private void Form1_Load(object sender, EventArgs e)
{
    Display();
}

public async void Display()
{
    int result = await GetValueAsync(123);
    this.label1.Text = "Value is : " + result;
}

public Task<int> GetValueAsync(int num)
{
    // 方法1
    return Task.Run(() =>
    {
        return DoSomething(num);
    });

    // 方法2
    return Task.Run(() =>
    {
        //DoSomething
        System.Threading.Thread.Sleep(3000);
        return num;
    });

    // 方法3
    object state = num;
    Task<int> task = new Task<int>(DoSomething, state);
    task.Start();
    return task;
}

public int DoSomething(int num)
{
    System.Threading.Thread.Sleep(3000);
    return num;
}

public int DoSomething(object state)
{
    System.Threading.Thread.Sleep(3000);
    return Convert.ToInt32(state);
}