Filling Datasets from Oracle within VB Threads

I'm trying to run a couple of PL/SQL procedures from within a VB app. The procedures take a while to run so I intend to put them into separate threads (the subject of which I am new to)

Currently, each thread calls a function, which in turn calls the following code:

' Function getDataSet
' builds a data set from given information
' Parameters:
'   aCommand - the PL/SQL procedure to call
'   aParamCollection - an oraParameterCollection object containing all the parameters
'   aDataSet - a data set to hold the results
' Returns:
'   number of rows retrieved

Public Function getDataSet( _
    ByVal aCommand As String, _
    ByVal aParamCollection As oraParameterCollection, _
    ByRef aDataSet As DataSet _
    ) As Integer

    Dim result As Integer = 0

    ' define commands etc
    Dim cmd As OracleCommand = New OracleCommand(aCommand, dbConn)
    cmd.CommandType = CommandType.StoredProcedure

    ' add parameters for the query
    For i As Integer = 0 To aParamCollection.getParameterCount() - 1
        cmd.Parameters.Add(New OracleParameter( _
                                aParamCollection.getParameterByIndex(i).ParameterName, _
                                aParamCollection.getParameterByIndex(i).ParameterType)).Value = _
                                aParamCollection.getParameterByIndex(i).ParameterValue
    Next

    Dim param As OracleParameter = New OracleParameter("io_cursor", OracleDbType.RefCursor)
    cmd.Parameters.Add(param).Direction = ParameterDirection.Output
    CheckConnection()
    cmd.ExecuteNonQuery()

    Dim cur As OracleRefCursor
    cur = param.Value
    cmd.Dispose()

    Dim theAdaptr As New OracleDataAdapter

    If aDataSet IsNot Nothing Then
        theAdaptr.Fill(aDataSet, cur)
        result = aDataSet.T开发者_开发问答ables(0).Rows.Count
    End If

    Return result

End Function

Where:

aCommand = the PL/SQL proc to execute

aParamCollection = a custom class that holds parameters, types and values

aDataSet = the data set to hold the resulting data

However, when I run the app, I get an access violation at this point:

theAdaptr.Fill(aDataSet, cur)

I assume that the separate threads can't make the call to Fill at the same time, is this correct? I am currently kicking off each thread as so:

    Dim th_Mean As New Thread(AddressOf getMeanData)
    Dim th_Stdev As New Thread(AddressOf getStdevData)

    th_Mean.Name = "th_Mean"
    th_Stdev.Name = "th_Stdev"

    th_Mean.Start()
    th_Stdev.Start()    

    Do While th_Mean.IsAlive Or th_Stdev.IsAlive
    Loop

Ultimately, my question is, what should I be doing so as to avoid the access violation happening?

Thanks for reading BBz

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Have you considered adding the parallelism in the database? Parallelism is (relatively) easy with declarative SQL. Depending on your stored procedures, it may be as simple as finding the slow query and adding a hint, something like:

select /*+ parallel(my_table) */ * from my_table;

If the procedure is more about row-by-row processing than queries you may need to look into parallel pipelined functions.