ios-chaos-monkey

iOS Chaos Monkey — Crash-Hunter Best Practices Adversarial crash-hunting guide for iOS and Swift applications. Contains 47 rules across 8 categories, prioritized by crash severity. Every rule follows TDD: dangerous code first, a failing test that proves the bug, then the fix that makes the test pass. Clinic Architecture Contract (iOS 26 / Swift 6.2) All guidance in this skill assumes the clinic modular MVVM-C architecture: Feature modules import Domain + DesignSystem only (never Data , never sibling features) App target is the convergence point and owns DependencyContainer , concrete coordinators, and Route Shell wiring Domain stays pure Swift and defines models plus repository, *Coordinating , ErrorRouting , and AppError contracts Data owns SwiftData/network/sync/retry/background I/O and implements Domain protocols Read/write flow defaults to stale-while-revalidate reads and optimistic queued writes ViewModels call repository protocols directly (no default use-case/interactor layer) When to Apply Reference these guidelines when: Hunting data races, deadlocks, and concurrency crashes in Swift Auditing memory management for retain cycles and use-after-free Reviewing async/await code for cancellation and continuation leaks Stress-testing file I/O and CoreData/SwiftData persistence layers Writing proof-of-crash tests before implementing fixes Rule Categories by Priority Priority Category Impact Prefix 1 Data Races & Thread Safety CRITICAL race- 2 Memory Corruption & Leaks CRITICAL mem- 3 Deadlocks & Thread Starvation HIGH dead- 4 Async/Await & Structured Concurrency HIGH async- 5 File I/O & Persistence Corruption MEDIUM-HIGH io- 6 Collection & State Mutation MEDIUM mut- 7 Resource Exhaustion MEDIUM exhaust- 8 Objective-C Interop Traps LOW-MEDIUM objc- Quick Reference 1. Data Races & Thread Safety (CRITICAL) race-dictionary-concurrent-write - Concurrent Dictionary mutation crashes with EXC_BAD_ACCESS race-array-concurrent-append - Concurrent Array append corrupts internal buffer race-property-access - Unsynchronized property read-write across threads race-lazy-initialization - Lazy property double-initialization under concurrency race-singleton-initialization - Non-atomic singleton exposes partially constructed state race-bool-flag - Non-atomic Bool flag creates check-then-act race race-closure-capture-mutation - Closure captures mutable reference across threads race-delegate-nilification - Delegate set to nil during active callback 2. Memory Corruption & Leaks (CRITICAL) mem-closure-retain-cycle - Strong self capture in escaping closures creates retain cycle mem-timer-retain-cycle - Timer retains target creating undiscoverable retain cycle mem-delegate-strong-reference - Strong delegate reference prevents deallocation mem-unowned-crash - Unowned reference crashes after owner deallocation mem-notification-observer-leak - NotificationCenter observer retains closure after removal needed mem-combine-sink-retain - Combine sink retains self without cancellable storage mem-async-task-self-capture - Task captures self extending lifetime beyond expected scope 3. Deadlocks & Thread Starvation (HIGH) dead-sync-on-main - DispatchQueue.main.sync from main thread deadlocks instantly dead-recursive-lock - Recursive lock acquisition on same serial queue dead-actor-reentrancy - Actor reentrancy produces unexpected interleaving dead-semaphore-in-async - Semaphore.wait() inside async context deadlocks thread pool dead-queue-hierarchy - Dispatch queue target hierarchy inversion deadlocks dead-mainactor-blocking - Blocking MainActor with synchronous heavy work 4. Async/Await & Structured Concurrency (HIGH) async-missing-cancellation - Missing Task.isCancelled check wastes resources after navigation async-detached-task-leak - Detached task without cancellation handle leaks work async-task-group-error - TaskGroup silently drops child task errors async-continuation-leak - CheckedContinuation never resumed leaks awaiting task async-actor-hop-starvation - Excessive MainActor hops in hot loop starve UI updates async-unsafe-sendable - @unchecked Sendable hides data race from compiler 5. File I/O & Persistence Corruption (MEDIUM-HIGH) io-concurrent-file-write - Concurrent file writes corrupt data without coordination io-coredata-cross-thread - CoreData NSManagedObject accessed from wrong thread io-swiftdata-background - SwiftData model accessed from wrong ModelContext io-plist-concurrent-mutation - UserDefaults concurrent read-write produces stale values io-filemanager-race - FileManager existence check then use is a TOCTOU race io-keychain-thread-safety - Keychain access from multiple threads returns unexpected errors 6. Collection & State Mutation (MEDIUM) mut-enumerate-and-mutate - Collection mutation during enumeration crashes at runtime mut-kvo-dealloc-crash - KVO observer not removed before deallocation crashes mut-index-out-of-bounds - Array index access without bounds check crashes mut-force-unwrap - Force unwrapping optional in production crashes on nil mut-enum-future-cases - Non-exhaustive switch crashes on unknown enum case 7. Resource Exhaustion (MEDIUM) exhaust-unbounded-task-spawn - Unbounded task spawning in loop exhausts memory exhaust-thread-explosion - GCD creates unbounded threads under concurrent load exhaust-urlsession-leak - URLSession not invalidated leaks delegate and connections exhaust-file-descriptor-leak - File handle not closed leaks file descriptors exhaust-memory-warning-ignored - Low memory warning ignored triggers Jetsam kill 8. Objective-C Interop Traps (LOW-MEDIUM) objc-unrecognized-selector - Missing @objc annotation crashes with unrecognized selector objc-nsnull-in-json - NSNull in decoded JSON collection crashes on access objc-bridge-type-mismatch - Swift/ObjC bridge type mismatch crashes at runtime objc-dynamic-dispatch - Missing dynamic keyword breaks method swizzling How to Use Read individual reference files for detailed explanations and code examples: Section definitions - Category structure and impact levels Rule template - Template for adding new rules Reference Files File Description references/_sections.md Category definitions and ordering assets/templates/_template.md Template for new rules metadata.json Version and reference information