preserve()` to obtain a memoized copy that can be awaited multiple times.	`UniTask.cs:34`, `UniTask.cs:103-113`
2	A `UniTask` returned by a method must be either `await`ed, `.Forget()`ed, or `.AttachExternalCancellation(token)`ed. Orphan UniTasks silently swallow exceptions into `UniTaskScheduler.UnobservedTaskException`.	`UniTaskScheduler.cs:13`, `UniTaskVoid.cs:11-17`
3	`PlayerLoopTiming` defines 16 timing slots (2020.2+; 14 on older Unity). Default `UniTask.Yield()` / `UniTask.Delay` uses `PlayerLoopTiming.Update`. Mixing `LastPostLateUpdate` with legacy `WaitForEndOfFrame` coroutines changes observed frame ordering.	`PlayerLoopHelper.cs:71-99`
4	`UniTask.Delay(int ms, DelayType, PlayerLoopTiming, CancellationToken, bool cancelImmediately)` accepts `DelayType.DeltaTime / UnscaledDeltaTime / Realtime`. The old `bool ignoreTimeScale` overload still exists but mixes semantics — prefer the `DelayType` overload for new code.	`UniTask.Delay.cs:12-20`, `UniTask.Delay.cs:147-165`
5	`this.GetCancellationTokenOnDestroy()` is defined for `MonoBehaviour`, `GameObject`, and `Component` in `AsyncTriggerExtensions`. Plain C# classes do NOT receive this extension — they must own a `CancellationTokenSource` explicitly.	`Triggers/AsyncTriggerExtensions.cs:14,22,28`
6	`UniTask.WhenAll(params UniTask[] tasks)` and the `IEnumerable<UniTask>` overload both exist. Semantically match `Task.WhenAll` but are zero-alloc when tasks are UniTask-native. `WhenAny` returns `(winnerIndex, result)` tuple for `UniTask<T>`.	`UniTask.WhenAll.cs:12,22,31,41`, `UniTask.WhenAny.cs`
7	`AsyncOperation.ToUniTask(IProgress<float>, PlayerLoopTiming, CancellationToken)` is the canonical adapter. `await operation` works too but silently leaks the progress callback if you also set `operation.completed += …`.	`UnityAsyncExtensions.cs`
8	`UniTaskCompletionSource` and `UniTaskCompletionSource<T>` support `TrySetResult` / `TrySetException` / `TrySetCanceled`. Once any of the three succeeds, subsequent calls return `false` — they do not throw.	`UniTaskCompletionSource.cs:573,610,754,792`
9	`UniTask.SwitchToThreadPool()` and `UniTask.Run(...)` are compile-time available on all platforms BUT throw `NotSupportedException` at runtime on WebGL. Guard with `#if !UNITY_WEBGL
10	Returning `async UniTaskVoid` is the fire-and-forget idiom that lets `await` be used INSIDE the method. `async void` methods cannot return `UniTask` — a common compile error when porting from `Task`.	`UniTaskVoid.cs:11-17`, `UniTask.Factory.cs:112-131`

Sub-doc Routing

Sub-doc	When to read
BASICS.md	`UniTask` vs `Task` differences, struct semantics, `UniTaskVoid`, zero-alloc state machine, `AsyncUniTaskMethodBuilder`
PLAYERLOOP.md	16-value `PlayerLoopTiming` table, Yield/NextFrame/Delay/WaitForEndOfFrame/WaitForFixedUpdate, `DelayType`, frame-ordering with legacy coroutines
CANCELLATION.md	`CancellationToken` patterns, `GetCancellationTokenOnDestroy` (3 overloads), `AttachExternalCancellation`, `CancelAfterSlim`, `AddTo`, `OperationCanceledException` flow
COMPOSITION.md	`WhenAll`, `WhenAny`, `WhenEach`, `Forget`, `SuppressCancellationThrow`, `ContinueWith`, timeout patterns
CONVERSION.md	`AsyncOperation.ToUniTask`, `UnityWebRequest.SendWebRequest().ToUniTask`, `IEnumerator.ToUniTask`, `Task.AsUniTask`, `UniTask.AsTask`, `UniTask.ToCoroutine`
ASYNCENUMERABLE.md	`IUniTaskAsyncEnumerable<T>`, `UniTaskAsyncEnumerable`, `AsyncReactiveProperty<T>`, `Channel<T>`, `EveryValueChanged`, `Publish`, LINQ-to-async operators
TRIGGERS.md	`AsyncTriggerBase`, `GetAsyncStartTrigger`, `GetAsyncDestroyTrigger`, `OnCollisionEnterAsync`, `OnClickAsync`, `MonoBehaviourMessagesTriggers`, lifecycle cancellation
PITFALLS.md	30 concrete hallucination / runtime pitfalls (double-await, forgotten Forget, WebGL threadpool, tracker memory, wrong PlayerLoopTiming, coroutine interop bugs)

Routing to Other Modules

Choice between UniTask, raw Task, and IEnumerator at the architecture layer → load async
DOTween tween → UniTask adapter (tween.ToUniTask(TweenCancelBehaviour, token)) → load dotween-design
YooAsset handle → UniTask via handle.ToUniTask() extension → load yooasset-design
Addressables AsyncOperationHandle.ToUniTask() rules → load addressables-design
Performance review of UniTask-heavy code paths (tracker cost, state machine alloc) → load performance
Asmdef layout for UniTask consumers (Cysharp.Threading.Tasks.asmdef reference) → load asmdef

Version Scope

Targets UniTask 2.5.10. Earlier 2.x versions are mostly source-compatible; key differences:

WaitForEndOfFrame(MonoBehaviour coroutineRunner) overload added in recent 2.x — on 2023.1+ a parameterless overload is available (#if UNITY_2023_1_OR_NEWER). See UniTask.Delay.cs:78-103.
UniTask.WhenEach is a newer addition; not all 2.x builds ship it.

When in doubt, read the cited source — not your memory.