mirror of
https://github.com/CharlesWiltgen/Axiom.git
synced 2026-09-20 19:58:20 +08:00
Charles Wiltgen
6586852dc9
Adds the synchronous withTaskCancellationShield overload and hasActiveCancellationShield (static on Task, instance on UnsafeCurrentTask). A runtime probe on macOS 27 established what the interface does not state: the shield MASKS cancellation rather than suppressing throws. Inside a shield, in a cancelled task, Task.isCancelled reads false, checkCancellation() does not throw, and Task.sleep completes. The trap follows directly and is now the headline: a "while !Task.isCancelled" loop inside a shield never exits — the condition it polls is the one the shield suppresses. An onCancel registered inside a shield likewise does not fire for an already-pending cancellation. Also measured: nesting is safe (inner pop leaves the outer installed); masking is scoped to the region, so a child outliving the shield sees isCancelled == true — shielding a spawn does not permanently detach it; and hasActiveCancellationShield is per-task, not per-region, so a structured child reports false while still observing isCancelled == false. Closes Axiom-csr.
3.0 KiB
3.0 KiB
Swift Concurrency Reference
Complete API reference for Swift's concurrency model — actors, Sendable, Task management, async sequences, continuations, and migration patterns from GCD.
When to Use This Reference
Use this reference when:
- Looking up actor definition syntax or reentrancy rules
- Implementing Sendable conformance for your types
- Creating TaskGroups for parallel work
- Working with AsyncStream or custom AsyncSequence
- Bridging callback-based APIs with continuations
- Migrating from DispatchQueue/DispatchGroup to actors/TaskGroup
Example Prompts
- "How do I create a TaskGroup in Swift?"
- "What's the AsyncStream continuation API?"
- "How do I make a custom global actor?"
- "How do I convert a completion handler to async/await?"
- "What are the actor reentrancy rules?"
- "How do I make my class Sendable?"
- "What's the difference between Task and Task.detached?"
- "How do I run a block that ignores task cancellation?" (iOS 27)
- "Why does my loop never exit inside
withTaskCancellationShield?" (iOS 27)
What's Covered
- Actor patterns (definition, nonisolated, reentrancy, global actors, gotcha table)
- Sendable patterns (struct/enum, @Sendable closures, @unchecked, conditional, gotcha table)
- Task management (Task, Task.detached, cancellation,
withTaskCancellationShieldandhasActiveCancellationShield(iOS 27), priority, @TaskLocal, gotcha table) - Structured concurrency (async let, TaskGroup, task tree semantics, gotcha table)
- Async sequences (AsyncStream, continuation API, buffering, custom AsyncSequence, gotcha table)
- Isolation patterns (@MainActor, nonisolated, #isolation, sending, gotcha table)
- Continuations (withCheckedContinuation, resume-exactly-once, bridging, gotcha table)
- Migration patterns (DispatchQueue to actor, DispatchGroup to TaskGroup, callbacks to async, gotcha table)
- Typed notifications (
MainActorMessage/AsyncMessage, iOS 26+ — replacinguserInfocasting, observation-token lifetime, per-framework coverage) - API quick reference table with Swift version requirements
Documentation Scope
This page documents the axiom-concurrency (swift-concurrency-ref reference) — the API reference Claude uses for Swift concurrency syntax and patterns.
For the progressive journey and decision trees: See Swift Concurrency for when and why to introduce concurrency, plus 11 copy-paste patterns.
Related
- Swift Concurrency – Progressive journey from single-threaded to concurrent code, decision trees, @concurrent and isolated conformances
- Synchronization – Mutex, OSAllocatedUnfairLock, atomic types (when you need locks instead of actors)
- assumeIsolated – Synchronous actor access patterns
- Concurrency Profiling – Instruments workflows for async performance
Resources
WWDC: 2021-10132, 2021-10134, 2022-110350, 2025-268
Skills: axiom-concurrency