System.ObjectDisposedException：无法访问已处置的对象，ASP.NET Core 3.1

Question

我正在 ASP.NET Core 3.1 中使用 SignalR 编写 API。我是 .NET Core 的新手，也是 SignalR 的新手。我在执行交易中运行的 MongoDB (Atlas) 查询时遇到问题。看起来事务会话在查询执行之前就已经过期了。我很确定这是一个 async/await 问题，但似乎无法修复它。

我的 Hub 方法如下所示：

public async Task<bool> UpdateProfile(object profileDto)
{
  try
  {
    ProfileDTO profile = ((JsonElement) profileDto).ToObject<ProfileDTO>();
    _profile.UpdateProfile(profile);
    return true;
  }
  catch
  {
    return false;
  }
}

_profile.UpdateProfile() 方法如下所示：

public void UpdateProfile(ProfileDTO profileDto)
{
  _databaseService.ExecuteInTransaction(async session =>
  {
    var profile = _mapper.Map<ProfileModel>(profileDto);
    var existingUser = (await _userCollectionService
        .FindAsync(session, user => user.Profille.Sub == profileDto.sub)
      ).FirstOrDefault();

    if (existingUser == null)
    {
      var newUser = new UserModel();
      newUser.Profille = profile;
      await _userCollectionService.CreateAsync(session, newUser);
    }
    else
    {
      existingUser.Profille = profile;
      // the error occurs on the following line
      await _userCollectionService.UpdateAsync(session, existingUser.Id, existingUser);
    }
  });
}

我的 ExecuteInTransaction() 方法是对 transaction/session 过程的概括尝试，看起来像这样：

public async void ExecuteInTransaction(DatabaseAction databaseAction)
{
  using (var session = await Client.StartSessionAsync())
  {
    try
    {
      session.StartTransaction();
      databaseAction(session);
      await session.CommitTransactionAsync();
    }
    catch (Exception e)
    {
      await session.AbortTransactionAsync();
      throw e;
    }
  }
}

我已经指出了 UpdateProfile() 中发生错误的行。完整的错误如下所示：

System.ObjectDisposedException: Cannot access a disposed object. Object name: 'MongoDB.Driver.Core.Bindings.CoreSessionHandle'. at MongoDB.Driver.Core.Bindings.WrappingCoreSession.ThrowIfDisposed() at MongoDB.Driver.Core.Bindings.WrappingCoreSession.get_IsInTransaction() at MongoDB.Driver.ClientSessionHandle.get_IsInTransaction() at MongoDB.Driver.MongoCollectionImpl1.CreateBulkWriteOperation(IClientSessionHandle session, IEnumerable1 requests, BulkWriteOptions options) at MongoDB.Driver.MongoCollectionImpl1.BulkWriteAsync(IClientSessionHandle session, IEnumerable1 requests, BulkWriteOptions options, CancellationToken cancellationToken) at MongoDB.Driver.MongoCollectionBase1.ReplaceOneAsync(FilterDefinition1 filter, TDocument replacement, ReplaceOptions options, Func3 bulkWriteAsync) at IndistinctChatter.API.Services.Business.Profile.<>c__DisplayClass5_0.<<UpdateProfile>b__0>d.MoveNext() in /Volumes/Data/Users/marknorgate/Documents/Development/source/indistinct-chatter/api-dotnet/Services/Business/Profile.cs:line 48 --- End of stack trace from previous location where exception was thrown --- at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__139_1(Object state) at System.Threading.QueueUserWorkItemCallback.<>c.<.cctor>b__6_0(QueueUserWorkItemCallback quwi) at System.Threading.ExecutionContext.RunForThreadPoolUnsafe[TState](ExecutionContext executionContext, Action1 callback, TState& state) at System.Threading.QueueUserWorkItemCallback.Execute() at System.Threading.ThreadPoolWorkQueue.Dispatch() at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()

所以 session 对象似乎在 await _userCollectionService.UpdateAsync(session, existingUser.Id, existingUser); 行执行之前就过期了。 await session.CommitTransactionAsync(); 行首先执行。

我哪里错了？我觉得 Task 即将到来...

Answer 1

好的，我找到了解决方法，尽管我对解决方案并不完全满意。

我发现了 AutoResetEvent()，因此修改了我的代码：

public async void ExecuteInTransaction(DatabaseAction databaseAction)
{
  AutoResetEvent autoResetEvent = new AutoResetEvent(false);

  using var session = await Client.StartSessionAsync();

  try
  {
    session.StartTransaction();
    databaseAction(session, autoResetEvent);
    autoResetEvent.WaitOne();
    await session.CommitTransactionAsync();
  }
  catch (Exception e)
  {
    await session.AbortTransactionAsync();
    throw e;
  }
}

和

public void UpdateProfile(ProfileDTO profileDto)
{
  _databaseService.ExecuteInTransaction(async (session, autoResetEvent) =>
  {
    var profile = _mapper.Map<ProfileModel>(profileDto);
    var existingUser = (await _userCollectionService
        .FindAsync(session, user => user.Profille.Sub == profileDto.sub)
      ).FirstOrDefault();

    if (existingUser == null)
    {
      var newUser = new UserModel();
      newUser.Profille = profile;
      await _userCollectionService.CreateAsync(session, newUser);
    }
    else
    {
      existingUser.Profille = profile;
      await _userCollectionService.UpdateAsync(session, existingUser.Id, existingUser);
    }

    autoResetEvent.Set();
  });
}

似乎可行，但这是我需要记住的每个数据库操作结束时的额外步骤。如果有人可以对此进行改进，我将很高兴听到！

Answer 2

您的 DatabaseAction 不是异步委托。好像是Action<T>，其实你真正需要的是Func<T, Task>。因此，当您执行 async session => 时，该代码会变成 async void 签名。由于它是 void，您不能 await。这会导致您的 async 代码被调度到线程池线程并立即调用 returns。这具有 await session.CommitTransactionAsync() 提交的连锁反应，而您的代表可能还没有开始运行。 ExecuteInTransaction 中的代码现在被认为是“完成”并退出，由于 using 阻塞，您的 session 沿途处理。

要解决此问题，您需要更改 DatabaseAction 的签名，然后 await databaseAction(session);

System.ObjectDisposedException：无法访问已处置的对象，ASP.NET Core 3.1

System.ObjectDisposedException: Cannot access a disposed object, ASP.NET Core 3.1

c#

asp.net

mongodb

async-await

signalr