Thread Terminates after 2 Minutes without any reason

Hi friends,

I wrote a little program to practice multi-threading in VC2005. Everything seems to be OK, but it terminate after about 2 minutes with returned code 0 (0x0).

This is my thread routine:

Code:

DWORD WINAPI StartMoving(void *param)
{
	CMyBall *p = (CMyBall*)param;

	while(!isExited)
	{
		p->move();

		//If the ball reachs bottom, top, left or right border, it will turn out
		if((p->x < p->R)||(p->x > (rectClient.right - rectClient.left)-p->R))
			p->vx = -p->vx;

		if((p->y < p->R)||(p->y > (rectClient.bottom - rectClient.top)-p->R))
			p->vy = -p->vy;

		WaitForSingleObject(g_displayMutex, INFINITE);

		InvalidateRect(g_hWnd, NULL, 0);
		Sleep(20);

		ReleaseMutex(g_displayMutex);
	}
	return 0;
}

Any explanation will be appreciated.
Thanks