Why can't my MFC app exit completely?

2
votes

I made a MFC application which probably has two threads, one for receiving data from a socket using UDP protocol and one is the main thread of MFC app. While any data is received some objects, created in the main thread by new operator, would be notified to fetch the data through apply the observer design pattern. The problem is that sometimes after I clicked the close system button, the GUI of the app disappeared, but its process can still be found in the Task Manager. If I stop the data source (UDP client) this problem would never happen. Other important and maybe helpful information is listed below:

  1. The Observer design pattern was implemented with STL container list. I have used the critical section protection in the Attach, Detach and Notify functions.
  2. I deleted the observer objects before closing the UDP socket.
  3. The data transfer rate may be a little faster than process data, because after closing the data source the data process is still working.

I can't figure out what lead my app can not exit completely. Please give me some clues.

3
c++multithreadingmfc
Post some code from where the second thread is started. - Luchian Grigore
The second thread is created by the socket object. I got the socket library from codeproject, I don't think there would be any mistake. - gomypig
Run the program under debugger. Close main window. Execute Break command, open Threads window and see what happens. BTW, library downloaded from CodeProject may have bugs, or your own code is missing some cleanup function call. - Alex F
I think I have found the causes of the problem. While I debug my app following your method, I found the main thread always blocks in the COleDispatchDriver::ReleaseDispatch function. And the next line blow this function is ccccccc() in the thread window of Visual Studio 2008.I suppose it must be that as the activex objects, I created dynamically before, being deleted the work thread are still operating these objects. So the dispatch operator can't finish properly. How can I fix it? How to delete an activex control dynamically properly and completely? - gomypig

3 Answers

1
votes

This is usually caused by a thread you created and not exit it programmatically when you exit the appliation. There must be a while clause in your thread. The way to find where it is still running is:

  1. use debug mode to start you application and click the exit button the top right corner to exit it.

  2. Check from task manager and see if it is still running

  3. if it is, excute Debug->Break All,

  4. Open threads windows, double click each thread, you will find where your code is still looping.

0
votes

Typically a process won't terminate because there's still a foreground thread running somewhere. You must ensure that your socket library isn't running any thread when you want to close your application.

0
votes

First thing, with MFC, please use the notification based methods to get notifications on message arrivals, connections etc. So you can get rid of threads if you have.

It's quite easy to attache to a debugger and Break see which threads are existing and waiting for what.

Alternatively you can use ProcessExplorer with proper symbol configuration to see the call stacks of the threads available for the particular process.

The application can two kind of issues to exit, one could be infinite loop and other might be waiting/deadlock (e.g. socket read command is a blocking call). You can easily deduce the problem by attaching to debugger.

Otherwise please provide further information about the threads, code snippet possible.