axiom-concurrency

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 59e2d18fd914 · 24 Oct 2026Report an issue or request a re-scan

• Publishercharleswiltgen GitHub userOwner of the repository this skill is read from
• Source foldercharleswiltgen/axiom/axiom-codex/skills/axiom-concurrencyThe exact folder we audited
• LicenceMITAs the repository states it
• Commit pinned for this verdict59e2d18fd914A new audit runs when the source changes
• Repository statusNot archivedLast push 3 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: 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.

---
name: axiom-concurrency
description: 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.
license: MIT
---

# Concurrency

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

**Bundled tools on Claude Code:** if `command -v <tool>` finds nothing (hooks off or `--bare`), use `<plugin-root>/tools/<tool>` in place of the bare name; `<plugin-root>` is two levels above this skill's `Base directory for this skill:` path.

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> **Auditors are skills here.** Where this router says "Launch `some-auditor` agent", invoke the
> matching Codex skill instead — same procedure, no Claude Code agent required.
>
> Available: `axiom-audit-concurrency`.
>
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## 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

```dot
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"];
}
```

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`
1b. NotificationCenter observer, `userInfo` casting, or Sendable errors unpacking a notification? → `skills/swift-concurrency-ref.md` (Typed Notifications — `MainActorMessage`/`AsyncMessage`, iOS 26+)
2. Writing async/await code? → `skills/swift-concurrency.md`
3. 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`
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.
3. **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 Swif

Excerpt, first 6,000 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

1. 2026-10-24
   ✓SAFE B 89 / 100

   first audit · source 59e2d18fd914

Questions about axiom-concurrency

• github.com/charleswiltgen/axiom/tree/main/axiom-codex/skills/axi — the audited source at commit 59e2d18fd914 and every finding aboveObserved · 24 Oct 2026

Spotted something wrong? Report a correction · Methodology