使用调试器逐步执行程序需要很长时间

When I debug my program by stepping through it, it sometimes takes a long time for the step to finish. This was not happening in the beginning of the project so most likely it is due to something I have added. Could you give me pointers as to how to remedy this. I did notice one of the problems was due to the main thread trying to paint a widget. My application is multi-threaded (1 background thread and 1 main thread) so I am wondering if it has something to do with that. Your comments are appreciated.When I debug my program by stepping through it,