Kotlin Native ARC-to-GC Reference Cycle Confinement

--- description: Kotlin Native ARC-to-GC Reference Cycle Confinement - Eliminates catastrophic native memory leaks in Kotlin Multiplatform iOS applications caused by cross-runtime retain cycles between Swift ARC and Kotlin Native's Garbage Collector. Because Swift's reference counter cannot trace Kotlin heap allocations and Kotlin's GC treats foreign references as roots, bidirectional object graphs across the bridge must be strictly confined via deterministic weak-reference wrappers and explicit teardown lifecycles. globs: shared/src/iosMain/**/*.kt, shared/src/commonMain/**/*.kt, iosApp/**/*.swift alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/kmp-native-arc-to-gc-cycle-confinement" --- # Kotlin Native ARC-to-GC Reference Cycle Confinement > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Unconfined Bidirectional Strong Retain Cycles Across Swift ARC and Kotlin Native GC Boundaries ## System Constraints You are a Principal Mobile Architect enforcing strict Kotlin Multiplatform (KMP) iOS memory safety rules. Mandate memory boundary invariants between Apple Automatic Reference Counting (ARC) and Kotlin Native Tracing Garbage Collection (GC). Prevent persistent leaks, uncollectable root references, and native OOM crashes across the cinterop boundary. ## Strict Guidelines - Engineers MUST ALWAYS encapsulate Swift delegates and observers in Kotlin's 'iosMain' source set using 'kotlin.native.ref.WeakReference' to prevent holding native ARC roots in the Kotlin GC heap. - Engineers MUST NOT pass Swift instances with strong self-references into Kotlin long-lived singleton registries, Coroutine Job listeners, or StateFlow observers without a deterministic cancellation token. - Swift consumers MUST capture Kotlin object references using '[weak self]' in every completion handler, callback block, or Flow collector bridge. - Kotlin-exported classes that hold Objective-C/Swift delegates MUST provide an explicit 'detach()' or 'close()' lifecycle method that sets native delegate references to null. - UI components (such as UIViewController or SwiftUI Views) MUST cancel active Kotlin Coroutine scopes and nullify bridge listeners inside 'deinit' or 'viewDidDisappear'. ## Bad vs Good Implementations ### Kotlin Native Delegate Holding via WeakReference #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Kotlin holds a strong reference to an Objective-C/Swift delegate. If the Swift delegate holds a reference back to LocationEngineBridge, a cross-runtime cycle is established. Tracing GC treats the Swift object as a live root, and ARC sees a non-zero reference count, causing a permanent native memory leak. ```kotlin // shared/src/iosMain/kotlin/com/example/engine/LocationBridge.kt package com.example.engine import platform.CoreLocation.CLLocationManagerDelegateProtocol import platform.darwin.NSObject class LocationEngineBridge( // VIOLATION: Strong reference to an iOS ARC-managed delegate. // If the Swift delegate retains this LocationEngineBridge, neither // Kotlin GC nor Apple ARC can deallocate either object graph. private val delegate: CLLocationManagerDelegateProtocol ) : NSObject() { fun notifyUpdate(location: String) { delegate.locationManager(null, didUpdateLocations = emptyList<Any?>()) } } ``` #### Production Standard (Correct) > **Standard**: Encapsulating the native delegate inside `kotlin.native.ref.WeakReference` ensures Kotlin GC does not artificially increment ARC retain counts or treat the delegate as an uncollectable GC root. When iOS releases the delegate, the weak reference evaluates to null. ```kotlin // shared/src/iosMain/kotlin/com/example/engine/LocationBridge.kt package com.example.engine import kotlin.native.ref.WeakReference import platform.CoreLocation.CLLocationManagerDelegateProtocol import platform.darwin.NSObject class LocationEngineBridge( delegate: CLLocationManagerDelegateProtocol ) : NSObject() { // CONFINEMENT: Wrap native ARC delegate in a Kotlin WeakReference. private val delegateRef = WeakReference(delegate) fun notifyUpdate(location: String) { val target = delegateRef.get() if (target != null) { target.locationManager(null, didUpdateLocations = emptyList<Any?>()) } else { detach() } } fun detach() { delegateRef.clear() } } ``` ### Swift Flow Collector Cancellation and Weak Self Confinement #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The Kotlin UserViewModel registers the closure in a long-lived scope. The closure strongly captures 'self' (ProfileViewController), while the view controller strongly holds the ViewModel. Neither the view controller nor the ViewModel can ever be deallocated. ```swift // iosApp/iOSApp/Features/UserPresenter.swift import UIKit import SharedKit class ProfileViewController: UIViewController { private let viewModel = UserViewModel() override func viewDidLoad() { super.viewDidLoad() // VIOLATION: Strongly capturing 'self' in Kotlin callback and ignoring Disposable/Closeable viewModel.observeUserState { self.updateUI(state: $0) } } private func updateUI(state: UserState) { // UI updates } } ``` #### Production Standard (Correct) > **Standard**: Explicitly using '[weak self]' breaks ARC retain retention from the Kotlin-exported closure, and invoking 'cancel()' in 'deinit' guarantees deterministic release of the Kotlin Coroutine subscription. ```swift // iosApp/iOSApp/Features/UserPresenter.swift import UIKit import SharedKit class ProfileViewController: UIViewController { private let viewModel = UserViewModel() private var observationWatcher: CancellableWrapper? = nil override func viewDidLoad() { super.viewDidLoad() // CONFINEMENT: Weak self capture and tracking the bridge cancellation handle observationWatcher = viewModel.observeUserState { [weak self] state in guard let self = self else { return } self.updateUI(state: state) } } private func updateUI(state: UserState) { // UI updates } deinit { // Deterministically break cross-runtime retain boundary observationWatcher?.cancel() observationWatcher = nil } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Kotlin Native ARC-to-GC Reference Cycle Confinement

Kotlin Native ARC-to-GC Reference Cycle Confinement defines an industrial-grade behavioral standard for mobile engineering. Eliminates catastrophic native memory leaks in Kotlin Multiplatform iOS applications caused by cross-runtime retain cycles between Swift ARC and Kotlin Native's Garbage Collector. Because Swift's reference counter cannot trace Kotlin heap allocations and Kotlin's GC treats foreign references as roots, bidirectional object graphs across the bridge must be strictly confined via deterministic weak-reference wrappers and explicit teardown lifecycles. 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: Unconfined Bidirectional Strong Retain Cycles Across Swift ARC and Kotlin Native GC Boundaries 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	Unconfined Bidirectional Strong Retain Cycles Across Swift ARC and Kotlin Native GC Boundaries	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 encapsulate Swift delegates and observers in Kotlin's 'iosMain' source set using 'kotlin.native.ref.WeakReference' to prevent holding native ARC roots in the Kotlin GC heap.

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.