charleswiltgen/axiom-concurrency

Concurrency

You MUST use this skill for ANY concurrency, async/await, threading, or Swift 6 concurrency work.

Quick Reference

| Symptom / Task | Reference | |----------------|-----------| | async/await patterns, @MainActor, actors | See skills/swift-concurrency.md | | Data race errors, Sendable conformance | See skills/swift-concurrency.md | | Swift 6 migration, @concurrent attribute | See skills/swift-concurrency.md | | Actor definition, reentrancy, global actors | See skills/swift-concurrency-ref.md | | Task/TaskGroup/cancellation API | See skills/swift-concurrency-ref.md | | AsyncStream, continuations | See skills/swift-concurrency-ref.md | | DispatchQueue → actor migration | See skills/swift-concurrency-ref.md | | Mutex (iOS 18+), OSAllocatedUnfairLock | See skills/synchronization.md | | Atomic types, lock vs actor decision | See skills/synchronization.md | | MainActor.assumeIsolated | See skills/assume-isolated.md | | @preconcurrency protocol conformances | See skills/assume-isolated.md | | Legacy delegate callbacks | See skills/assume-isolated.md | | Swift Concurrency Instruments template | See skills/concurrency-profiling.md | | Actor contention diagnosis | See skills/concurrency-profiling.md | | Thread pool exhaustion | See skills/concurrency-profiling.md |

Decision Tree

digraph concurrency {
    start [label="Concurrency task" shape=ellipse];
    what [label="What do you need?" shape=diamond];

    start -> what;
    what -> "skills/swift-concurrency.md" [label="async/await, actors,\nSendable, data races,\nSwift 6 migration"];
    what -> "skills/swift-concurrency-ref.md" [label="API syntax lookup\n(TaskGroup, AsyncStream,\ncontinuations, migration)"];
    what -> "skills/synchronization.md" [label="Mutex, locks,\natomic types"];
    what -> "skills/assume-isolated.md" [label="assumeIsolated,\n@preconcurrency"];
    what -> "skills/concurrency-profiling.md" [label="profile async perf,\nactor contention"];
}

1. Data races / actor isolation / @MainActor / Sendable / Swift 6 migration? → skills/swift-concurrency.md 1a. Need specific API syntax (actor definition, TaskGroup, AsyncStream, continuations)? → skills/swift-concurrency-ref.md
2. Writing async/await code? → skills/swift-concurrency.md
3. assumeIsolated / @preconcurrency? → skills/assume-isolated.md
4. Mutex / lock / synchronization? → skills/synchronization.md
5. Profile async performance / actor contention? → skills/concurrency-profiling.md
6. Value type / ARC / generic optimization? → See axiom-performance (skills/swift-performance.md)
7. borrowing / consuming / ~Copyable? → See axiom-swift (skills/ownership-conventions.md)
8. Combine / @Published / AnyCancellable / reactive streams? → See axiom-uikit (skills/combine-patterns.md)
9. Want automated concurrency scan? → concurrency-auditor (Agent)

Concurrency in practice

• HealthKit queries with Swift Concurrency (canonical bridging example) → See axiom-health (skills/queries.md)

Conflict Resolution

concurrency vs axiom-performance: When app freezes or feels slow:

1. Try concurrency FIRST — Main thread blocking is the #1 cause of UI freezes. Check for synchronous work on @MainActor before profiling.
2. Only use axiom-performance if concurrency fixes don't help — Profile after ruling out obvious blocking.

concurrency vs axiom-build: When seeing Swift 6 concurrency errors:

• Use concurrency, NOT axiom-build — Concurrency errors are CODE issues, not environment issues.

concurrency vs axiom-data: When concurrency errors involve Core Data or SwiftData:

• Core Data threading (NSManagedObjectContext thread confinement) → use axiom-data first
• SwiftData + @MainActor ModelContext → use concurrency
• General "background saves losing data" → use axiom-data first

Critical Patterns

Swift Concurrency (skills/swift-concurrency.md):

• Progressive journey: single-threaded → async → concurrent → actors
• @concurrent attribute for forced background execution
• Isolated conformances, main actor mode
• 12 copy-paste patterns including delegate value capture, weak self in Tasks
• Comprehensive decision tree for 7 common error messages

API Reference (skills/swift-concurrency-ref.md):

• Actor definition, reentrancy, global actors, nonisolated
• Sendable patterns, @unchecked Sendable, sending parameter
• Task/TaskGroup/cancellation, async let, withDiscardingTaskGroup
• AsyncStream, continuations, buffering policies
• Isolation patterns (#isolation, @preconcurrency, nonisolated(unsafe))
• DispatchQueue/DispatchGroup/completion handler migration

Synchronization (skills/synchronization.md):

• Mutex (iOS 18+), OSAllocatedUnfairLock (iOS 16+), Atomic types
• Lock vs actor decision tree
• Danger patterns: locks across await, semaphores in async context

Profiling (skills/concurrency-profiling.md):

• Swift Concurrency Instruments template
• Diagnosing main thread blocking, actor contention, thread pool exhaustion
• Safe vs unsafe primitives for cooperative pool

Automated Scanning

Concurrency audit → Launch concurrency-auditor agent or /axiom:audit concurrency (5-phase semantic audit: maps isolation architecture, detects 8 anti-patterns, reasons about missing concurrency patterns, correlates compound risks, scores Swift 6.3 readiness)

Anti-Rationalization

| Thought | Reality | |---------|---------| | "Just add @MainActor and it'll work" | @MainActor has isolation inheritance rules. skills/swift-concurrency.md covers all patterns. | | "I'll use nonisolated(unsafe) to silence the warning" | Silencing warnings hides data races. skills/swift-concurrency.md shows the safe pattern. | | "It's just one async call" | Even single async calls have cancellation and isolation implications. | | "I know how actors work" | Actor reentrancy and isolation rules changed in Swift 6.2. | | "I'll fix the Sendable warnings later" | Sendable violations cause runtime crashes. Fix them now. | | "Combine is dead, just use async/await" | Combine has no deprecation notice. Rewriting working pipelines wastes time. See See axiom-uikit (skills/combine-patterns.md). | | "I'll use @unchecked Sendable to silence this" | You're hiding a data race from the compiler. It will crash in production. | | "This async function runs on a background thread" | async suspends without blocking but resumes on the same actor. Use @concurrent to force background. |

Example Invocations

User: "I'm getting 'data race' errors in Swift 6" → Read: skills/swift-concurrency.md

User: "How do I use @MainActor correctly?" → Read: skills/swift-concurrency.md

User: "How do I create a TaskGroup?" → Read: skills/swift-concurrency-ref.md

User: "What's the AsyncStream API?" → Read: skills/swift-concurrency-ref.md

User: "How do I use assumeIsolated?" → Read: skills/assume-isolated.md

User: "Should I use Mutex or actor?" → Read: skills/synchronization.md

User: "My async code is slow, how do I profile it?" → Read: skills/concurrency-profiling.md

User: "My app is slow due to unnecessary copying" → See axiom-performance (skills/swift-performance.md)

User: "Check my code for Swift 6 concurrency issues" → Invoke: concurrency-auditor agent