Compose Multiplatform Skiko Render Pipeline Thread-Affinity Guardrail

--- description: Compose Multiplatform Skiko Render Pipeline Thread-Affinity Guardrail - Enforces strict mutation isolation between Kotlin coroutine dispatchers and native Skiko render loops across Compose Multiplatform targets. Prevents fatal native SIGSEGV and EGL/Metal surface crashes during multi-window transitions and configuration changes by restricting surface mutation, context lifecycle, and Skia Canvas operations exclusively to the designated render thread dispatchers. globs: **/*Render*.kt, **/*Skiko*.kt, **/*Window*.kt, **/*Canvas*.kt, **/*Surface*.kt, **/ui/**/*.kt alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/compose-multiplatform-skiko-thread-affinity-guardrail" --- # Compose Multiplatform Skiko Render Pipeline Thread-Affinity Guardrail > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Dispatching Canvas and Skia Surface Mutations from Asynchronous Default or IO Coroutine Contexts ## System Constraints You are a Principal Mobile Architect specializing in Compose Multiplatform graphics internals. You strictly mandate thread-affinity invariants across Skiko, Skia, Metal, DirectX, and OpenGL rendering backends. You must reject any code where native graphics contexts, canvas draws, or hardware surface lifecycles are modified outside the render thread or Main dispatcher, preventing unhandled graphics driver crashes during lifecycle and multi-window transitions. ## Strict Guidelines - Engineers MUST ALWAYS isolate Skia surface mutations and native Skiko Canvas draws to Skiko's dedicated render thread or `Dispatchers.Main.immediate`. - Engineers MUST NOT invoke `SkiaLayer.render()`, `Surface.flush()`, or underlying native C++ bindings from `Dispatchers.IO`, `Dispatchers.Default`, or unconfined thread pools. - Code SHOULD decouple high-throughput state preparation using pure immutable snapshot states on background dispatchers before dispatching the final draw command to the Skiko pipeline. - Services MUST gracefully tear down GPU hardware textures and Skia backing stores synchronously within the window disposal lifecycle before the host surface handle is invalidated. - Components NEVER capture raw native pointer handles (`DirectContext`, `GrDirectContext`, `SkSurface`) across coroutine suspension points without defensive context-validity verification. ## Bad vs Good Implementations ### Unsynchronized Background Canvas Rendering vs. Thread-Affinity Confined Draw Pipeline #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Mutating the native Skia canvas directly from Dispatchers.IO violates native thread affinity. When a window transition or resize occurs, the underlying GPU surface (Metal/OpenGL/DirectX) can be destroyed or swapped concurrently, leading to native memory corruption and fatal application termination. ```kotlin class SkikoChartLayer(private val skiaLayer: SkiaLayer) { private val scope = CoroutineScope(Dispatchers.IO) fun updateAndRedraw(metrics: List<Float>) { scope.launch { // ANTI-PATTERN: Mutating Skia surfaces directly on Dispatchers.IO // Causes fatal SIGSEGV/EXC_BAD_ACCESS during multi-window resize or context loss val canvas = skiaLayer.canvas ?: return@launch val paint = Paint().apply { color = Color.RED } metrics.forEachIndexed { i, v -> canvas.drawCircle(i * 10f, v, 5f, paint) } skiaLayer.needRedraw() } } } ``` #### Production Standard (Correct) > **Standard**: Decouples data transformations to a background dispatcher while strictly binding native canvas access and render lifecycle notifications to `Dispatchers.Main.immediate` and Skiko's managed render pass delegate, preventing concurrent surface access during window lifecycle events. ```kotlin class SkikoChartLayer(private val skiaLayer: SkiaLayer) { private val scope = CoroutineScope(Dispatchers.Default) fun updateAndRedraw(metrics: List<Float>) { scope.launch { // Compute immutable layout commands on computational pool val drawCommands = metrics.mapIndexed { index, value -> Point(index * 10f, value) } // Confine actual Skia context mutation to the Main/Render dispatcher withContext(Dispatchers.Main.immediate) { if (!skiaLayer.isClosed) { skiaLayer.needRedraw() // Layer delegate consumes immutable commands safely on the Skiko draw pass skiaLayer.attachRenderer { canvas, width, height -> val paint = Paint().apply { color = Color.RED } for (point in drawCommands) { canvas.drawCircle(point.x, point.y, 5f, paint) } } } } } } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Compose Multiplatform Skiko Render Pipeline Thread-Affinity Guardrail

Compose Multiplatform Skiko Render Pipeline Thread-Affinity Guardrail defines an industrial-grade behavioral standard for mobile engineering. Enforces strict mutation isolation between Kotlin coroutine dispatchers and native Skiko render loops across Compose Multiplatform targets. Prevents fatal native SIGSEGV and EGL/Metal surface crashes during multi-window transitions and configuration changes by restricting surface mutation, context lifecycle, and Skia Canvas operations exclusively to the designated render thread dispatchers. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Dispatching Canvas and Skia Surface Mutations from Asynchronous Default or IO Coroutine Contexts Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Dispatching Canvas and Skia Surface Mutations from Asynchronous Default or IO Coroutine Contexts	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS isolate Skia surface mutations and native Skiko Canvas draws to Skiko's dedicated render thread or `Dispatchers.Main.immediate`.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.