Correct way of checking if threads are done?

You can use WaitForMultipleObjects to wait for the threads to finish in primary thread.

What you want to have a look at is thread synchronization techniques - luckily there is quite a bit of information on MSDN which can probably help you out. It's likely you'll want to use Events and WaitHandles here's the main stuff on MSDN: http://msdn.microsoft.com/en-us/library/ms681924%28v=VS.85%29.aspx there are a number of examples.

There's also some info on synchronization in MFC (which may or may not prove helpful, added for reference purposes): http://msdn.microsoft.com/en-us/library/975t8ks0%28VS.71%29.aspx

I've done a bit of searching, but I've had a hard time trying to track down some helpful info for you which doesn't use the MFC implementation. There's a good tutorial here ( http://www.informit.com/library/content.aspx?b=Visual_C_PlusPlus&seqNum=149 ) but, again, using MFC. You could take a look at the MFC implementation of mutexes though as a start.

So, you'd need to get familiar with synchronization functions and structures - all covered here on MSDN: http://msdn.microsoft.com/en-us/library/ms686679%28v=VS.85%29.aspx

Use _beginthreadex instead. Both _beginthread and _beginthreadex return a thread handle, but the thread started with _beginthread automatically closes its handle when it finishes, so using it for synchronization is not reliable.

Thread handle can be used with one of the synchronization functions of Win32, such as WaitForSingleObject or WaitForMultipleObjects.

When done, handles returned by _beginthreadex must be closed with CloseHandle().