ax-energy

Energy Optimization

Quick Patterns

Power Profiler Workflow (5 min)

1. Connect iPhone wirelessly to Xcode (wireless debugging)
2. Xcode > Product > Profile (Cmd+I)
3. Select Blank template
4. Click "+" > Add "Power Profiler" instrument
5. Optional: Add "CPU Profiler" for correlation
6. Click Record, use app normally for 2-3 minutes
7. Click Stop
8. Expand Power Profiler track, examine per-app lanes:
   - CPU Power Impact: Computation, timers, parsing
   - GPU Power Impact: Animations, blur, Metal
   - Display Power Impact: Brightness, content type
   - Network Power Impact: Requests, downloads, polling

Why wireless: When device is charging via cable, power metrics show 0.

Timer Tolerance (1 min fix)

// BAD: No tolerance, prevents system batching
Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { _ in self.updateUI() }

// GOOD: 10% tolerance for system batching
let timer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { _ in self.updateUI() }
timer.tolerance = 0.1

// BETTER: Combine Timer (auto-cleanup)
Timer.publish(every: 1.0, tolerance: 0.1, on: .main, in: .default)
    .autoconnect()
    .sink { [weak self] _ in self?.refresh() }
    .store(in: &cancellables)

// BEST: Event-driven, no timer
NotificationCenter.default.publisher(for: .dataDidUpdate)
    .sink { [weak self] _ in self?.updateUI() }
    .store(in: &cancellables)

Push vs Poll (100x efficiency)

// BAD: Polling every 5 seconds (radio active 100% of time)
Timer.scheduledTimer(withTimeInterval: 5.0, repeats: true) { [weak self] _ in
    self?.fetchLatestData()
}

// GOOD: Server pushes when data changes
func application(_ application: UIApplication,
                 didReceiveRemoteNotification userInfo: [AnyHashable: Any],
                 fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
    Task {
        do {
            let hasNewData = try await fetchLatestData()
            completionHandler(hasNewData ? .newData : .noData)
        } catch { completionHandler(.failed) }
    }
}