Question

我正在解决一些核心数据后台处理的问题。当我保存在我的后台环境中时，它似乎没有将保存推送到主要上下文。调试代码时，我注意到后台线程正在执行保存操作，它似乎停止了（？）这种行为导致我获取过时的对象。

来自保存的Stacktrace：

Thread 29, Queue : NSManagedObjectContext Queue
#0  0x9a5cf80e in semaphore_wait_trap ()
#1  0x02216f08 in _dispatch_thread_semaphore_wait ()
#2  0x02214b3a in _dispatch_barrier_sync_f_slow ()
#3  0x02214a5c in dispatch_barrier_sync_f ()
#4  0x01dfe03b in _perform ()
#5  0x01dfde9e in -[NSManagedObjectContext(_NestedContextSupport) executeRequest:withContext:error:] ()
#6  0x01ddb33c in -[NSManagedObjectContext save:] ()
#7  0x00096213 in __45-[CoreDataHelper saveInManagedObjectContext:]_block_invoke_0 at /Users/peterwarbo/Documents/Projects/MessagePlanr/MessagePlanr/CoreDataHelper.m:307
#8  0x01e734b3 in developerSubmittedBlockToNSManagedObjectContextPerform_privateasync ()

保存方法：

- (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 {

        // First save (child) context
        [context performBlock:^{

            NSError *error = 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();
            }
        }];


        // Then save parent context
        [self.managedObjectContext performBlock:^{

            NSError *error = nil;

            if ([self.managedObjectContext hasChanges] && ![self.managedObjectContext 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();
            }
        }];
    }
}

这是保存的方法，Reminder是NSManagedObject，当操作完成时，我调用完成块。但是在获取一些NSManagedObjects的完成块中它们还没有被更新（由于我假设的保存暂停？）

- (void)checkOverdueRemindersInBackgroundWithCompletionBlock:(void (^)(NSInteger overdueCount, NSArray *reminders))block {

    DLogName()

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

    [syncContext performBlock:^{

        NSArray *reminders = [self fetchEntity:APReminderEntity predicate:nil andSortDescriptors:nil inManagedObjectContext:syncContext];

        NSInteger overdueCount = 0;

        for (Reminder *reminder in reminders) {

            [reminder checkOverdue]; // Checks if object is overdue and sets a flag if it is

            [self saveInManagedObjectContext:syncContext];

            if (reminder.status.intValue == RMReminderStatusOverdue) {

                overdueCount++;
            }

        }

        block(overdueCount, reminders);
    }];
}

threadedManagedObjectContext方法：

- (NSManagedObjectContext *)threadedManagedObjectContext {

    NSManagedObjectContext *threadedMoc = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    threadedMoc.parentContext = self.managedObjectContext; //self.managedObjectContext is of type NSMainQueueConcurrencyType

    return threadedMoc;
}

Answer 1

问题出现了，因为我使用performBlock:异步保存，它立即返回，因此当它返回并调用我的完成块时，保存可能不会被提交。

因此，此问题的答案是在performBlockAndWait:

中运行后台保存流程

现在出现了另一个问题，使用performBlockAndWait:是否有任何缺点？

核心数据后台处理，保存不会推送到主上下文

1 个答案: