Timer Patterns Reference

An API reference for iOS timer mechanisms: Timer, DispatchSourceTimer, Combine's Timer.publish, AsyncTimerSequence from the swift-async-algorithms package, and Task.sleep.

When to Use This Reference

Use this reference when:

• Looking up specific timer API syntax or parameters
• Understanding the DispatchSourceTimer lifecycle state machine
• Deciding between Task.sleep and a repeating timer
• Checking platform availability for timer APIs
• Debugging timer behavior with LLDB commands

Example Prompts

Questions you can ask your assistant that will draw from this reference:

• "What's the API for Timer.publish in Combine?"
• "How do I schedule a DispatchSourceTimer with leeway?"
• "What RunLoop modes are available for Timer?"
• "How do I run a repeating async timer with AsyncTimerSequence?"
• "What's the platform availability for AsyncTimerSequence?"
• "Why won't my selector-based Timer compile inside an async function?"

What's Covered

Timer

• scheduledTimer (block and selector forms), Timer.init with RunLoop.main.add(_:forMode:)
• Which variants are unavailable from async contexts
• tolerance, RunLoop modes (.default, .tracking, .common)
• invalidate() and isValid

DispatchSourceTimer

• makeTimerSource, the .strict flag
• schedule with deadline vs wallDeadline
• Event handlers and breaking retain cycles before cancel()
• activate, suspend, resume, cancel and the state machine's crash rules
• Leeway, and how it is clamped after the first fire

Combine Timer

• Timer.publish, autoconnect(), manual connect()
• Cancellation through AnyCancellable
• ObservableObject integration

AsyncTimerSequence

• The swift-async-algorithms package requirement
• ContinuousClock vs SuspendingClock
• Stopping with task cancellation; background polling

Task.sleep

• One-shot delays vs repeating timers
• Retry with exponential backoff

Debugging and Availability

• LLDB commands for Timer, DispatchSourceTimer and the run loop
• Platform availability matrix

Documentation Scope

This page documents the timer-patterns-ref skill (in the axiom-integration suite), the API reference your assistant uses for timer syntax and lifecycle details. For decision trees, crash patterns and the SafeDispatchTimer wrapper — the "which timer should I use?" questions — see timer-patterns.

Related

• energy – timer tolerance and coalescing as an energy optimization
• energy-ref – timer efficiency APIs with WWDC code examples
• memory-debugging – the timer retain cycle as a memory leak pattern

Resources

Docs: /foundation/timer, /dispatch/dispatchsourcetimer, github.com/apple/swift-async-algorithms