use core background fetch, use .default qos

DcCore/DcCore/DC/events.swift

@@ -156,9 +156,6 @@ public class DcEventHandler {
             }
 
         case DC_EVENT_CONNECTIVITY_CHANGED:
-            if let sem = dcAccounts.fetchSemaphore, dcAccounts.isAllWorkDone() {
-                sem.signal()
-            }
             if accountId != dcAccounts.getSelected().id {
                 return
             }
@@ -167,6 +164,11 @@ public class DcEventHandler {
                 NotificationCenter.default.post(name: eventConnectivityChanged, object: nil)
             }
 
+        case DC_EVENT_ACCOUNTS_BACKGROUND_FETCH_DONE:
+            if let sem = dcAccounts.fetchSemaphore {
+                sem.signal()
+            }
+
         case DC_EVENT_WEBXDC_STATUS_UPDATE:
             if accountId != dcAccounts.getSelected().id {
                 return

DcShare/Helper/ShareAttachment.swift

@@ -138,7 +138,7 @@ class ShareAttachment {
                 _ = self.addDcMsg(path: url.relativePath, viewType: DC_MSG_VIDEO)
                 self.delegate?.onAttachmentChanged()
                 if self.imageThumbnail == nil {
-                    DispatchQueue.global(qos: .background).async {
+                    DispatchQueue.global().async {
                         self.imageThumbnail = DcUtils.generateThumbnailFromVideo(url: url)
                         DispatchQueue.main.async {
                             self.delegate?.onThumbnailChanged()

deltachat-ios/AppDelegate.swift

@@ -132,7 +132,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
                 // maybeNetwork() shall not be called in ui thread;
                 // Reachability::reachabilityChanged uses DispatchQueue.main.async only
                 logger.info("network: reachable \(reachability.connection.description)")
-                DispatchQueue.global(qos: .background).async { [weak self] in
+                DispatchQueue.global().async { [weak self] in
                     guard let self else { return }
                     self.dcAccounts.maybeNetwork()
                     if self.notifyToken == nil &&
@@ -145,7 +145,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
 
             reachability.whenUnreachable = { _ in
                 logger.info("network: not reachable")
-                DispatchQueue.global(qos: .background).async { [weak self] in
+                DispatchQueue.global().async { [weak self] in
                     self?.dcAccounts.maybeNetworkLost()
                 }
             }
@@ -233,7 +233,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
         applicationInForeground = true
         dcAccounts.startIo()
 
-        DispatchQueue.global(qos: .background).async { [weak self] in
+        DispatchQueue.global().async { [weak self] in
             guard let self else { return }
             if let reachability = self.reachability {
                 if reachability.connection != .unavailable {
@@ -484,35 +484,32 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
         pushToDebugArray("1")
 
         // move work to non-main thread to not block UI (otherwise, in case we get suspended, the app is blocked totally)
-        // (we are using `qos: default` as `qos: .background` or `main.asyncAfter` may be delayed by tens of minutes)
+        // (we are using `qos: default` as `qos: .background` may be delayed by tens of minutes)
         DispatchQueue.global().async { [weak self] in
             guard let self else { completionHandler?(.failed); return }
 
-            // we're in background, run IO for a little time
-            self.dcAccounts.startIo()
-            self.dcAccounts.maybeNetwork()
             self.pushToDebugArray("2")
 
             self.addDebugFetchTimestamp()
-
-            // create a new semaphore to make sure the received DC_CONNECTIVITY_CONNECTED really belongs to maybeNetwork() from above
-            // (maybeNetwork() sets connectivity to DC_CONNECTIVITY_CONNECTING, when fetch is done, we're back at DC_CONNECTIVITY_CONNECTED)
             self.dcAccounts.fetchSemaphore = DispatchSemaphore(value: 0)
+            let start = CFAbsoluteTimeGetCurrent()
+
+            // backgroundFetch() pauses IO as needed
+            if !self.dcAccounts.backgroundFetch(timeout: 20) {
+                logger.error("backgroundFetch failed")
+                self.pushToDebugArray("ERR2")
+            }
+            let diff = CFAbsoluteTimeGetCurrent() - start
+
+            // wait for DC_EVENT_ACCOUNTS_BACKGROUND_FETCH_DONE;
+            // without IO being started, more events that could interfere with shutdown are not added
             _ = self.dcAccounts.fetchSemaphore?.wait(timeout: .now() + 20)
             self.dcAccounts.fetchSemaphore = nil
+            let diff2 = CFAbsoluteTimeGetCurrent() - start
 
-            // TOCHECK: it seems, we are not always reaching this point in code,
-            // semaphore?.wait() does not always exit after the given timeout and the app gets suspended -
-            // maybe that is on purpose somehow to suspend inactive apps, not sure.
-            // this does not happen often, but still.
-            // cmp. https://github.com/deltachat/deltachat-ios/pull/1542#pullrequestreview-951620906
-            logger.info("⬅️ finishing fetch")
+            logger.info("⬅️ finishing fetch in \(diff) s + \(diff2) s")
             self.pushToDebugArray(String(format: "3/%.3fs", Double(Date().timeIntervalSince1970)-nowTimestamp))
 
-            if !self.appIsInForeground() {
-                self.dcAccounts.stopIo()
-            }
-
             // 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)
@@ -590,7 +587,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
             return
         }
         eventHandlerActive = true
-        DispatchQueue.global(qos: .background).async { [weak self] in
+        DispatchQueue.global().async { [weak self] in
             guard let self else { return }
             let eventHandler = DcEventHandler(dcAccounts: self.dcAccounts)
             let eventEmitter = self.dcAccounts.getEventEmitter()

deltachat-ios/Chat/ChatViewController.swift

@@ -525,7 +525,7 @@ class ChatViewController: UITableViewController, UITableViewDropDelegate {
 
         // things that do not affect the chatview
         // and are delayed after the view is displayed
-        DispatchQueue.global(qos: .background).async { [weak self] in
+        DispatchQueue.global().async { [weak self] in
             guard let self else { return }
             self.dcContext.marknoticedChat(chatId: self.chatId)
         }
@@ -959,7 +959,7 @@ class ChatViewController: UITableViewController, UITableViewDropDelegate {
            let indexPaths = tableView.indexPathsForVisibleRows {
                 let visibleMessagesIds = indexPaths.map { UInt32(messageIds[$0.row]) }
                 if !visibleMessagesIds.isEmpty {
-                    DispatchQueue.global(qos: .background).async { [weak self] in
+                    DispatchQueue.global().async { [weak self] in
                         self?.dcContext.markSeenMessages(messageIds: visibleMessagesIds)
                     }
                 }

deltachat-ios/Controller/ConnectivityViewController.swift

@@ -25,7 +25,7 @@ class ConnectivityViewController: WebViewViewController {
                 self.loadHtml()
             }
             isLowDataMode = monitor.currentPath.isConstrained
-            monitor.start(queue: DispatchQueue.global(qos: .background))
+            monitor.start(queue: DispatchQueue.global())
             self.connectivityMonitor = monitor
         }
     }

deltachat-ios/DC/DcAccount.swift

@@ -59,10 +59,6 @@ public class DcAccounts {
         dc_accounts_maybe_network_lost(accountsPointer)
     }
 
-    public func isAllWorkDone() -> Bool {
-        return dc_accounts_all_work_done(accountsPointer) != 0
-    }
-
     public func startIo() {
         dc_accounts_start_io(accountsPointer)
     }
@@ -71,6 +67,10 @@ public class DcAccounts {
         dc_accounts_stop_io(accountsPointer)
     }
 
+    public func backgroundFetch(timeout: UInt64) -> Bool {
+        return dc_accounts_background_fetch(accountsPointer, timeout) == 1
+    }
+
     public func select(id: Int) -> Bool {
         return dc_accounts_select_account(accountsPointer, UInt32(id)) == 1
     }

deltachat-ios/Extensions/UIImageView+Extensions.swift

@@ -6,7 +6,7 @@ extension UIImageView {
     func loadVideoThumbnail(from url: URL, placeholderImage: UIImage?, completionHandler: ((UIImage?) -> Void)?) {
 
         self.image = placeholderImage
-        DispatchQueue.global(qos: .background).async {
+        DispatchQueue.global().async {
             let thumbnailImage = DcUtils.generateThumbnailFromVideo(url: url)
             DispatchQueue.main.async { [weak self] in
                 self?.image = thumbnailImage

deltachat-ios/Handler/DeviceContactsHandler.swift

@@ -42,7 +42,7 @@ class DeviceContactsHandler {
 
     private func fetchContactsWithEmailFromDevice(completionHandler: @escaping ([CNContact]) -> Void) {
 
-        DispatchQueue.global(qos: .background).async {
+        DispatchQueue.global().async {
             let keys = [CNContactFamilyNameKey, CNContactGivenNameKey, CNContactEmailAddressesKey]
 
             var fetchedContacts: [CNContact] = []

deltachat-ios/Helper/FileHelper.swift

@@ -63,7 +63,7 @@ public class FileHelper {
 
     public static func deleteFile(atPath: String?) {
         if Thread.isMainThread {
-            DispatchQueue.global(qos: .background).async {
+            DispatchQueue.global().async {
                 deleteFile(atPath)
             }
         } else {

deltachat-ios/Helper/NotificationManager.swift

@@ -42,7 +42,7 @@ public class NotificationManager {
     }
 
     public static func removeNotificationsForChat(dcContext: DcContext, chatId: Int) {
-        DispatchQueue.global(qos: .background).async {
+        DispatchQueue.global().async {
             NotificationManager.removePendingNotificationsFor(dcContext: dcContext, chatId: chatId)
             NotificationManager.removeDeliveredNotificationsFor(dcContext: dcContext, chatId: chatId)
             NotificationManager.updateApplicationIconBadge()
@@ -70,7 +70,7 @@ public class NotificationManager {
                 logger.info("notification background task will end soon")
             }
 
-            DispatchQueue.global(qos: .background).async { [weak self] in
+            DispatchQueue.global().async { [weak self] in
                 guard let self else { return }
                 if let ui = notification.userInfo,
                    let chatId = ui["chat_id"] as? Int,