Question

首先，我已经在很多NullReferenceException问题中搜索了SO。 here和here

我收到错误＆＃34;对象引用没有设置为对象的实例＆＃34;当我尝试拨打Task.WaitAll(tasks);

时

我确信在尝试调用方法之前，我正在初始化所有对象。下面是代码snipet：

public IList<ResourceFreeBusyDto> GetResourceFreeBusy(int requesterId, int[] resourceIds, DateTime start, DateTime end)
    {
        IList<ResourceFreeBusyDto> result = new List<ResourceFreeBusyDto>();

        ValidateFreeBusyInputs(resourceIds, start, end);

        List<Task<IList<ResourceFreeBusyDto>>> tasks = new List<Task<IList<ResourceFreeBusyDto>>>();
        TimeSpan timeout = new TimeSpan(0,0,30); // 30 seconds          

        // Split resources to persons and meetingRooms
        List<int> personIds;
        List<int> meetingRoomIds;

        SplitResourceIds(resourceIds, out personIds, out meetingRoomIds);

        // Go online for persons
        if (personIds.Count > 0)
        {
            //result.AddRange(GetResourceFreeBusyOnline(requesterId, personIds.ToArray(), start, end)); // paralelizovat
            Task<IList<ResourceFreeBusyDto>> task = Task.Factory.StartNew(() => GetResourceFreeBusyOnline(requesterId, personIds.ToArray(), start, end));
            tasks.Add(task);
        }

        // Go online for meetingrooms if they are not cached in DB
        if (meetingRoomIds.Count > 0)
        {
            DateTime? lastModifiedMeetingRoomFreeBusy = new DateTime();

            lastModifiedMeetingRoomFreeBusy = freeBusyRepository.GetMinTimeStamp();

            if (lastModifiedMeetingRoomFreeBusy.Value.AddMinutes(1) < DateTime.UtcNow || lastModifiedMeetingRoomFreeBusy == null)
            {
                //result.AddRange(GetResourceFreeBusyOnline(requesterId, meetingRoomIds.ToArray(), start, end)); // mrIDs
                Task<IList<ResourceFreeBusyDto>> task = Task.Factory.StartNew(() => GetResourceFreeBusyOnline(requesterId, resourceIds, start, end));
                tasks.Add(task);
            }
            else
            {
                //result.AddRange(GetMeetingRoomsFreeBusyCached(requesterId, meetingRoomIds.ToArray(), start, end)); // mrIDs
                Task<IList<ResourceFreeBusyDto>> task = Task.Factory.StartNew(() => GetMeetingRoomsFreeBusyCached(requesterId, resourceIds, start, end));
                tasks.Add(task);
            }
        }

        bool status = false;

        try
        {
            var a = tasks.ToArray();
            Task.WaitAll(a);
            status = Task.WaitAll(tasks.ToArray(), timeout);
        }
        catch (Exception ex)
        {

            Log.Fatal(ex);
        }


        if (status == false)
        {
            throw new ApplicationException(
            string.Format("Timeout expired." +
            " The timeout period elapsed prior to completion of the asynchronous importing task executing" +
            " or the server is not responding. Try it later!"));
        }
        else
        {
            foreach (Task<IList<ResourceFreeBusyDto>> task in tasks)
            {
                result.AddRange(task.Result);
            }
        }

        return result;

    }

注意

var a = tasks.ToArray();
Task.WaitAll(a);

是抛出异常的测试。 var a = tasks.ToArray();正在传递而没有错误。

此处抛出异常：

Task.WaitAll(a);

在这里

status = Task.WaitAll(tasks.ToArray(), timeout);

你能告诉我发生了什么吗？我可以在调试期间看到tasks已初始化。

P.S。注释行例如：result.AddRange(GetResourceFreeBusyOnline(requesterId, meetingRoomIds.ToArray(), start, end));是在单个线程中调用方法的行，它在没有错误的情况下传递并返回预期结果。

堆栈

2016-12-22 13:24:18,844 [9] FATAL Tieto.MyMeetings.Tasks.FreeBusy.FreeBusyTasks - System.AggregateException: One or more errors occurred. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at SharpArch.NHibernate.Web.Mvc.WebSessionStorage.GetSimpleSessionStorage()
   at SharpArch.NHibernate.Web.Mvc.WebSessionStorage.GetSessionForKey(String factoryKey)
   at SharpArch.NHibernate.NHibernateSession.CurrentFor(String factoryKey)
   at SharpArch.NHibernate.NHibernateRepositoryWithTypedId`2.get_Session()
   at SharpArch.NHibernate.LinqRepositoryWithTypedId`2.FindAll()
   at Tieto.MyMeetings.Tasks.FreeBusy.FreeBusyTasks.GetResourceFreeBusyOnline(Int32 requesterId, Int32[] resourceIds, DateTime start, DateTime end) in C:\_Hg\Tieto.MyMeetings\source\server\Tieto.MyMeetings.Tasks\FreeBusy\FreeBusyTasks.cs:line 238
   at Tieto.MyMeetings.Tasks.FreeBusy.FreeBusyTasks.<>c__DisplayClass7_0.<GetResourceFreeBusy>b__0() in C:\_Hg\Tieto.MyMeetings\source\server\Tieto.MyMeetings.Tasks\FreeBusy\FreeBusyTasks.cs:line 83
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.Task.WaitAll(Task[] tasks, Int32 millisecondsTimeout, CancellationToken cancellationToken)
   at System.Threading.Tasks.Task.WaitAll(Task[] tasks, Int32 millisecondsTimeout)
   at System.Threading.Tasks.Task.WaitAll(Task[] tasks)
   at Tieto.MyMeetings.Tasks.FreeBusy.FreeBusyTasks.GetResourceFreeBusy(Int32 requesterId, Int32[] resourceIds, DateTime start, DateTime end) in C:\_Hg\Tieto.MyMeetings\source\server\Tieto.MyMeetings.Tasks\FreeBusy\FreeBusyTasks.cs:line 113
---> (Inner Exception #0) System.NullReferenceException: Object reference not set to an instance of an object.
   at SharpArch.NHibernate.Web.Mvc.WebSessionStorage.GetSimpleSessionStorage()
   at SharpArch.NHibernate.Web.Mvc.WebSessionStorage.GetSessionForKey(String factoryKey)
   at SharpArch.NHibernate.NHibernateSession.CurrentFor(String factoryKey)
   at SharpArch.NHibernate.NHibernateRepositoryWithTypedId`2.get_Session()
   at SharpArch.NHibernate.LinqRepositoryWithTypedId`2.FindAll()
   at Tieto.MyMeetings.Tasks.FreeBusy.FreeBusyTasks.GetResourceFreeBusyOnline(Int32 requesterId, Int32[] resourceIds, DateTime start, DateTime end) in C:\_Hg\Tieto.MyMeetings\source\server\Tieto.MyMeetings.Tasks\FreeBusy\FreeBusyTasks.cs:line 238
   at Tieto.MyMeetings.Tasks.FreeBusy.FreeBusyTasks.<>c__DisplayClass7_0.<GetResourceFreeBusy>b__0() in C:\_Hg\Tieto.MyMeetings\source\server\Tieto.MyMeetings.Tasks\FreeBusy\FreeBusyTasks.cs:line 83
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()<---

---> (Inner Exception #1) System.NullReferenceException: Object reference not set to an instance of an object.
   at SharpArch.NHibernate.Web.Mvc.WebSessionStorage.GetSimpleSessionStorage()
   at SharpArch.NHibernate.Web.Mvc.WebSessionStorage.GetSessionForKey(String factoryKey)
   at SharpArch.NHibernate.NHibernateSession.CurrentFor(String factoryKey)
   at SharpArch.NHibernate.NHibernateRepositoryWithTypedId`2.get_Session()
   at SharpArch.NHibernate.LinqRepositoryWithTypedId`2.FindAll(ILinqSpecification`1 specification)
   at Tieto.MyMeetings.Tasks.FreeBusy.FreeBusyTasks.GetMeetingRoomsFreeBusyCached(Int32 requesterId, Int32[] meetingRoomIds, DateTime start, DateTime end) in C:\_Hg\Tieto.MyMeetings\source\server\Tieto.MyMeetings.Tasks\FreeBusy\FreeBusyTasks.cs:line 196
   at Tieto.MyMeetings.Tasks.FreeBusy.FreeBusyTasks.<>c__DisplayClass7_0.<GetResourceFreeBusy>b__2() in C:\_Hg\Tieto.MyMeetings\source\server\Tieto.MyMeetings.Tasks\FreeBusy\FreeBusyTasks.cs:line 103
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()<---

Answer 1

Task.WaitAll不会抛出此异常。它将重新抛出其任务之一引发的异常。没有完整的异常和调用堆栈（由EnumSet.noneOf()返回），这是不可能确定的，但标准指南也适用于此 - 某处，某种程度上，使用了未初始化的变量或参数。

例如：

Exception.ToString()

可能会将List<int> personIds; List<int> meetingRoomIds; SplitResourceIds(resourceIds, out personIds, out meetingRoomIds);和personIds都设置为null。这意味着

meetingRoomIds

会在任务中抛出异常，在调用var task = Task.Factory.StartNew(() => GetResourceFreeBusyOnline(requesterId, personIds.ToArray(), start, end));时会重新引发异常。

要解决此问题，请按照重复问题中的建议进行操作。检查参数是否为null，调试代码，检查异常的完整调用堆栈。 Task.WaitAll将抛出AggregateException，其中包含InnerExceptions属性中的所有基础异常。

至少你应该抓住Task.WaitAll来分别处理和记录任务中引发的异常。

最后，使用AggregateException，async/await和Task.Run代替StartNew和Task.WaitAll。 await Task.WhenAll打开await并引发基础异常，这使调试变得更加容易。

<强>更新

在调用堆栈中，AggregateException调用Tieto.MyMeetings.Tasks.FreeBusy.FreeBusyTasks.GetMeetingRoomsFreeBusyCached并传递null参数或包含null的项列表。这些值可能用于创建会话密钥，因为在抛出异常之前会调用SharpArch.NHibernate.LinqRepositoryWithTypedId'2.FindAll。

找到确切的问题需要调试代码并进入SharpArch.NHibernate.Web.Mvc.WebSessionStorage.GetSessionForKey

使用任务获取＆＃34;对象引用未设置为对象的实例＆＃34;

1 个答案: