Question

Using C#, I am noticing a significant difference in perfomance when populating a list with instances of a dynamically generated type versus a simple struct. The code below includes 4 different methods for populating a list with 100,000 objects.

Each method performs differently:

Button1: 15 milliseconds

Button2: 31 milliseconds

Button3 & 4: 300 milliseconds

Note, the code for button 3 & 4 came from this topic

Could anyone explain why the dynamically created object is slower?

    public struct DataRow
    {
        public double t;
        public double vf;
        public double im;

        public double T { get { return t; } set { t = value; } }
        public double Vf { get { return vf; } set { vf = value; } }
        public double Im { get { return im; } set { im = value; } }
    }

    //Use struct defined above
    private void button1_Click(object sender, EventArgs e)
    {
        int n = 0;

        //adding rows
        List<DataRow> myTable = new List<DataRow>();
        DataRow myRow = new DataRow();

        start = DateTime.Now;

        while (n < 100000)
        {
            myRow.T = n * 1.0;
            myRow.Vf = 2.0;
            myRow.Im = 4.0;

            myTable.Add(myRow);

            n++;
        }
        end = DateTime.Now;
        System.TimeSpan diff = end.Subtract(start);
        label2.Text = diff.Seconds.ToString();
        label4.Text = diff.Milliseconds.ToString();

        dataGridView1.DataSource = myTable;
    }

    //define the list as it is done on buttons 3 & 4 but use the static struct
    private void button2_Click(object sender, EventArgs e)
    {
        Type myType = typeof(DataRow);

        Type listType = typeof(List<>);

        Type myListType = listType.MakeGenericType(myType);

        IList myTable = (IList)Activator.CreateInstance(myListType);

        DataRow bRow = new DataRow();

        int n = 0;
        start = DateTime.Now;
        while (n < 100000)
        {
            bRow.t = n * 1.0;
            bRow.vf = 2.0;
            bRow.im = 4.0;
            myTable.Add(bRow);

            n++;
        }
        end = DateTime.Now;
        System.TimeSpan diff = end.Subtract(start);
        label2.Text = diff.Seconds.ToString();
        label4.Text = diff.Milliseconds.ToString();
        dataGridView1.DataSource = myTable;

    }

    //Create assy at runtime and load dll
    private void button3_Click(object sender, EventArgs e)
    {
        Type myType = CreateDynRow();
        Assembly myAssy = Assembly.LoadFrom("DynaRowAssy.dll");
        Type myRow = myAssy.GetType("DynaRow");

        Type listType = typeof(List<>);

        Type myListType = listType.MakeGenericType(myRow);

        IList myTable = (IList)Activator.CreateInstance(myListType);

        FieldInfo piT = myRow.GetField("t");
        FieldInfo piVf = myRow.GetField("vf");
        FieldInfo piIm = myRow.GetField("im");

        ValueType aRow = (ValueType)Activator.CreateInstance(myRow);

        int n = 0;
        start = DateTime.Now;
        while (n < 100000)
        {
            piT.SetValue(aRow, 1 * n);
            piVf.SetValue(aRow, 2.0);
            piIm.SetValue(aRow, 4.0);
            myTable.Add(aRow);

            n++;
        }
        end = DateTime.Now;
        System.TimeSpan diff = end.Subtract(start);
        label2.Text = diff.Seconds.ToString();
        label4.Text = diff.Milliseconds.ToString();
        dataGridView1.DataSource = myTable;
    }

    //create assy at runtime in memory
    private void button4_Click(object sender, EventArgs e)
    {
        //build the assembly
        Type myType = CreateDynRow();

        Type listType = typeof(List<>);

        Type myListType = listType.MakeGenericType(myType);

        IList myTable = (IList)Activator.CreateInstance(myListType);

        FieldInfo piT = myType.GetField("t");
        FieldInfo piVf = myType.GetField("vf");
        FieldInfo piIm = myType.GetField("im");

        ValueType aRow = (ValueType)Activator.CreateInstance(myType);

        int n = 0;
        start = DateTime.Now;
        while (n < 100000)
        {
            piT.SetValue(aRow, 1 * n);
            piVf.SetValue(aRow, 2.0);
            piIm.SetValue(aRow, 4.0);
            myTable.Add(aRow);

            n++;
        }
        end = DateTime.Now;
        System.TimeSpan diff = end.Subtract(start);
        label2.Text = diff.Seconds.ToString();
        label4.Text = diff.Milliseconds.ToString();
        dataGridView1.DataSource = myTable;
    }

Answer 1

It’s not (primarily) the dynamic creation: it’s the use of reflection (FieldInfo.SetValue) that makes the button3 and button4 versions slower than when the calls can be compiled in.

A possible way around this is to declare an interface that your code can compile against, and have the dynamic type implement this interface. You’ll still take a small hit instantiating and querying the dynamic type for that interface via reflection, but after that it should be as fast as the “static” references.