I’m currently working on a program using MFC. The current third party function starts a thread after an action has been completed using MFC (ie. Checking a checkbox, which starts a MFC thread I believe).
The problem occurs when I check the checkbox, at which point the entire program hangs. I read a few interesting discussions on CProgramming and msdn, it seems that the problem occurs because the new third party thread is calling WaitToSomething() when MFC is updating a control.
Something interesting to note:
- When I debug the program, the program hangs (aka. repeatedly calls WaitToRead() ) after I check the checkbox and a new thread is trying to start
- When I run the program without debugger, the program is fine UNTIL I switch to another window (ie. Internet browser, Notepad, etc)
My hypothesis:
- check to make sure that MFC has finished updating the control before starting a new thread
If anyone has any suggestions or solutions, please leave a comment. Thanks.
Edit:
MFC is not thread-safe at object level (only at class level), so problem occurs when two threads work on the same CButton object.
Q: How do I make it thread safe?
A colleague helped me figure out what the problem was.
The reason why it was hanging is because that the control containing the checkbox is a child dialog, and when it finished updating the message never got passed up to its parent (so when 3rd party thread calls WaitFor(), the MFC thread never completes because a parent dialog thinks its child is still updating the controls).
Fix:
Under ‘Properties’ in the child dialog’s control, set the ‘Control’ flag to true (and if it has children, set the ‘Control Parent’ flag to true as well).
Hope this helps.