async DB operations

Question

My workflows are hosted in IIS. and each workflow inherits from asynccodeactivity. In BeginExecute, I call command.Beginxxx and in end execute i call EndExecutexxx. I'm using Database Access Block (DAAB).

protected override IAsyncResult BeginExecute(AsyncCodeActivityContext context, AsyncCallback callback, object state)
    {
        DbCommand command = null;
        DbConnection dbConnection = null;
        entlib.Database database;

        try
        {
            database = EnterpriseLibraryContainer.Current.GetInstance<entlib.Database>(DatabaseName.Get(context));
            dbConnection = database.CreateConnection();
            command = dbConnection.CreateCommand();
            command.CommandText = CommandText.Get(context);
            command.CommandType = CommandType.Get(context);

            //have removed few assignments here

            context.UserState = new AsyncDbState(database, command);
        }
        catch (Exception e)
        {
            if (command != null)
                command.Dispose();
            if (dbConnection != null)
                dbConnection.Dispose();

            throw e;
        }

        return (database.Beginxxx(command, callback, state));
    }


    protected override TResult EndExecute(AsyncCodeActivityContext context, IAsyncResult iResult)
    {
        TResult result = default(TResult);

        var userState = context.UserState as AsyncDbState;

            try
            {
                result = (TResult)userState.Database.Endxxx(iResult);
            }
            finally
            {
                if (null != userState && null != userState.Command)
                    userState.Command.Dispose();
            }

        return result;
    }

And sporadically it throws error in event log and terminates entire app pool. After Comments by @Will, I did trap inner exception and noticed the actual error happenes

in BeginExecute of a different activity, which inherits from asyncnativeactivity, I have

 var task = AsyncFactory<IDataReader>.Action(() => ExecuteMdxQuery(connectionStringSettings, mdxQuery, commandTimeout, cancellationToken), cancellationToken);                        

                    return AsyncFactory<IDataReader>.ToBegin(task, callback, state);

and AsyncFactory looks like this 

 public static Task<TResult> Action(Func<TResult> actionMethod,CancellationToken token)
    {
        TaskFactory factory = new TaskFactory();
        //TaskFactory factory = new TaskFactory(scheduler);
        return factory.StartNew<TResult>(() => actionMethod(), token);   
        }
  public static IAsyncResult ToBegin(Task<TResult> task, AsyncCallback callback, object state)
    {
        var tcs = new TaskCompletionSource<TResult>(state);
        var continuationTask = task.ContinueWith(t =>
        {
            if (task.IsFaulted)
            {
                tcs.TrySetException(task.Exception.InnerExceptions);
            }
            else if (task.IsCanceled)
            {
                tcs.TrySetCanceled();
            }
            else
            {
                tcs.TrySetResult(task.Result);
            }

An unhandled exception occurred and the process was terminated.

An unhandled exception occurred and the process was terminated.

Application ID: /LM/W3SVC/1/ROOT/workflowservice

Process ID: 7140

Exception: System.AggregateException

Message: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread.

StackTrace: at System.Threading.Tasks.TaskExceptionHolder.Finalize()

InnerException: Microsoft.AnalysisServices.AdomdClient.AdomdErrorResponseException

Message: Server: The current operation was cancelled because another operation in the transaction failed.

StackTrace: at Microsoft.AnalysisServices.AdomdClient.AdomdConnection.XmlaClientProvider.Microsoft.AnalysisServices.AdomdClient.IExecuteProvider.ExecuteTabular(CommandBehavior behavior, ICommandContentProvider contentProvider, AdomdPropertyCollection commandProperties, IDataParameterCollection parameters) at Microsoft.AnalysisServices.AdomdClient.AdomdCommand.ExecuteReader(CommandBehavior behavior) at WorkflowActivity.AsyncExecuteSafeReader.ExecuteMdxQuery(String connectionStringName, String mdxQuery, Nullable1 commandTimeout, CancellationToken cancellationToken) in d:\B\69\Sources\Infrastructure\WorkflowActivity\AsyncExecuteSafeReader.cs:line 222 at AsyncExecuteSafeReader.ExecuteMdxQuery(String connectionStringName, String mdxQuery, Nullable1 commandTimeout, CancellationToken cancellationToken) in d:\B\69\Sources\Infrastructure\WorkflowActivity\AsyncExecuteSafeReader.cs:line 239 at WorkflowActivity.AsyncExecuteSafeReader.<>c__DisplayClassd.b__a() in d:\B\69\Sources\Infrastructure\WorkflowActivity\AsyncExecuteSafeReader.cs:line 180 at System.Threading.Tasks.Task`1.InvokeFuture(Object futureAsObj) at System.Threading.Tasks.Task.Execute()

Answer 1

@Will, Looks like Mars = false in connection string has resolved it. haven't been able to replicate it. theory is - a query returned result. and end execute was called. but it also returned another resultset? which is why call back was being invoked. but end execute was already called by then. But then again, it's sporadic. If this theory is true, my understanding is that it could have failed all the time. So far haven't been able to crash at all. there were also few procedures which had rowcount on. I'm grateful you took time to comment and share your theory on this. learnt a lot.