如何防止在错误线程上访问领域

我试图在串行队列上执行所有操作。

我已声明队列属性:

@property (nonatomic, strong) dispatch_queue_t realmQueue;
@property (strong,nonatomic) RLMRealm *secureRealm;

我使用singleton初始化队列:

+ (id)sharedInstance {
    static ActivityManager *sharedManager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedManager = [[self alloc] init];

    });

    return sharedManager;
}

-(id)init{
    self.realmQueue = dispatch_queue_create("realm_activity", DISPATCH_QUEUE_SERIAL);
    dispatch_async(self.realmQueue, ^{
    _secureRealm = [RLMRealm defaultRealm];
    });
    return self;
}

-(NSArray *)getDataOnSettingFilter{

    NSMutableArray *activityArr = [NSMutableArray array];
    NSString *filterSQL = //;

    RLMResults *activityResults = [[[self getActivitySource]activities] objectsWhere:filterSQL];

    dispatch_async(self.realmQueue, ^{
        [_secureRealm beginWriteTransaction];

        for (RealmActivity *activity in activityResults){

        //modify realm properties

        [_secureRealm addOrUpdateObject:activity];
        [activityArr addObject:activity];
    }
        [_secureRealm commitWriteTransaction];
    });
    return [activityArr copy];
}

当我使用调用上述方法时:

  [[ActivityManager sharedInstance]getDataOnSettingFilter]

我做错了什么。如何检查我是否总是在正确的线程上调用领域?