Thread safe variable in VB.NET

Question

Is this the right way of declaration dbreaders when mulitple users access the same page?

public dbReader as system.Data.IDataReader at class level or

Dim dbReader as System.Data.IDataReader in each function inside a class.

What would be the best practice to make the dbReader thread safe in VB.Net?

Does declaring them as static makes it thread safe?

Thanks in Advance,

Answer 1

I would recommend you using reentrant functions when possible which are thread safe by definition instead of using class fields:

Function GetIds() As IEnumerable(Of Integer)
    Dim result = New List(Of Integer)()
    Using conn = New SqlConnection("SomeConnectionString")
        Using cmd = conn.CreateCommand()
            conn.Open()
            cmd.CommandText = "SELECT id FROM foo"
            Using reader = cmd.ExecuteReader()
                While reader.Read()
                    result.Add(reader.GetInt32(0))
                End While
            End Using
        End Using
    End Using
    Return result
End Function

Answer 2

If you are Diming the variable in a function, no other thread can access that variable making it thread-safe by definition.

However, if you are declaring it at a class level, you might want to use SyncLock which will prevent other threads from accessing it if it is currently being used by an other one.

Example:

Public Sub AccessVariable()
    SyncLock Me.dbReader
         'Work With dbReader
    End SyncLock
End Sub