Длина C ++ std :: string в байтах

    private voidForm_Load(object sender, EventArgs e)
    {
        MethodInvoker mk = delegate
        {
            //your job
        };
        mk.BeginInvoke(callbackfunction, null);
    }

    private void callbackfunction(IAsyncResult res)
    {
        // it will be called when your job finishes.
    }

use MethodInvoker - самый простой способ.