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UpdateAllViews Crashes My App

DizZzM
DizZzM asked
on
Medium Priority
314 Views
Last Modified: 2013-11-20
Hi Experts -

Easy question (hopefully) - developing a serial data monotoring utility. Every time I get new data on the bus I want to  display it in the main window. The set-up I have now is - the user hits a run button which calls onRun() from myDoc class - it opens up the serial port and it goes into an infinite while loop that polls the bus. If there is data on the bus - then it reads it and it calls UpdateAllViews(NULL) to make a call to pDC->TextOut(). This is crashing my application - any ideas?

Also - is it possible to put a flag on that infinite loop that'll get reset by another button (call it Stop)? So for example...

void MyDoc::OnCommandStop()
{
      stop_recv_flag = 1;
}

void MyDoc::OnCommandRun()
{
      while(!stop_recv_flag)
      {
            status = read_bus (data);
            if (status == ARS_GOTDATA)
            {
                 UpdateAllViews(NULL);      
            }                        
      }

      stop_recv_flag = 0;
      
      
}

So if I  hit the stop button to call OnStop will it break the while loop if stop_recv_flag is a global variable?
Comment
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Author

Commented:
Hi Experts -

Found the solution, just needed to add

AfxGetApp()->PumpMessage();

inside of the while loop.

The 2nd question is still an open issue however so the points are still up for grabs. For some reason, when I hit OnStop(), the global 'stop_recv_flag' does get set but then I get an application error and it shuts down. I would have thought OnRun would have read the correct new value and kicked out of the loop nicely.

Any ideas?
mahesh1402IT Professional
Top Expert 2005

Commented:
>>then I get an application error

What kind of error you are getting ?

-MAHESH
AndyAinscowFreelance programmer / Consultant
CERTIFIED EXPERT
Commented:
I guess that
void MyDoc::OnCommandStop()
{
     stop_recv_flag = 1;
}
is never being called when you hit the stop button.  Try putting a breakpoint onto the  stop_recv_flag = 1; and seeing if it is reached.



also
void DoEvents()
{  
      MSG msg;  
      while ( ::PeekMessage(&msg, NULL, 0, 0, PM_REMOVE ) )
      {  
            ::TranslateMessage(&msg);
            ::DispatchMessage(&msg);
      }
}

void MyDoc::OnCommandRun()
{
     while(!stop_recv_flag)
     {
          status = read_bus (data);
          if (status == ARS_GOTDATA)
          {
               UpdateAllViews(NULL);    
          }  
DoEvents();   <<---------------- allow the message queue to be processed                
     }

     stop_recv_flag = 0;
     
     
}

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Author

Commented:
hi mahesh - it's a sharing violation. I step through with the debugger and OnStop() does execute and stop_recv_flag does get modified. The error occurs on return. Do I need some mutex around stop_recv_flag?

The weird part is I kept developing and troubleshooting last night and I started noticing that the error does not occur every single time which makes me further believe I just need some mutex around the variable but maybe I'm wrong.

Hi Andy - thanks for your solution. Got that part working after I posted my original question with AfxGetApp()->PumpMessage();.
AndyAinscowFreelance programmer / Consultant
CERTIFIED EXPERT

Commented:
My understanding is that the PumpMessage will only force the next message in the queue to be handled.  A DoEvents type function will force all waiting messages to be handled.
mahesh1402IT Professional
Top Expert 2005

Commented:
>>The error occurs on return.

return means exactly where ? In loop ?? have you traced that ??? you may put a simple MessageBox() before UpdateAllViews to trace that...

-MAHESH

Author

Commented:
return from the OnStop() call.  I'll do some more analysis now and see if I can dig any deeper.
IT Professional
Top Expert 2005
Commented:
You have overrideen function OnUpdate() for all / any of your views ?

As said you may put messagebox before/after UpdateAllViews() to ensure its happening only when UpdateAllViews executed..

-MAHESH

Author

Commented:
Hi Guys - just ended up using a CMutex around the stop_recv_flag assignment and it worked! I'll just split the points between you guys. Thanks again!

CMutex recv_Mutex;

void MyDoc::OnCommandStop()
{
recv_Mutex
     stop_recv_flag = 1;
}

void MyDoc::OnCommandRun()
{
     while(!stop_recv_flag)
     {
          status = read_bus (data);
          if (status == ARS_GOTDATA)
          {
               UpdateAllViews(NULL);    
          }                    
     }

     stop_recv_flag = 0;
     
     
}

Author

Commented:
Sorry - got trigger happy on the send... heres the solution:

CMutex recv_Mutex;

void MyDoc::OnCommandStop()
{
     recv_Mutex.Lock;
     stop_recv_flag = 1;
     recv_Mutex.Unlock;
}

void MyDoc::OnCommandRun()
{
     while(!stop_recv_flag)
     {
          status = read_bus (data);
          AfxGetApp()->PumpMessage();

          if (status == ARS_GOTDATA)
          {
               UpdateAllViews(NULL);    
          }                    
     }

     stop_recv_flag = 0;
     
     
}
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