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Memory growing?
├─ Progressive growth every minute?
│  └─ Likely retain cycle or timer leak
├─ Spike when action performed?
│  └─ Check if operation runs multiple times
├─ Spike then flat for 30 seconds?
│  └─ Probably normal (collections, caches)
├─ Multiple large spikes stacking?
│  └─ Compound leak (multiple sources)
└─ Can't tell from visual inspection?
   └─ Use Instruments Memory Graph (see below)

1. Open your app in Xcode simulator
2. Click: Debug → Memory Graph Debugger (or icon in top toolbar)
3. Wait for graph to generate (5-10 seconds)
4. Look for PURPLE/RED circles with "⚠" badge
5. Click them → Xcode shows retain cycle chain

✅ Object appears once
❌ Object appears 2+ times (means it's retained multiple times)

PlayerViewModel
  ↑ strongRef from: progressTimer
    ↑ strongRef from: TimerClosure [weak self] captured self
      ↑ CYCLE DETECTED: This creates a retain cycle!

1. Product → Profile (Cmd+I)
2. Select "Memory" template
3. Run scenario that causes memory growth
4. Perform action 5-10 times
5. Check: Does memory line go UP for each action?
   - YES → Leak confirmed
   - NO → Probably not a leak

Time ──→
Memory
   │     ▗━━━━━━━━━━━━━━━━  ← Memory keeps growing (LEAK)
   │    ▄▀
   │   ▄▀
   │  ▄
   └─────────────────────
     Action 1  2  3  4  5

vs normal pattern:

Time ──→
Memory
   │  ▗━━━━━━━━━━━━━━━━━━  ← Memory plateaus (OK)
   │ ▄▀
   │▄
   └─────────────────────
     Action 1  2  3  4  5

// SwiftUI: Check if view disappears cleanly
@main
struct DebugApp: App {
    init() {
        NotificationCenter.default.addObserver(
            forName: NSNotification.Name("UIViewControllerWillDeallocate"),
            object: nil,
            queue: .main
        ) { _ in
            print("✅ ViewController deallocated")
        }
    }
    var body: some Scene { ... }
}

// UIKit: Add deinit logging
class MyViewController: UIViewController {
    deinit {
        print("✅ MyViewController deallocated")
    }
}

// SwiftUI: Use deinit in view models
@MainActor
class ViewModel: ObservableObject {
    deinit {
        print("✅ ViewModel deallocated")
    }
}

1. Add deinit logging above
2. Launch app in Xcode
3. Navigate to view/create ViewModel
4. Navigate away/dismiss
5. Check Console: Do you see "✅ deallocated"?
   - YES → No leak there
   - NO → Object is retained somewhere

import MetricKit

class JetsamMonitor: NSObject, MXMetricManagerSubscriber {
    func didReceive(_ payloads: [MXMetricPayload]) {
        for payload in payloads {
            guard let exitData = payload.applicationExitMetrics else { continue }

            // Background exits (jetsam happens here)
            let bgData = exitData.backgroundExitData

            let jetsamCount = bgData.cumulativeMemoryPressureExitCount
            let memoryLimitCount = bgData.cumulativeMemoryResourceLimitExitCount

            if jetsamCount > 0 {
                print("⚠️ Jetsam kills: \(jetsamCount)")
                // Send to analytics
            }

            if memoryLimitCount > 0 {
                print("⚠️ Memory limit exceeded: \(memoryLimitCount)")
                // This is YOUR app using too much memory
            }
        }
    }
}

class AppDelegate: UIResponder, UIApplicationDelegate {
    func applicationDidEnterBackground(_ application: UIApplication) {
        // 1. Flush state to disk
        saveApplicationState()

        // 2. Clear image caches
        URLCache.shared.removeAllCachedResponses()
        imageCache.removeAllObjects()

        // 3. Release large data structures
        largeDataStore.flush()

        // 4. Clear view controllers not visible
        releaseOffscreenViewControllers()

        // 5. Log memory after cleanup
        logMemoryUsage("Background cleanup complete")
    }

    private func logMemoryUsage(_ context: String) {
        var info = mach_task_basic_info()
        var count = mach_msg_type_number_t(MemoryLayout<mach_task_basic_info>.size) / 4
        let result = withUnsafeMutablePointer(to: &info) {
            $0.withMemoryRebound(to: integer_t.self, capacity: 1) {
                task_info(mach_task_self_, task_flavor_t(MACH_TASK_BASIC_INFO), $0, &count)
            }
        }
        if result == KERN_SUCCESS {
            let memoryMB = Double(info.resident_size) / 1_000_000
            print("📊 [\(context)] Memory: \(String(format: "%.1f", memoryMB))MB")
        }
    }
}

@main
struct MyApp: App {
    @Environment(\.scenePhase) private var scenePhase
    @StateObject private var imageCache = ImageCache()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(imageCache)
        }
        .onChange(of: scenePhase) { _, newPhase in
            if newPhase == .background {
                // Clear caches to reduce jetsam
                imageCache.clearAll()
            }
        }
    }
}

class SceneDelegate: UIResponder, UIWindowSceneDelegate {
    func stateRestorationActivity(for scene: UIScene) -> NSUserActivity? {
        // Save state when backgrounding
        let activity = NSUserActivity(activityType: "com.app.state")
        activity.userInfo = [
            "currentTab": tabController.selectedIndex,
            "scrollPosition": tableView.contentOffset.y,
            "draftText": textField.text ?? ""
        ]
        return activity
    }

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession,
               options connectionOptions: UIScene.ConnectionOptions) {
        // Restore state on launch
        if let activity = connectionOptions.userActivities.first {
            restoreState(from: activity)
        }
    }

    private func restoreState(from activity: NSUserActivity) {
        guard let userInfo = activity.userInfo else { return }

        if let tabIndex = userInfo["currentTab"] as? Int {
            tabController.selectedIndex = tabIndex
        }
        if let scrollY = userInfo["scrollPosition"] as? CGFloat {
            tableView.setContentOffset(CGPoint(x: 0, y: scrollY), animated: false)
        }
        if let draftText = userInfo["draftText"] as? String {
            textField.text = draftText
        }
    }
}

struct ContentView: View {
    @SceneStorage("selectedTab") private var selectedTab = 0
    @SceneStorage("draftText") private var draftText = ""
    @SceneStorage("scrollPosition") private var scrollPosition: Double = 0

    var body: some View {
        TabView(selection: $selectedTab) {
            // Tabs...
        }
    }
}

undefined

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App memory grows while in USE?
├─ YES → Memory leak (fix retention)
└─ NO, but app killed in BACKGROUND → Jetsam (reduce bg memory)

@MainActor
class PlayerViewModel: ObservableObject {
    @Published var currentTrack: Track?
    private var progressTimer: Timer?

    func startPlayback(_ track: Track) {
        currentTrack = track
        // LEAK: Timer.scheduledTimer captures 'self' in closure
        // Even with [weak self], the Timer itself is strong
        progressTimer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { [weak self] _ in
            self?.updateProgress()
        }
        // Timer is never stopped → keeps firing forever
    }

    // Missing: Timer never invalidated
    deinit {
        // LEAK: If timer still running, deinit never called
    }
}

ViewController → strongly retains ViewModel
               ↓
ViewModel → strongly retains Timer
           ↓
Timer → strongly retains closure
        ↓
Closure → captures [weak self] but still holds reference to Timer

@MainActor
class PlayerViewModel: ObservableObject {
    @Published var currentTrack: Track?
    private var progressTimer: Timer?

    func startPlayback(_ track: Track) {
        currentTrack = track
        progressTimer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { [weak self] _ in
            self?.updateProgress()
        }
    }

    func stopPlayback() {
        progressTimer?.invalidate()
        progressTimer = nil  // Important: nil after invalidate
        currentTrack = nil
    }

    deinit {
        progressTimer?.invalidate()  // ← CRITICAL FIX
        progressTimer = nil
    }
}

@MainActor
class PlayerViewModel: ObservableObject {
    @Published var currentTrack: Track?
    private var cancellable: AnyCancellable?

    func startPlayback(_ track: Track) {
        currentTrack = track

        // Timer with Combine - auto-cancels when cancellable is released
        cancellable = Timer.publish(
            every: 1.0,
            tolerance: 0.1,
            on: .main,
            in: .default
        )
        .autoconnect()
        .sink { [weak self] _ in
            self?.updateProgress()
        }
    }

    func stopPlayback() {
        cancellable?.cancel()  // Auto-cleans up
        cancellable = nil
        currentTrack = nil
    }

    // No need for deinit — Combine handles cleanup
}

@MainActor
class PlayerViewModel: ObservableObject {
    @Published var currentTrack: Track?
    private var progressTimer: Timer?

    func startPlayback(_ track: Track) {
        currentTrack = track

        // If progressTimer already exists, stop it first
        progressTimer?.invalidate()
        progressTimer = nil

        progressTimer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { [weak self] _ in
            guard let self = self else {
                // If self deallocated, timer still fires but does nothing
                // Still not ideal - timer keeps consuming CPU
                return
            }
            self.updateProgress()
        }
    }

    func stopPlayback() {
        progressTimer?.invalidate()
        progressTimer = nil
    }

    deinit {
        progressTimer?.invalidate()
        progressTimer = nil
    }
}

func testPlayerViewModelNotLeaked() {
    var viewModel: PlayerViewModel? = PlayerViewModel()
    let track = Track(id: "1", title: "Song")
    viewModel?.startPlayback(track)

    // Verify timer running
    XCTAssertNotNil(viewModel?.progressTimer)

    // Stop and deallocate
    viewModel?.stopPlayback()
    viewModel = nil

    // ✅ Should deallocate without leak warning
}

@MainActor
class PlayerViewModel: ObservableObject {
    init() {
        // LEAK: addObserver keeps strong reference to self
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(handleAudioSessionChange),
            name: AVAudioSession.routeChangeNotification,
            object: nil
        )
        // No matching removeObserver → accumulates listeners
    }

    @objc private func handleAudioSessionChange() { }

    deinit {
        // Missing: Never unregistered
    }
}

@MainActor
class PlayerViewModel: ObservableObject {
    init() {
        NotificationCenter.default.addObserver(
            self,
            selector: #selector(handleAudioSessionChange),
            name: AVAudioSession.routeChangeNotification,
            object: nil
        )
    }

    @objc private func handleAudioSessionChange() { }

    deinit {
        NotificationCenter.default.removeObserver(self)  // ← FIX
    }
}

@MainActor
class PlayerViewModel: ObservableObject {
    private var cancellables = Set<AnyCancellable>()

    init() {
        NotificationCenter.default.publisher(
            for: AVAudioSession.routeChangeNotification
        )
        .sink { [weak self] _ in
            self?.handleAudioSessionChange()
        }
        .store(in: &cancellables)  // Auto-cleanup with viewModel
    }

    private func handleAudioSessionChange() { }

    // No deinit needed - cancellables auto-cleanup
}

@MainActor
class PlayerViewModel: ObservableObject {
    @Published var currentRoute: AVAudioSession.AudioSessionRouteDescription?
    private var cancellables = Set<AnyCancellable>()

    init() {
        NotificationCenter.default.publisher(
            for: AVAudioSession.routeChangeNotification
        )
        .map { _ in AVAudioSession.sharedInstance().currentRoute }
        .assign(to: &$currentRoute)  // Auto-cleanup with publisher chain
    }
}

@MainActor
class PlaylistViewController: UIViewController {
    private var tracks: [Track] = []
    private var updateCallbacks: [(Track) -> Void] = []  // LEAK SOURCE

    func addUpdateCallback() {
        // LEAK: Closure captures 'self'
        updateCallbacks.append { [self] track in
            self.refreshUI(with: track)  // Strong capture of self
        }
        // updateCallbacks grows and never cleared
    }

    // No mechanism to clear callbacks
    deinit {
        // updateCallbacks still references self
    }
}

ViewController
  ↓ strongly owns
updateCallbacks array
  ↓ contains
Closure captures self
  ↓ CYCLE
Back to ViewController (can't deallocate)

@MainActor
class PlaylistViewController: UIViewController {
    private var tracks: [Track] = []
    private var updateCallbacks: [(Track) -> Void] = []

    func addUpdateCallback() {
        updateCallbacks.append { [weak self] track in
            self?.refreshUI(with: track)  // Weak capture
        }
    }

    deinit {
        updateCallbacks.removeAll()  // Clean up array
    }
}

@MainActor
class PlaylistViewController: UIViewController {
    private var updateCallbacks: [(Track) -> Void] = []

    func addUpdateCallback() {
        updateCallbacks.append { [unowned self] track in
            self.refreshUI(with: track)  // Unowned is faster
        }
        // Use unowned ONLY if callback always destroyed before ViewController
    }

    deinit {
        updateCallbacks.removeAll()
    }
}

@MainActor
class PlaylistViewController: UIViewController {
    private var cancellables = Set<AnyCancellable>()

    func addUpdateCallback(_ handler: @escaping (Track) -> Void) {
        // Use PassthroughSubject instead of array
        Just(())
            .sink { [weak self] in
                handler(/* track */)
            }
            .store(in: &cancellables)
    }

    // When done:
    func clearCallbacks() {
        cancellables.removeAll()  // Cancels all subscriptions
    }
}

func testCallbacksNotLeak() {
    var viewController: PlaylistViewController? = PlaylistViewController()
    viewController?.addUpdateCallback { _ in }

    // Verify callback registered
    XCTAssert(viewController?.updateCallbacks.count ?? 0 > 0)

    // Clear and deallocate
    viewController?.updateCallbacks.removeAll()
    viewController = nil

    // ✅ Should deallocate
}

@MainActor
class Player: NSObject {
    var delegate: PlayerDelegate?  // Strong reference
    var onPlaybackEnd: (() -> Void)?  // ← Closure captures self

    init(delegate: PlayerDelegate) {
        self.delegate = delegate
        // LEAK CYCLE:
        // Player → (owns) → delegate
        // delegate → (through closure) → owns → Player
    }
}

class PlaylistController: PlayerDelegate {
    var player: Player?

    override init() {
        super.init()
        self.player = Player(delegate: self)  // Self-reference cycle

        player?.onPlaybackEnd = { [self] in
            // LEAK: Closure captures self
            // self owns player
            // player owns delegate (self)
            // Cycle!
            self.playNextTrack()
        }
    }
}

@MainActor
class PlaylistController: PlayerDelegate {
    var player: Player?

    override init() {
        super.init()
        self.player = Player(delegate: self)

        player?.onPlaybackEnd = { [weak self] in
            // Weak self breaks the cycle
            self?.playNextTrack()
        }
    }

    deinit {
        player?.onPlaybackEnd = nil  // Optional cleanup
        player = nil
    }
}