While your code is being executed, how to interact with UI

Question

protected void btnSaveV_Click(object sender, EventArgs e)
{
    main1();
}

public void main1()
{
    main2();
}

public void main2()
{
    main1();
}

After click on stop button want to stop this nested method looping--unable to interact because may be "While your code is being executed, the user cannot interact with your user interface.". please how to resolve it.