How do I install the Axiom Concurrency skill?

Run npx skillmds@latest add charleswiltgen/axiom-concurrency-2 in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

What does the Axiom Concurrency skill do?

Use when writing ANY async code, actors, or threads in an Apple-platform app, or seeing ANY concurrency error. Covers Swift 6 concurrency, @MainActor, Sendable, data races, async/await patterns. It is listed under Coding & Dev Tools on SkillMD.

Is Axiom Concurrency safe to use?

This skill has not completed SkillMD's automated safety review yet. Independent scanners report: SkillSpector: PASS, Skill Scanner: PASS. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Axiom Concurrency?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Axiom Concurrency free to use?

Yes. Installing skills from SkillMD is free. This skill is licensed under MIT.

Who published Axiom Concurrency?

charleswiltgen (@charleswiltgen) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Axiom Concurrency by charleswiltgen

Name: Axiom Concurrency
Author: charleswiltgen

Concurrency

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

Not on Claude Code? Where this router says "Launch some-auditor agent", read that auditor's file in this suite and follow it inline — the same procedure, needing only file search and read.

Available here: skills/concurrency-auditor.md.

Agents that need Bash — builds, tests, simulators, crash symbolication — stay Claude Code-only; there is no inline equivalent for those.

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`
Warning-free build crashes with `_dispatch_assert_queue_fail`	See `skills/isolation-inheritance-diag.md`
Crash signature `_swift_task_checkIsolatedSwift`	See `skills/isolation-inheritance-diag.md`
Core Data `context.perform` runtime crash inside @MainActor class	See `skills/isolation-inheritance-diag.md`
Combine `.map`/`.sink` crash from receive(on:) placement	See `skills/isolation-inheritance-diag.md`
Delegate method crash from isolation inheritance (CLLocationManager, NSDocument, AVAudioPlayerDelegate, WKNavigationDelegate, PHPhotoLibraryChangeObserver)	See `skills/isolation-inheritance-diag.md`
PhotoKit `performChanges` block traps on PhotoKit's queue	See `skills/isolation-inheritance-diag.md`
Actor reentrancy / stale state across await	See `skills/isolation-inheritance-diag.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/isolation-inheritance-diag.md" [label="warning-free build crashes\n_dispatch_assert_queue_fail\n_swift_task_checkIsolatedSwift"];
    what -> "skills/concurrency-profiling.md" [label="profile async perf,\nactor contention"];
}

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 1b. NotificationCenter observer, userInfo casting, or Sendable errors unpacking a notification? → skills/swift-concurrency-ref.md (Typed Notifications — MainActorMessage/AsyncMessage, iOS 26+)
Writing async/await code? → skills/swift-concurrency.md
assumeIsolated / @preconcurrency? → skills/assume-isolated.md 3a. Warning-free Swift 6 build that crashes in production with _dispatch_assert_queue_fail or _swift_task_checkIsolatedSwift? → skills/isolation-inheritance-diag.md
Mutex / lock / synchronization? → skills/synchronization.md
Profile async performance / actor contention? → skills/concurrency-profiling.md
Value type / ARC / generic optimization? → See axiom-performance (skills/swift-performance.md)
borrowing / consuming / ~Copyable? → See axiom-swift (skills/ownership-conventions.md)
Combine / @Published / AnyCancellable / reactive streams? → See axiom-uikit (skills/combine-patterns.md)
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:

Try concurrency FIRST — Main thread blocking is the #1 cause of UI freezes. Check for synchronous work on @MainActor before profiling.
Only use axiom-performance if concurrency fixes don't help — Profile after ruling out obvious blocking.
To pin a specific freeze to app code, see the Hang Window Workflow in axiom-performance (skills/hang-diagnostics.md) — re-scope xcprof analyze to the hang window with --start-ms/--end-ms --user-binary to surface the app-owned frame on the main thread.

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
GRDB Sendable patterns (struct records, databaseSelection as computed property, Swift 6 conformance) → See axiom-data (skills/grdb-performance.md) §8

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

Runtime Isolation Crashes (skills/isolation-inheritance-diag.md):

_dispatch_assert_queue_fail and _swift_task_checkIsolatedSwift signatures
Closure isolation inheritance (Core Data perform, Combine .map, NotificationCenter .sink)
Delegate method isolation inheritance (CLLocationManager, NSDocument, AVAudioPlayerDelegate, WKNavigationDelegate)
MainActor.assumeIsolated misuse
Actor reentrancy state staleness

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 6.4 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.
"My Swift 6 build has zero warnings, so isolation is correct"	Static checking can't see SDK callbacks. Runtime checks crash anyway. `skills/isolation-inheritance-diag.md`.
"I'll wrap the crash in `MainActor.assumeIsolated`"	`assumeIsolated` is a runtime trap, not a silencer. Wrong assumption = crash.
"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"	Check its isolation, don't assume. A `@MainActor` async function runs entirely on the main actor, and `nonisolated async` runs on the caller's actor under `NonisolatedNonsendingByDefault` (Swift 6.2+; new Xcode projects set `SWIFT_APPROACHABLE_CONCURRENCY = YES`, the setting's own default is NO, and SwiftPM does not enable it) — those are the main-thread freezes. Without that setting `nonisolated async` hops to the global executor. `@concurrent` forces off-actor work either way.

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 warning-free Swift 6 build crashes in production with _dispatch_assert_queue_fail" → Read: skills/isolation-inheritance-diag.md

User: "Core Data context.perform crashes inside an @MainActor view model" → Read: skills/isolation-inheritance-diag.md

User: "CLLocationManager delegate method is crashing with _swift_task_checkIsolatedSwift" → Read: skills/isolation-inheritance-diag.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

Axiom Concurrency

File contents

Concurrency

Quick Reference

Decision Tree

Concurrency in practice

Conflict Resolution

Critical Patterns

Automated Scanning

Anti-Rationalization

Example Invocations

Frequently asked questions

Axiom Concurrency

File contents

Concurrency

Quick Reference

Decision Tree

Concurrency in practice

Conflict Resolution

Critical Patterns

Automated Scanning

Anti-Rationalization

Example Invocations

Related skills

Frequently asked questions

How do I install the Axiom Concurrency skill?

What does the Axiom Concurrency skill do?

Is Axiom Concurrency safe to use?

Which AI agents work with Axiom Concurrency?

Is Axiom Concurrency free to use?

Who published Axiom Concurrency?