ios - 后台线程中的核心数据锁

Question

我正在锁定 Core Data。我真的不明白原因。因为我在后台线程中处理时正在创建后台 MOC。下面您可以看到发生这种情况时堆栈跟踪(我正在暂停应用程序的执行)的样子:

Thread 1, Queue : com.apple.main-thread

#0  0x32d2a0fc in __psynch_mutexwait ()
#1  0x3608b128 in pthread_mutex_lock ()
#2  0x365d2dac in -[_PFLock lock] ()
#3  0x365e3264 in -[NSPersistentStoreCoordinator executeRequest:withContext:error:] ()
#4  0x365e1e2a in -[NSManagedObjectContext executeFetchRequest:error:] ()
#5  0x3664a93e in -[NSManagedObjectContext(_NestedContextSupport) _parentObjectsForFetchRequest:inContext:error:] ()
#6  0x3664b0c8 in __82-[NSManagedObjectContext(_NestedContextSupport) executeRequest:withContext:error:]_block_invoke_0 ()
#7  0x3932bd28 in _dispatch_barrier_sync_f_slow_invoke ()


Thread 10, Queue : EventKitHelperSyncSerialBackgroundQueue

#0  0x32d19f04 in semaphore_wait_trap ()
#1  0x3932c300 in _dispatch_thread_semaphore_wait$VARIANT$mp ()
#2  0x3932a880 in _dispatch_barrier_sync_f_slow ()
#3  0x3663b9e6 in _perform ()
#4  0x3664adba in -[NSManagedObjectContext(_NestedContextSupport) executeRequest:withContext:error:] ()
#5  0x365e1e2a in -[NSManagedObjectContext executeFetchRequest:error:] ()
#6  0x000b11e4 in -[CoreDataHelper fetchEntity:predicate:andSortDescriptors:inManagedObjectContext:] at /Users/peterwarbo/Desktop/app/CoreDataHelper.m:110
#7  0x000ad648 in -[EventKitHelper processChangedCalendar] at /Users/peterwarbo/Desktop/app/EventKitHelper.m:242
#8  0x000ad3b4 in __54-[EventKitHelper syncInBackgroundWithCompletionBlock:]_block_invoke_0 at /Users/peterwarbo/Desktop/app/EventKitHelper.m:218
#9  0x3932711e in _dispatch_call_block_and_release ()
#10 0x3932aece in _dispatch_queue_drain$VARIANT$mp ()
#11 0x3932adc0 in _dispatch_queue_invoke$VARIANT$mp ()
#12 0x3932b91c in _dispatch_root_queue_drain ()
#13 0x3932bac0 in _dispatch_worker_thread2 ()
#14 0x36090a10 in _pthread_wqthread ()
#15 0x360908a4 in start_wqthread ()

在 EventKitHelperSyncSerialBackgroundQueue 中，我在后台队列中进行一些核心数据处理。 Reminder 是 NSManagedObject。抱歉代码量太大，但我认为最好不要遗漏任何重要细节。

EventKitHelper.m

- (void)syncInBackgroundWithCompletionBlock:(CalendarSyncCompletionBlock)block {

    DLogName()

    self.completionBlock = block;

    if (self.syncSerialBackgroundQueue == NULL) {
        self.syncSerialBackgroundQueue = dispatch_queue_create("EventKitHelperSyncSerialBackgroundQueue", 0);
    }

    dispatch_async(self.syncSerialBackgroundQueue, ^{

        [self processChangedCalendar];
    });
}

- (void)processChangedCalendar {

    DLogName()

    CoreDataHelper *cdHelper = [CoreDataHelper sharedInstance];

    // Store has been changed, events could be updated/deleted/added
    // Need to check if any of the user created Reminders are referencing the calendar
    // If so, update the affected Reminders

    // Predicate to fetch only Reminders that are of type (RMReminderDateServiceCalendarEvent or RMReminderDateServiceCalendarBirthday) AND status is not completed
    NSPredicate *userRemindersPredicate = [NSPredicate predicateWithFormat:@"(dateService == %@ OR dateService == %@) AND status != %@", @(RMReminderDateServiceCalendarEvent), @(RMReminderDateServiceCalendarBirthday), @(RMReminderStatusCompleted)];

    // Sort the user's Reminders with the earliest date first
    NSSortDescriptor *dateSortAsc = [NSSortDescriptor sortDescriptorWithKey:@"date" ascending:YES];

    // Creating a new MOC for thread safety
    NSManagedObjectContext *syncContext = [cdHelper threadedManagedObjectContext];
    self.syncContext = syncContext;

    NSArray *usersReminders = [[CoreDataHelper sharedInstance] fetchEntity:APReminderEntity predicate:userRemindersPredicate andSortDescriptors:@[dateSortAsc] inManagedObjectContext:syncContext];

    if (usersReminders.count == 0) {

        DLog(@"User doesn't have any Calendar Reminders, no need to sync")

        BOOL error = NO;

        self.completionBlock(error);

        return;

    } else {

        if (!self.isCalendarAccessAuthorized) {

            DLog(@"Calendar access is not authorized and we have Calendar Reminders, alert the user")

            BOOL error = YES;

            self.completionBlock(error);

            return;

        } else {

            DLog(@"Calendar access is authorized")
        }
    }

    if (!self.calendarchanged) {

        DLog(@"Calendar not updated, no need to sync")

        BOOL error = NO;

        self.completionBlock(error);

        return;
    }

    DLog(@"Calendar updated, syncing...")

    NSDate *earliestReminderDate = [(Reminder *) [usersReminders objectAtIndex:0] date];

    // Since there exists a possibility that a Calendar event can change date back in time, we should fetch events from our earliest Reminder date + 1 year back

    NSDate *eventsFromThisDate = [Utilities oneYearAgoForDate:[Utilities midnightDateForDate:earliestReminderDate]];

    NSDate *endDate = [NSDate distantFuture]; // This will get me events 4 years from now

    // Create the predicate
    NSPredicate *eventStorePredicate = [self.eventStore predicateForEventsWithStartDate:eventsFromThisDate endDate:endDate calendars:nil];

    // Fetch all events that match the predicate.
    NSArray *eventKitEvents = [self.eventStore eventsMatchingPredicate:eventStorePredicate];

    NSMutableArray *events = [NSMutableArray arrayWithCapacity:100];

    for (EKEvent *event in eventKitEvents) {

        NSString *eventTitle = [event title];
        NSDate *eventDate = [event startDate];
        NSDate *eventDateModified = [event lastModifiedDate];
        NSString *eventID = [event eventIdentifier];

        // Check if event is a Birthday event
        BOOL isBirthday = [event birthdayPersonID] != -1 ? YES : NO;

        RMReminderDateService dateService;

        if (isBirthday) {

            dateService = RMReminderDateServiceCalendarBirthday;

        } else {

            dateService = RMReminderDateServiceCalendarEvent;
        }

        RMDateEvent *calendarEvent = [[RMDateEvent alloc] initWithDate:eventDate
                                                          dateModified:eventDateModified
                                                                  name:eventTitle
                                                           dateService:dateService
                                                                 andID:eventID];

        BOOL eventAlreadyAdded = NO;

        if (!eventAlreadyAdded) {

            [events addObject:calendarEvent];
        }
    }

    for (Reminder *reminder in usersReminders) {

        NSPredicate *predicateID = [NSPredicate predicateWithFormat:@"ID == %@", reminder.dateServiceID];
        NSArray *eventsMatchingID = [events filteredArrayUsingPredicate:predicateID];

        RMDateEvent *event = [eventsMatchingID lastObject];

        if (event == nil) {

            // We couldn't find the event by ID, try to find it by date AND title

            NSPredicate *predicateDateAndTitle = [NSPredicate predicateWithFormat:@"date == %@ AND name == %@", reminder.date, reminder.dateText];

            NSArray *eventsMatchingDateAndTitle = [events filteredArrayUsingPredicate:predicateDateAndTitle];

            event = [eventsMatchingDateAndTitle lastObject];

            if (event == nil) {

                // We couldn't find the event, most likely it has been deleted from the user's events or the user has changed all values for our saved event :-(

            } else {

                // We found it by date AND title                
                [self processReminder:reminder forDateEvent:event];
            }

        } else {

            // We found it by ID
            [self processReminder:reminder forDateEvent:event];
        }
    }

    [self fetchEventsFromNow];
    [self processEventKitEvents];

    #warning TODO: Broadcast a message to update the Reminder date
    AppDelegate *appDelegate = (AppDelegate *) [[UIApplication sharedApplication] delegate];
    [appDelegate setTabCountInBackground];

    self.calendarchanged = NO;

    DLog(@"Calendar sync done")

    BOOL error = NO;

    self.completionBlock(error);
}

- (void)processReminder:(Reminder *)reminder forDateEvent:(RMDateEvent *)event {

    NSDate *eventModifiedDate = [event dateModified];

    if ([eventModifiedDate compare:reminder.dateModified] == NSOrderedDescending) {

        // This event has been modified
        // Most important now is to check if the changed event date has passed
        NSDate *today = [NSDate date];

        if ([today compare:event.date] == NSOrderedDescending) {

            // Event date has passed

            if (reminder.isRepeating) {

                // We cancel the UILocalNotification and reschedule a new UILocalNotification for the next Reminder date status also set to overdue

                NSDate *reminderDate = [Utilities reminderDateFromDate:event.date andTime:reminder.date];

                // Cancel UILocalNotification
                [Utilities cancelUILocalNotificationForReminder:reminder];

                reminder.status = @(RMReminderStatusOverdue);

                reminder.date = reminderDate;
                reminder.dateModified = event.dateModified;
                reminder.dateServiceID = event.ID;
                reminder.dateText = event.name;

                NSDate *nextReminderDate = [Utilities nextReminderDateFromNowForReminder:reminder];
                reminder.date = nextReminderDate;

                // Re-schedule the Reminder
                [Utilities scheduleUILocalNotificationForReminder:reminder];

                // We change back to this old Reminder date to reflect the overdue status
                reminder.date = reminderDate;

                [[CoreDataHelper sharedInstance] saveInManagedObjectContext:self.syncContext];


            } else {

                // We should cancel the UILocalNotification for this Reminder and set the status for this Reminder to overdue

                NSDate *reminderDate = [Utilities reminderDateFromDate:event.date andTime:reminder.date];

                // Cancel UILocalNotification
                [Utilities cancelUILocalNotificationForReminder:reminder];

                reminder.status = @(RMReminderStatusOverdue);

                reminder.date = reminderDate;
                reminder.dateModified = event.dateModified;
                reminder.dateServiceID = event.ID;
                reminder.dateText = event.name;

                [[CoreDataHelper sharedInstance] saveInManagedObjectContext:self.syncContext];
            }

        } else {

            // Event date is in the future

            NSDate *reminderDate = [Utilities reminderDateFromDate:event.date andTime:reminder.date];

            // Cancel UILocalNotification
            [Utilities cancelUILocalNotificationForReminder:reminder];

            reminder.status = @(RMReminderStatusUpcoming);

            reminder.date = reminderDate;
            reminder.dateModified = event.dateModified;
            reminder.dateServiceID = event.ID;
            reminder.dateText = event.name;

            [[CoreDataHelper sharedInstance] saveInManagedObjectContext:self.syncContext];

            // Re-schedule the Reminder
            [Utilities scheduleUILocalNotificationForReminder:reminder];
        }
    }
}

CoreDataHelper.m

- (NSArray *)fetchEntity:(NSString *)entity predicate:(NSPredicate *)predicate andSortDescriptors:(NSArray *)sortDescriptors inManagedObjectContext:(NSManagedObjectContext *)context {

    DLogName()

    if (context == nil) {

        // Use default MOC
        context = self.managedObjectContext;
    }

    NSEntityDescription *entityDescription = [NSEntityDescription entityForName:entity inManagedObjectContext:context];
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    [request setEntity:entityDescription];

    if (predicate != nil) {

        [request setPredicate:predicate];
    }

    if (sortDescriptors != nil) {

        [request setSortDescriptors:sortDescriptors];
    }

    NSError *error = nil;
    NSArray *entities = [context executeFetchRequest:request error:&error];

    if (entities == nil) {

        DLog(@"There was an error: %@", [error userInfo]);
    }

    return entities;
}


- (NSManagedObjectContext *)threadedManagedObjectContext {

    NSManagedObjectContext *threadedMoc = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSConfinementConcurrencyType];
    threadedMoc.parentContext = self.managedObjectContext;

    return threadedMoc;
}

/**
 Returns the managed object context for the application.
 If the context doesn't already exist, it is created and bound to the persistent store coordinator for the application.
 */
- (NSManagedObjectContext *)managedObjectContext {

    if (_managedObjectContext != nil)
    {
        return _managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil)
    {
        //_managedObjectContext = [[NSManagedObjectContext alloc] init];
        _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        [_managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return _managedObjectContext;
}

- (void)saveInManagedObjectContext:(NSManagedObjectContext *)context {

    if (context == nil) {

        // Use default MOC
        context = self.managedObjectContext;

        NSError *error = nil;

        if (context != nil)
        {
            if ([context hasChanges] && ![context save:&error])
            {
                /*
                 Replace this implementation with code to handle the error appropriately.

                 abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                 */
                DLog(@"Unresolved error %@, %@", error, [error userInfo]);
                abort();
            }
        }

    } else {

        NSError *error = nil;

        // First save (child) context
        if ([context hasChanges] && ![context save:&error])
        {
            /*
             Replace this implementation with code to handle the error appropriately.

             abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
             */
            DLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }

        // Then save parent context
        if ([self.managedObjectContext hasChanges])
        {
            /*
             Replace this implementation with code to handle the error appropriately.

             abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
             */

            [self.managedObjectContext performBlock:^{

                NSError *parentError = nil;
                [self.managedObjectContext save:&parentError];

                if (parentError) {

                    DLog(@"Unresolved error %@, %@", parentError, [parentError userInfo]);
                    abort();
                }
            }];
        }
    }
}

Answer 1

不完全确定这是否适用于您，但我遇到了类似的错误。我通过

解决了它们

1. 使用 NSPrivateQueueConcurrencyType 而不是 NSConfinementConcurrencyType 使处理脱离主线程。

2. 将 executeFetchRequest 放入 MOC 的 performBlockAndWait 中。

所以在 CoreDataHelper.m 的 fetchEntity 方法中你会有这样的东西:

[context performBlockAndWait:^{
   NSError *error = nil;
   NSArray *entities = [context executeFetchRequest:request error:&error];
}];