Monotouch数据同步-为什么我的代码有时会导致sqlite错误?

我有以下几个调用(实际上比这个多一些—这里讨论的是整个方法):

ThreadPool.QueueUserWorkItem(Database.Instance.RefreshEventData);
ThreadPool.QueueUserWorkItem(Database.Instance.RefreshLocationData);
ThreadPool.QueueUserWorkItem(Database.Instance.RefreshActData);

上面调用的一个刷新方法的示例是(它们都遵循相同的模式,只需调用不同的服务并填充不同的表):

public void RefreshEventData (object state)
        {
            Console.WriteLine ("in RefreshEventData");
            var eservices = new AppServicesClient (new BasicHttpBinding (), new EndpointAddress (this.ServciceUrl));

            //default the delta to an old date so that if this is first run we get everything
            var eventsLastUpdated = DateTime.Now.AddDays (-100);

            try {
                eventsLastUpdated = (from s in GuideStar.Data.Database.Main.Table<GuideStar.Data.Event> ()
                    orderby s.DateUpdated descending
                    select s).ToList ().FirstOrDefault ().DateUpdated;

            } catch (Exception ex1) {
                Console.WriteLine (ex1.Message);
            }

            try {
                eservices.GetAuthorisedEventsWithExtendedDataAsync (this.User.Id, this.User.Password, eventsLastUpdated);
            } catch (Exception ex) {
                Console.WriteLine ("error updating events: " + ex.Message);
            }

            eservices.GetAuthorisedEventsWithExtendedDataCompleted += delegate(object sender, GetAuthorisedEventsWithExtendedDataCompletedEventArgs e) {

                try {

                    List<Event> newEvents = e.Result.ToList ();

                    GuideStar.Data.Database.Main.EventsAdded = e.Result.Count ();

                    lock (GuideStar.Data.Database.Main) {
                        GuideStar.Data.Database.Main.Execute ("BEGIN");

                        foreach (var s in newEvents) {

                            GuideStar.Data.Database.Main.InsertOrUpdateEvent (new GuideStar.Data.Event { 
                                Name = s.Name, 
                                DateAdded = s.DateAdded, 
                                DateUpdated = s.DateUpdated, 
                                Deleted = s.Deleted, 
                                StartDate = s.StartDate,
                                Id = s.Id, 
                                Lat = s.Lat, 
                                Long = s.Long   
                            });

                        }

                        GuideStar.Data.Database.Main.Execute ("COMMIT");
                        LocationsCount = 0;
                    }
                } catch (Exception ex) {
                    Console.WriteLine("error InsertOrUpdateEvent " + ex.Message);
                } finally {
                    OnDatabaseUpdateStepCompleted (EventArgs.Empty);
                }

            };
        }

第一次就可以了,但有时不适用于: http://monobin.com/__m6c83107d

我想第一个问题是-这一切都好吗?我不习惯使用线程和锁,所以我徘徊在新的领域为我。像这样使用QueueUserWorkItem可以吗?在执行批量插入/更新之前,我是否应该使用lock?例如:

public void InsertOrUpdateEvent(Event festival){

            try {
                if (!festival.Deleted) {
                    Main.Insert(festival, "OR REPLACE");
                }else{
                    Main.Delete<Event>(festival);
                }
            } catch (Exception ex) {
                Console.WriteLine("InsertOrUpdateEvent failed: " + ex.Message);
            }

        }

接下来的问题是-我做错了什么导致了这些sqlite问题?