ios – 具有多个线程的CoreData死锁

我遇到了多个NsmanagedObjectContexts&多线程场景.在我的一些视图控制器中,我的应用程序使用后台线程从Web服务获取数据,并在同一个线程中保存它.在其他情况下,在没有保存的情况下不进一步进展是有意义的(例如,当他们点击“下一步”时表单中的持久值),保存在主线程上完成. AFAIK在理论上应该没有任何问题,但偶尔我可以在调用时发生死锁

if (![moc save:&error])

…当发生死锁时,这似乎总是在后台线程的保存中.每次通话都不会发生;事实上它完全相反,我必须使用我的应用程序几分钟然后它会发生.

我已经阅读了我能找到的所有帖子以及Apple文档等,我确信我正在遵循这些建议.具体而言,我对使用多个MOC /线程的理解归结为：

>每个线程必须有自己的MOC.
>必须在该线程上创建线程的MOC(不从一个线程传递到另一个线程).
>无法传递NsmanagedObject,但NsmanagedObjectID可以,并且您使用该ID使用不同的MOC来扩充NsmanagedObject.
>如果@L_760_2@mOC的更改都使用相同的PersistentStoreCoordinator,则必须将其合并到另@L_760_2@mOC.

不久之前,我在this SO thread上遇到了MOC助手类的一些代码,发现它很容易理解并且使用起来非常方便,因此我所有的MOC交互都是通过它进行的.这是我的ManagedObjectContextHelper类的完整内容：

#import "ManagedObjectContextHelper.h"

@implementation ManagedObjectContextHelper

+(void)initialize {
    [[NsnotificationCenter defaultCenter] addObserver:[self class]
                                             SELEctor:@SELEctor(threadExit:)
                                                 name:NSThreadWillExitNotification
                                               object:nil];
}

+(void)threadExit:(Nsnotification *)aNotification {
    TDAppDelegate *delegate = (TDAppDelegate *)[[UIApplication sharedApplication] delegate];
    NSString *threadKey = [NSString StringWithFormat:@"%p",[NSThread currentThread]];
    NSMutableDictionary *managedObjectContexts = delegate.managedObjectContexts;

    [managedObjectContexts removeObjectForKey:threadKey];
}

+(NsmanagedObjectContext *)managedObjectContext {
    TDAppDelegate *delegate = (TDAppDelegate *)[[UIApplication sharedApplication] delegate];
    NsmanagedObjectContext *moc = delegate.managedObjectContext;

    NSThread *thread = [NSThread currentThread];

    if ([thread ismainThread]) {
        [moc setMergePolicy:NSErrorMergePolicy];
        return moc;
    }

    // a key to cache the context for the given thread
    NSString *threadKey = [NSString StringWithFormat:@"%p",thread];

    // delegate.managedObjectContexts is a mutable Dictionary in the app delegate
    NSMutableDictionary *managedObjectContexts = delegate.managedObjectContexts;

    if ( [managedObjectContexts objectForKey:threadKey] == nil ) {
        // create a context for this thread
        NsmanagedObjectContext *thReadContext = [[NsmanagedObjectContext alloc] init];
        [thReadContext setPersistentStoreCoordinator:[moc persistentStoreCoordinator]];
        [thReadContext setMergePolicy:NSErrorMergePolicy];
        // cache the context for this thread
        NSLog(@"Adding a new thread:%@",threadKey);
        [managedObjectContexts setObject:thReadContext forKey:threadKey];
    }

    return [managedObjectContexts objectForKey:threadKey];
}

+(void)commit {
    // get the moc for this thread
    NsmanagedObjectContext *moc = [self managedObjectContext];

    NSThread *thread = [NSThread currentThread];

    if ([thread ismainThread] == NO) {
        // only observe notifications other than the main thread
        [[NsnotificationCenter defaultCenter] addObserver:[self class]                                                 SELEctor:@SELEctor(contextDidSave:)
                                                     name:NsmanagedObjectContextDidSaveNotification
                                                   object:moc];
    }

    NSError *error;
    if (![moc save:&error]) {
        NSLog(@"Failure is happening on %@ thread",[thread ismainThread]?@"main":@"other");

        NSArray* detailedErrors = [[error userInfo] objectForKey:NSDetailedErrorsKey];
        if(detailedErrors != nil && [detailedErrors count] > 0) {
            for(NSError* detailedError in detailedErrors) {
                NSLog(@"  DetailedError: %@",[detailedError userInfo]);
            }
        }
        NSLog(@"  %@",[error userInfo]);

    }

    if ([thread ismainThread] == NO) {
        [[NsnotificationCenter defaultCenter] removeObserver:[self class]                                                        name:NsmanagedObjectContextDidSaveNotification
                                                      object:moc];
    }
}

+(void)contextDidSave:(Nsnotification*)saveNotification {
    TDAppDelegate *delegate = (TDAppDelegate *)[[UIApplication sharedApplication] delegate];
    NsmanagedObjectContext *moc = delegate.managedObjectContext;

    [moc performSELEctorOnMainThread:@SELEctor(mergeChangesFromContextDidSaveNotification:)
                          withObject:saveNotification
                       waitUntilDone:NO];
}
@end

这是多线程位的片段,它似乎在死锁：

NsmanagedObjectID *parentObjectID = [parent objectID];

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,0ul);
    dispatch_async(queue,^{
        // GET BACKGROUND MOC
        NsmanagedObjectContext *BACkgroundContext = [ManagedObjectContextHelper managedObjectContext];

        Parent *BACkgroundParent = (Parent*)[BACkgroundContext objectWithID:parentObjectID];
        // HIT THE WEBserviCE AND PUT THE RESULTS IN THE PARENT OBjeCT AND ITS CHILDREN,THEN SAVE...
[ManagedObjectContextHelper commit];

        dispatch_sync(dispatch_get_main_queue(),^{

            NsmanagedObjectContext *mainManagedObjectContext = [ManagedObjectContextHelper managedObjectContext];

            parent = (Parent*)[mainManagedObjectContext objectWithID:parentObjectID];
});
    });

错误中的conflictList似乎暗示它与父对象的ObjectID有关：

conflictList =     (
            "NSMergeConflict (0x856b130) for NsmanagedObject (0x93a60e0) with objectID '0xb07a6c0 <x-coredata://B7371EA1-2532-4D2B-8F3A-E09B56CC04F3/Child/p4>' 
with oldVersion = 21 and newVersion = 22 
and old object snapshot = {\n    parent = \"0xb192280 <x-coredata://B7371EA1-2532-4D2B-8F3A-E09B56CC04F3/Parent/p3>\";\n    name = \"New Child\";\n    returnedChildId = 337046373;\n    time = 38;\n} 
and new cached row = {\n    parent = \"0x856b000 <x-coredata://B7371EA1-2532-4D2B-8F3A-E09B56CC04F3/Parent/p3>\";\n    name = \"New Child\";\n    returnedChildId = 337046373;\n    time = 38;\n}"
        );

一旦我掌握了MOC,我就尝试放入refreshObject调用,理论上如果这是我们之前使用过的MOC(例如我们之前在主线程上使用了MOC而且很可能是这与助手类给我们的一样,然后在另一个线程中保存可能意味着我们需要显式刷新.但它没有任何区别,如果我长时间点击,它仍然会陷入僵局.

有没有人有任何想法？

编辑：如果我为所有例外设置了断点,则调试器会自动暂停if(！[moc save：& error])行,因此播放/暂停按钮已暂停并显示播放三角形.如果我禁用所有异常的断点,那么它实际记录冲突并继续 – 可能是因为合并策略当前设置为NSErrorMergePolicy – 所以我不认为它实际上是在线程上死锁.暂停时两个线程状态的@L_801_17@.