parallel c++ join in .net 1.1

Question

I'm trying to spawn and then join two threads using MS VS 6.0 (2003), MS .NET Framework 1.1.

The following seems to be a reasonable solution:

CWinThread* thread1 = AfxBeginThread(worker, &parallel_params);
CWinThread* thread2 = AfxBeginThread(worker, &parallel_params);
WaitForSingleObject(thread1->m_hThread, INFINITE);
WaitForSingleObject(thread2->m_hThread, INFINITE);

but my main concern has to do with this statement in the documentation: "If this handle is closed while the wait is still pending, the function's behavior is undefined." When do handles get closed? Does ending the worker proc close the handle? If so, am I in trouble? Is this really a reasonable solution??

Answer 1

In order to be able to safely wait on the thread's handle, you should:

1. Start the thread suspended
2. Set the m_bAutoDelete member to false, so that the returned CWinThread* is not deleted automatically once the thread exits
3. Resume the thread
4. And finally wait on the handle the way you do.

Alternatively, you can start the thread suspended, then duplicate the handle, leave m_bAutoDelete as is, and finally wait on the new handle. This way the CWinThread* will indeed be deleted, but you'll still have a handle to wait on. Also, don't forget to close the handle once your done waiting on it.

If you leave your code as is, you might not even get to wait on a closed handle. If the thread exits you get to the wait function, the CWinThread* pointer might point to a deleted object, and you'll get an exception.