Log app exit reasons and memory use

LoopFollow/Application/AppDelegate.swift

@@ -11,6 +11,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
     func application(_: UIApplication, didFinishLaunchingWithOptions _: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
         LogManager.shared.log(category: .general, message: "App started")
         LogManager.shared.cleanupOldLogs()
+        ExitDiagnostics.shared.start()
 
         // Notification and calendar permissions are no longer requested here.
         // They're deferred to the moment the user opts into the feature that
@@ -109,6 +110,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
     }
 
     func applicationWillTerminate(_: UIApplication) {
+        LogManager.shared.log(category: .general, message: "App will terminate (\(ExitDiagnostics.memoryDescription()))")
         #if !targetEnvironment(macCatalyst)
             LiveActivityManager.shared.endOnTerminate()
         #endif

LoopFollow/Helpers/ExitDiagnostics.swift

@@ -0,0 +1,89 @@
+// LoopFollow
+// ExitDiagnostics.swift
+
+import Foundation
+import MetricKit
+import os
+
+/// Logs MetricKit app exit counts and crash diagnostics. iOS delivers these
+/// at most once a day, so a log shared the day after a termination shows why
+/// the process ended.
+final class ExitDiagnostics: NSObject, MXMetricManagerSubscriber {
+    static let shared = ExitDiagnostics()
+
+    func start() {
+        MXMetricManager.shared.add(self)
+    }
+
+    func didReceive(_ payloads: [MXMetricPayload]) {
+        for payload in payloads {
+            guard let exits = payload.applicationExitMetrics else { continue }
+            let range = "\(payload.timeStampBegin) – \(payload.timeStampEnd)"
+
+            let bg = exits.backgroundExitData
+            let background = Self.describe([
+                ("normal", bg.cumulativeNormalAppExitCount),
+                ("memoryLimit", bg.cumulativeMemoryResourceLimitExitCount),
+                ("memoryPressure", bg.cumulativeMemoryPressureExitCount),
+                ("cpuLimit", bg.cumulativeCPUResourceLimitExitCount),
+                ("badAccess", bg.cumulativeBadAccessExitCount),
+                ("illegalInstruction", bg.cumulativeIllegalInstructionExitCount),
+                ("abnormal", bg.cumulativeAbnormalExitCount),
+                ("watchdog", bg.cumulativeAppWatchdogExitCount),
+                ("lockedFile", bg.cumulativeSuspendedWithLockedFileExitCount),
+                ("taskAssertionTimeout", bg.cumulativeBackgroundTaskAssertionTimeoutExitCount),
+            ])
+
+            let fg = exits.foregroundExitData
+            let foreground = Self.describe([
+                ("normal", fg.cumulativeNormalAppExitCount),
+                ("memoryLimit", fg.cumulativeMemoryResourceLimitExitCount),
+                ("badAccess", fg.cumulativeBadAccessExitCount),
+                ("illegalInstruction", fg.cumulativeIllegalInstructionExitCount),
+                ("abnormal", fg.cumulativeAbnormalExitCount),
+                ("watchdog", fg.cumulativeAppWatchdogExitCount),
+            ])
+
+            LogManager.shared.log(category: .general, message: "App exits \(range): background [\(background)], foreground [\(foreground)]")
+        }
+    }
+
+    func didReceive(_ payloads: [MXDiagnosticPayload]) {
+        for payload in payloads {
+            for crash in payload.crashDiagnostics ?? [] {
+                let signal = crash.signal.map { "\($0)" } ?? "-"
+                let exceptionType = crash.exceptionType.map { "\($0)" } ?? "-"
+                let exceptionCode = crash.exceptionCode.map { "\($0)" } ?? "-"
+                let reason = crash.terminationReason ?? "-"
+                LogManager.shared.log(
+                    category: .general,
+                    message: "Crash reported for \(payload.timeStampBegin) – \(payload.timeStampEnd): version=\(crash.applicationVersion), signal=\(signal), exceptionType=\(exceptionType), exceptionCode=\(exceptionCode), terminationReason=\(reason)"
+                )
+            }
+        }
+    }
+
+    /// Current memory footprint and the headroom left before iOS terminates the
+    /// process for exceeding its memory limit.
+    static func memoryDescription() -> String {
+        var info = task_vm_info_data_t()
+        var count = mach_msg_type_number_t(MemoryLayout<task_vm_info_data_t>.size / MemoryLayout<natural_t>.size)
+        let result = withUnsafeMutablePointer(to: &info) {
+            $0.withMemoryRebound(to: integer_t.self, capacity: Int(count)) {
+                task_info(mach_task_self_, task_flavor_t(TASK_VM_INFO), $0, &count)
+            }
+        }
+        let footprint = result == KERN_SUCCESS ? "\(info.phys_footprint / 1_048_576) MB" : "unknown"
+        #if targetEnvironment(macCatalyst)
+            return "memoryFootprint=\(footprint)"
+        #else
+            let available = os_proc_available_memory() / 1_048_576
+            return "memoryFootprint=\(footprint), memoryAvailable=\(available) MB"
+        #endif
+    }
+
+    private static func describe(_ counts: [(String, Int)]) -> String {
+        let nonZero = counts.filter { $0.1 > 0 }
+        return nonZero.isEmpty ? "none" : nonZero.map { "\($0.0)=\($0.1)" }.joined(separator: ", ")
+    }
+}

LoopFollow/ViewControllers/MainViewController.swift

@@ -590,7 +590,7 @@ class MainViewController: UIViewController, UNUserNotificationCenterDelegate {
     @objc func appMovedToBackground() {
         LogManager.shared.log(
             category: .general,
-            message: "App moved to background (refreshType=\(Storage.shared.backgroundRefreshType.value.rawValue), lowPowerMode=\(ProcessInfo.processInfo.isLowPowerModeEnabled), backgroundRefreshStatus=\(Self.describe(UIApplication.shared.backgroundRefreshStatus)))"
+            message: "App moved to background (refreshType=\(Storage.shared.backgroundRefreshType.value.rawValue), lowPowerMode=\(ProcessInfo.processInfo.isLowPowerModeEnabled), backgroundRefreshStatus=\(Self.describe(UIApplication.shared.backgroundRefreshStatus)), \(ExitDiagnostics.memoryDescription()))"
         )
 
         // Allow screen to turn off