Cocoa 带核心数据的中断多线程

这是先前一个问题的一个更好的聚焦版本，该问题涉及一个与以前完全不同的主题

我正在开发一个具有多线程的Cocoa核心数据应用程序。有一首歌和一位艺术家；每首歌都有艺术家的关系。此处未引用代表代码文件；它或多或少看起来像是XCode生成的模板

我使用前一种技术比使用后一种技术要好得多，而且任何多线程功能都来自核心数据模板。当我用一种方法完成所有ManagedObjectContext工作时，我很好。当我将fetch或insert然后return对象工作放入一个单独的方法中时，应用程序会在新方法的return语句处停止（但不会崩溃），如下所示。新的方法甚至有自己的MOC是安全的，而且没有任何帮助。结果是歌曲中添加了一个元素，并在生成艺术家后停止

我没有错误或异常，我也不知道为什么。我已经调试好了wazoo。我的理论是，发生的任何错误都在另一个线程中，而我正在观看的线程永远都在等待某些东西

getArtistObject:有什么问题，如何修复？谢谢

- (void)main
{
    NSInteger songCount = 1;
    NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init];
    [moc setPersistentStoreCoordinator:[[self delegate] persistentStoreCoordinator]];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextDidSave:) name:NSManagedObjectContextDidSaveNotification object:moc];

/* songDict generated here */

    for (id key in songDict)
    {
        NSManagedObject *song = [NSEntityDescription insertNewObjectForEntityForName:@"Song" inManagedObjectContext:moc];
        [song setValue:[songDictItem objectForKey:@"Name"] forKey:@"title"];
        [song setValue:[self getArtistObject:(NSString *) [songDictItem objectForKey:@"Artist"]] forKey:@"artist"];

        [songDictItem release];

        songCount++;
    }

    NSError *error;
    if (![moc save:&error])
    [NSApp presentError:error];

    [[NSNotificationCenter defaultCenter] removeObserver:self name:NSManagedObjectContextDidSaveNotification object:moc];
    [moc release], moc = nil;
    [[self delegate] importDone];
}

- (NSManagedObject*) getArtistObject:(NSString*)theArtist
{
    NSError *error = nil;
    NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init];
    [moc setPersistentStoreCoordinator:[[self delegate] persistentStoreCoordinator]];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextDidSave:) name:NSManagedObjectContextDidSaveNotification object:moc];

    NSFetchRequest *fetch = [[[NSFetchRequest alloc] init] autorelease];
    NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Artist" inManagedObjectContext:moc];
    [fetch setEntity:entityDescription];

    // object to be returned
    NSManagedObject *artistObject = [[NSManagedObject alloc] initWithEntity:entityDescription insertIntoManagedObjectContext:moc];

    // set predicate (artist name)
    NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"name = \"%@\"", theArtist]];
    [fetch setPredicate:pred];

    NSArray *response = [moc executeFetchRequest:fetch error:&error];

    if (error)
    [NSApp presentError:error];

    if ([response count] == 0) // empty resultset --> no artists with this name
    {
    [artistObject setValue:theArtist forKey:@"name"];
    NSLog(@"%@ not found. Adding.", theArtist);

    return artistObject;
    }
    else
    return [response objectAtIndex:0];
}

@end

---

尝试在访问托管对象上下文之前锁定它，并在使用完毕后再次解锁它：

- (void)main
{
    NSInteger songCount = 1;
    NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init];
    [moc lock];
    [moc setPersistentStoreCoordinator:[[self delegate] persistentStoreCoordinator]];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextDidSave:) name:NSManagedObjectContextDidSaveNotification object:moc];
     [moc unlock];

/* songDict generated here */

    for (id key in songDict)
    {
        [moc lock];
        NSManagedObject *song = [NSEntityDescription insertNewObjectForEntityForName:@"Song" inManagedObjectContext:moc];
        [moc unlock];
        [song setValue:[songDictItem objectForKey:@"Name"] forKey:@"title"];
        [song setValue:[self getArtistObject:(NSString *) [songDictItem objectForKey:@"Artist"]] forKey:@"artist"];

        [songDictItem release];

        songCount++;
    }

    NSError *error;
    [moc lock];
    if (![moc save:&error])
    [NSApp presentError:error];
    [moc unlock];

    [moc lock];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:NSManagedObjectContextDidSaveNotification object:moc];
    [moc unlock];
    [moc release], moc = nil;
    [[self delegate] importDone];
}

- (NSManagedObject*) getArtistObject:(NSString*)theArtist
{
    NSError *error = nil;
    NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init];
    [moc lock];
    [moc setPersistentStoreCoordinator:[[self delegate] persistentStoreCoordinator]];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextDidSave:) name:NSManagedObjectContextDidSaveNotification object:moc];
    [moc unlock];

    NSFetchRequest *fetch = [[[NSFetchRequest alloc] init] autorelease];
    [moc lock];
    NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Artist" inManagedObjectContext:moc];
    [moc unlock];
    [fetch setEntity:entityDescription];

    // object to be returned
    [moc lock];
    NSManagedObject *artistObject = [[NSManagedObject alloc] initWithEntity:entityDescription insertIntoManagedObjectContext:moc];
    [moc unlock];

    // set predicate (artist name)
    NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"name = \"%@\"", theArtist]];
    [fetch setPredicate:pred];

    [moc lock];
    NSArray *response = [moc executeFetchRequest:fetch error:&error];
    [moc unlock];

    if (error)
    [NSApp presentError:error];

    if ([response count] == 0) // empty resultset --> no artists with this name
    {
    [artistObject setValue:theArtist forKey:@"name"];
    NSLog(@"%@ not found. Adding.", theArtist);

    return artistObject;
    }
    else
    return [response objectAtIndex:0];
}

@end

---

尝试在访问托管对象上下文之前锁定它，并在使用完毕后再次解锁它：

- (void)main
{
    NSInteger songCount = 1;
    NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init];
    [moc lock];
    [moc setPersistentStoreCoordinator:[[self delegate] persistentStoreCoordinator]];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextDidSave:) name:NSManagedObjectContextDidSaveNotification object:moc];
     [moc unlock];

/* songDict generated here */

    for (id key in songDict)
    {
        [moc lock];
        NSManagedObject *song = [NSEntityDescription insertNewObjectForEntityForName:@"Song" inManagedObjectContext:moc];
        [moc unlock];
        [song setValue:[songDictItem objectForKey:@"Name"] forKey:@"title"];
        [song setValue:[self getArtistObject:(NSString *) [songDictItem objectForKey:@"Artist"]] forKey:@"artist"];

        [songDictItem release];

        songCount++;
    }

    NSError *error;
    [moc lock];
    if (![moc save:&error])
    [NSApp presentError:error];
    [moc unlock];

    [moc lock];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:NSManagedObjectContextDidSaveNotification object:moc];
    [moc unlock];
    [moc release], moc = nil;
    [[self delegate] importDone];
}

- (NSManagedObject*) getArtistObject:(NSString*)theArtist
{
    NSError *error = nil;
    NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init];
    [moc lock];
    [moc setPersistentStoreCoordinator:[[self delegate] persistentStoreCoordinator]];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextDidSave:) name:NSManagedObjectContextDidSaveNotification object:moc];
    [moc unlock];

    NSFetchRequest *fetch = [[[NSFetchRequest alloc] init] autorelease];
    [moc lock];
    NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Artist" inManagedObjectContext:moc];
    [moc unlock];
    [fetch setEntity:entityDescription];

    // object to be returned
    [moc lock];
    NSManagedObject *artistObject = [[NSManagedObject alloc] initWithEntity:entityDescription insertIntoManagedObjectContext:moc];
    [moc unlock];

    // set predicate (artist name)
    NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"name = \"%@\"", theArtist]];
    [fetch setPredicate:pred];

    [moc lock];
    NSArray *response = [moc executeFetchRequest:fetch error:&error];
    [moc unlock];

    if (error)
    [NSApp presentError:error];

    if ([response count] == 0) // empty resultset --> no artists with this name
    {
    [artistObject setValue:theArtist forKey:@"name"];
    NSLog(@"%@ not found. Adding.", theArtist);

    return artistObject;
    }
    else
    return [response objectAtIndex:0];
}

@end

---

您不能锁定NSManagedObjects

您无法锁定NSManagedObjects

不行。它仍然点击“返回artistObject；”然后停下来。有趣的是，如果我多次单击触发此操作的按钮，它每次都会对第一首歌曲/艺术家重复相同的操作。有没有一种方法可以使用调试器来找出它在等待什么（如果有的话）？我不知道，但希望其他人可以加入。没有。它仍然点击“返回artistObject；”然后停下来。有趣的是，如果我多次单击触发此操作的按钮，它每次都会对第一首歌曲/艺术家重复相同的操作。有没有一种方法可以使用调试器来找出它在等待什么（如果有的话）？我不知道，但希望其他人可以加入。