add real shutdown for event handler and closing the db

Does not crash as often anymore, but:
- [ ] delay after waking up / unsuspeding, link2xt said probably because of missing cache
- [ ] events are not received by the UI anymore, althrough I sucessfully restarted the handler that the events are printed to the console.
- [ ] there is a performance warning because I wait in the main thread for the event thread to finish: "Thread Performance Checker: Thread running at QOS_CLASS_USER_INTERACTIVE waiting on a lower QoS thread running at QOS_CLASS_BACKGROUND. Investigate ways to avoid priority inversions"

add more logging and add a startio statement

but this didn't fix the issue of the broken state on resume

add reloadDcContext, seems like this fixed the resume issue

do not close db if app is in foreground after fetch

DcCore/DcCore/DC/Wrapper.swift

@@ -18,6 +18,10 @@ public class DcAccounts {
         dc_accounts_unref(accountsPointer)
         accountsPointer = nil
     }
+
+    public func isOpen() -> Bool {
+        return accountsPointer != nil
+    }
 
     public func migrate(dbLocation: String) -> Int {
         return Int(dc_accounts_migrate_account(accountsPointer, dbLocation))

DcShare/Helper/ShareAttachment.swift

@@ -14,7 +14,6 @@ protocol ShareAttachmentDelegate: class {
 }
 
 class ShareAttachment {
-
     weak var delegate: ShareAttachmentDelegate?
     let dcContext: DcContext
     let thumbnailSize = CGFloat(96)

deltachat-ios/AppDelegate.swift

@@ -67,32 +67,21 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
         continueDidFinishLaunchingWithOptions()
         return true
     }
-
-    // finishes the app initialization which depends on the successful access to the keychain
-    func continueDidFinishLaunchingWithOptions() {
-        if let sharedUserDefaults = UserDefaults.shared, !sharedUserDefaults.bool(forKey: UserDefaults.hasSavedKeyToKeychain) {
-            // we can assume a fresh install (UserDefaults are deleted on app removal)
-            // -> reset the keychain (which survives removals of the app) in case the app was removed and reinstalled.
-            if !KeychainManager.deleteDBSecrets() {
-                logger.warning("Failed to delete DB secrets")
-            }
-        }
-
-        do {
-            self.reachability = try Reachability()
-        } catch {
-            // TODO: Handle
-        }
-
+
+    func openAccountsWithKeychain() {
+        logger.info("🔐 openAccountsWithKeychain")
         let accountIds = dcAccounts.getAll()
         for accountId in accountIds {
             let dcContext = dcAccounts.get(id: accountId)
             if !dcContext.isOpen() {
                 do {
+                    logger.info("🔐 start")
                     let secret = try KeychainManager.getAccountSecret(accountID: accountId)
+                    logger.info("🔐 got secret")
                     if !dcContext.open(passphrase: secret) {
                         logger.error("Failed to open database for account \(accountId)")
                     }
+                    logger.info("🔐 done")
                 } catch KeychainError.accessError(let message, let status) {
                     logger.error("Keychain error. \(message). Error status: \(status)")
                     return
@@ -103,7 +92,27 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
                 }
             }
         }
+        logger.info("🔐 openAccountsWithKeychain done")
+    }
 
+    // finishes the app initialization which depends on the successful access to the keychain
+    func continueDidFinishLaunchingWithOptions() {
+        if let sharedUserDefaults = UserDefaults.shared, !sharedUserDefaults.bool(forKey: UserDefaults.hasSavedKeyToKeychain) {
+            // we can assume a fresh install (UserDefaults are deleted on app removal)
+            // -> reset the keychain (which survives removals of the app) in case the app was removed and reinstalled.
+            if !KeychainManager.deleteDBSecrets() {
+                logger.warning("Failed to delete DB secrets")
+            }
+        }
+
+        do {
+            self.reachability = try Reachability()
+        } catch {
+            // TODO: Handle
+        }
+
+        openAccountsWithKeychain()
+
         if dcAccounts.getAll().isEmpty, dcAccounts.add() == 0 {
            fatalError("Could not initialize a new account.")
         }
@@ -211,9 +220,10 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
     // applicationWillEnterForeground() is _not_ called on initial app start
     func applicationWillEnterForeground(_: UIApplication) {
         logger.info("➡️ applicationWillEnterForeground")
+        maybeStart()
         applicationInForeground = true
         dcAccounts.startIo()
-
+        
         DispatchQueue.global(qos: .background).async { [weak self] in
             guard let self = self else { return }
             if let reachability = self.reachability {
@@ -257,6 +267,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
     func applicationDidBecomeActive(_: UIApplication) {
         logger.info("➡️ applicationDidBecomeActive")
         applicationInForeground = true
+        dcAccounts.startIo()
     }
 
     func applicationWillResignActive(_: UIApplication) {
@@ -271,7 +282,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
 
     func applicationWillTerminate(_: UIApplication) {
         logger.info("⬅️ applicationWillTerminate")
-        dcAccounts.closeDatabase()
+        self.closeDB();
         if let reachability = reachability {
             reachability.stopNotifier()
         }
@@ -309,8 +320,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
                 self.unregisterBackgroundTask()
             } else if app.backgroundTimeRemaining < 10 {
                 logger.info("⬅️ few background time, \(app.backgroundTimeRemaining), stopping")
-                self.dcAccounts.stopIo()
-
+                self.closeDB()
                 // to avoid 0xdead10cc exceptions, scheduled jobs need to be done before we get suspended;
                 // we increase the probabilty that this happens by waiting a moment before calling unregisterBackgroundTask()
                 DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
@@ -323,6 +333,34 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
             }
         }
     }
+
+    var shouldShutdownEventLoop: Bool = false
+    var eventShutdownSemaphore = DispatchSemaphore(value: 1)
+    func closeDB() {
+        // add flag to shutdown event handler
+        shouldShutdownEventLoop = true
+        // stopIo will generate atleast one event to the event handler can shut down
+        self.dcAccounts.stopIo()
+        // somehow wait for the eventhandler to be closed
+        eventShutdownSemaphore.wait()
+        // to avoid 0xdead10cc exceptions, we need to make sure there are no locks on files.
+        self.dcAccounts.closeDatabase()
+        shouldShutdownEventLoop = false
+    }
+
+    func maybeStart() {
+        logger.debug("⏫ maybe openDatabase again 🤔")
+        if !dcAccounts.isOpen() {
+            logger.debug("⏫ openDatabase again, because it is closed")
+            dcAccounts.openDatabase(writeable: true)
+            self.openAccountsWithKeychain()
+            logger.debug("⏫ openDatabase done")
+            if !eventHandlerActive {
+                installEventHandler()
+            }
+            reloadDcContext()
+        }
+    }
 
 
     // MARK: - background fetch and notifications
@@ -465,6 +503,8 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
             completionHandler(.newData)
             return
         }
+
+        maybeStart()
 
         // from time to time, `didReceiveRemoteNotification` and `performFetchWithCompletionHandler`
         // are actually called at the same millisecond.
@@ -527,11 +567,10 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
 
             if !self.appIsInForeground() {
                 self.dcAccounts.stopIo()
+                // to avoid 0xdead10cc exceptions, we need to make sure there are no locks on files.
+                self.closeDB()
             }
 
-            // to avoid 0xdead10cc exceptions, scheduled jobs need to be done before we get suspended;
-            // we increase the probabilty that this happens by waiting a moment before calling completionHandler()
-            usleep(1_000_000)
             logger.info("⬅️ fetch done")
             completionHandler(.newData)
             if backgroundTask != .invalid {
@@ -597,16 +636,24 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
         }
     }
 
+    var eventHandlerActive = false
     func installEventHandler() {
         DispatchQueue.global(qos: .background).async { [weak self] in
             guard let self = self else { return }
             let eventHandler = DcEventHandler(dcAccounts: self.dcAccounts)
             let eventEmitter = self.dcAccounts.getEventEmitter()
+            eventHandlerActive = true
+            logger.info("⏫ event emitter started")
             while true {
+                if shouldShutdownEventLoop {
+                    break
+                }
                 guard let event = eventEmitter.getNextEvent() else { break }
                 eventHandler.handleEvent(event: event)
             }
-            logger.info("⬅️ event emitter finished")
+            logger.info("⏬ event emitter finished")
+            eventShutdownSemaphore.signal()
+            eventHandlerActive = false
         }
     }