private static Form1 instance;
private Object logWindowLock = new Object();
delegate void SetTextCallback(string text);

public Form1()
{
    instance = this;
    InitializeComponent();
}

public static Form1 Instance
{
    get
    {
        return instance;
    }
}
// This method demonstrates a pattern for making thread-safe
// calls on a Windows Forms control.
//
// If the calling thread is different from the thread that
// created the TextBox control, this method creates a
// SetTextCallback and calls itself asynchronously using the
// Invoke method.
//
// If the calling thread is the same as the thread that created
// the TextBox control, the Text property is set directly.
public void WriteToLog(string text)
{
    // InvokeRequired required compares the thread ID of the
    // calling thread to the thread ID of the creating thread.
    // If these threads are different, it returns true.
    if (this.logWindow.InvokeRequired)
    {
        SetTextCallback d = new SetTextCallback(WriteToLog);
        this.Invoke(d, new object[] { text });
    }
    else
    {
        lock (this.logWindowLock)
        {
            this.logWindow.AppendText(DateTime.Now.ToString() + ": " + text + "\n");
            this.logWindow.ScrollToCaret();
            this.logWindow.Refresh();
        }
    }
}