Synchronization with mutex problem, please help!

[daoanhvu]

Hi All,

I use a mutex to synchronize device context between threads.

I create mutex from the main thread as follow:

 g_displayMutex = CreateMutex(NULL, FALSE, L"DiplayMutex");

The thread's routine is defined as follow:

DWORD WINAPI StartMoving(void *param)
{
	CMyBall *p = (CMyBall*)param;
	DWORD flag = 0;
	while(p->Alive())
	{
		flag = WaitForSingleObject(g_displayMutex, 100);

		switch(flag)
		{
			case WAIT_OBJECT_0:
				p->move();
				p->draw(g_memDC);
				InvalidateRect(g_hWnd, NULL, true);
				UpdateWindow(g_hWnd);	

				ReleaseMutex(g_displayMutex);
				Sleep(20);
				break;

			case WAIT_ABANDONED:
				p->SetAlive(FALSE);
				return 1;
		}
	}
	
	return 0;
}

When user close the program, I wait for the mutex and set the living status of object to false:

case WM_DESTROY:

			if(WaitForSingleObject(g_displayMutex, INFINITE) != WAIT_OBJECT_0)
			{
				MessageBox(NULL, L"Wait fail", L"WM_DESTROY", MB_OK);
			}

			for(int i=0; i<gNumOfBall; i++)
				gBalls[i].SetAlive(FALSE);
			ReleaseMutex(g_displayMutex);

			WaitForMultipleObjects(gNumOfBall, gThreads, TRUE, INFINITE);

			for(int i=0;i<gNumOfBall;i++)
			{
				CloseHandle(gThreads[i]);
			}

			CloseHandle(g_displayMutex);

			//Release memory DC here
			ReleaseMemoryDC(hWnd);
                        ...
                        PostQuitMessage(0);
break;

The problem is the process does not end when the program closed. I have to press "Stop Debug" from VS (I use VS2010) to force it stop.

Please friends, help me on this problem, many thanks in advance!
Nautilus