Timer Safety Patterns

Production-safe timer patterns preventing DispatchSourceTimer crashes and RunLoop mode gotchas.

When to Use

Use this skill when:

• Timer stops firing during scrolling
• EXC_BAD_INSTRUCTION crash in timer code
• Choosing between Timer, DispatchSourceTimer, Combine, or async timer APIs
• Implementing a repeating timer with proper lifecycle management

Example Prompts

• "My timer stops when the user scrolls the list"
• "I'm getting EXC_BAD_INSTRUCTION in my DispatchSourceTimer code"
• "Should I use Timer or DispatchSourceTimer?"
• "How do I safely cancel a DispatchSourceTimer?"
• "What's the best timer API for a background polling task?"

What This Skill Provides

• Timer vs DispatchSourceTimer vs Combine vs AsyncTimerSequence decision tree
• The 4 DispatchSourceTimer crash patterns (each causes EXC_BAD_INSTRUCTION) with safe alternatives
• RunLoop mode explanation (why .default breaks during scrolling)
• Copy-paste SafeDispatchTimer wrapper class with state machine
• 6 anti-patterns with time costs
• 3 pressure scenarios for deadline resistance

Related

• Timer Patterns Reference — API reference for all timer APIs with lifecycle diagrams and platform availability
• Memory Debugging — Timer as Pattern 1 memory leak (Timer retains target)
• Energy Optimization — Timer tolerance and energy-efficient scheduling

Resources

WWDC: 2017-706

Skills: axiom-timer-patterns-ref, axiom-memory-debugging, axiom-energy