CView::UpdateData causes Debug Assertion
SOECC01.NUEBEL01 -- SOECC01.NUEBEL01@ssw.alcoa.com
Monday, March 17, 1997
Environment: NT 4.0, VC 4.2b
Hi!
Scenario: I`m displaying information read from the serial port
in an edit control of my view (SDI-application).
A seperate thread, that reads the serial port calls the following
global function, which causes a debug assertion:
void UserCallBack( CString& result, CString& status )
{
CWinApp* pApp;
CMyView* pView;
// determine current application
pApp = AfxGetApp();
// determine current view
CMainFrame* pFrame = (CMainFrame*)pApp->m_pMainWnd;
pView = (CMyView*) pFrame->GetActiveView();
pView->myVar1 = result;
pView->myVar2 = status;
pView->UpdateData(FALSE);
}
UpdateData should update two edit controls, which are associated with
myVar1 and myVar2, but this code causes a Debug Assertion.
When calling this function from a button on the view, instead of from a
separate thread, there is no problem.
Any idea, what is wrong with my code?
Thanks in advance.
-- Markus Nuebel
============================================================================
Markus Nuebel | voice: +49 +2921 970-354
ALCOA Automotive Structures GmbH |
Overweg 24 | e-Mail: SOECC01.NUEBEL01@SSW.ALCOA.COM
59471 Soest , Germany | fax: +49 +2921 970-499
============================================================================
Dan Kirby -- dkirby@accessone.com
Wednesday, March 19, 1997
[Mini-digest: 3 responses]
Hi,
You never mention what/where the assert is. I'm guessing the problem is
due to the fact that you have a secondary thread which is calling the
callback. As a result, remember that the CWnd-to-HWnd map is stored on a
per thread basis in the module thread state. If any functions references
this map, you will most likely get an assert. There may be something else
going on but you'll need to track down the assert and provide more
information.
--dan
----------
> From: SOECC01.NUEBEL01
> To: mfc-l@netcom.com
> Subject: CView::UpdateData causes Debug Assertion
> Date: Monday, March 17, 1997 7:47 AM
>
>
>
> Environment: NT 4.0, VC 4.2b
>
> Hi!
>
> Scenario: I`m displaying information read from the serial port
> in an edit control of my view (SDI-application).
>
> A seperate thread, that reads the serial port calls the following
> global function, which causes a debug assertion:
>
> void UserCallBack( CString& result, CString& status )
>
> {
>
>
> CWinApp* pApp;
> CMyView* pView;
>
>
>
> // determine current application
>
>
> pApp = AfxGetApp();
>
>
>
> // determine current view
> CMainFrame* pFrame = (CMainFrame*)pApp->m_pMainWnd;
>
>
> pView = (CMyView*) pFrame->GetActiveView();
>
> pView->myVar1 = result;
> pView->myVar2 = status;
>
>
> pView->UpdateData(FALSE);
>
>
> }
>
> UpdateData should update two edit controls, which are associated with
> myVar1 and myVar2, but this code causes a Debug Assertion.
>
> When calling this function from a button on the view, instead of from a
> separate thread, there is no problem.
>
> Any idea, what is wrong with my code?
>
> Thanks in advance.
>
> -- Markus Nuebel
>
>
============================================================================
> Markus Nuebel | voice: +49 +2921 970-354
> ALCOA Automotive Structures GmbH |
> Overweg 24 | e-Mail:
SOECC01.NUEBEL01@SSW.ALCOA.COM
> 59471 Soest , Germany | fax: +49 +2921 970-499
>
============================================================================
>
>
>
>
>
-----From: Marcel de Vries
hi,
You're telling that you call this function in onother thread. This is
causing the problem. It is not posible to acces a CWND from onother
thread that has not created the window. This is because there is a
mapping in Thread local storage from a HWND do a CWND object.
This is explaind in the article in the online help.
I included it here to save your time finding it :
+++++++++++++++++++++++++++++++++++++++++++++
Windows Handle Maps
As a general rule, a thread can access only MFC objects that it created.
This is because temporary and permanent Windows handle maps are kept in
thread local storage to ensure protection from simultaneous access from
multiple threads. For example, a worker thread cannot perform a
calculation and then call a document's UpdateAllViews member function to
have the windows that contain views on the new data modified. This will
have no effect at all, because the map from HWND objects to CWND is
local to the primary thread. This means that one thread may have a
mapping from a Windows handle to a C++ object, but another thread may
map that same handle to a different C++ object. Changes made in one
thread would not be reflected in the other.
There are several ways around this problem. The first is to pass
individual handles (such as an HWND) rather than C++ objects to the
worker thread. The worker thread then adds these objects to its
temporary map by calling the appropriate FromHandle member function. You
could also add the object to the thread's permanent map by calling
Attach, but this should be done only if you are guaranteed that the
object will exist longer than the thread.
Another method is to create new user-defined messages corresponding to
the different tasks your worker threads will be performing and post
these messages to the application's main window using ::PostMessage.
This method of communication is similar to two different applications
conversing except that both threads are executing in the same address
space.
For more information on handle maps, see Technical Note 3. For more
information on thread local storage, see Thread Local Storage and Using
Thread Local Storage in the Win32 Programmer's Reference.
++++++++++++++++++++++++++++++++++++++++++++++++
>----------
>From: SOECC01.NUEBEL01[SMTP:SOECC01.NUEBEL01@ssw.alcoa.com]
>Sent: Monday, March 17, 1997 4:47 PM
>To: mfc-l@netcom.com
>Subject: CView::UpdateData causes Debug Assertion
>
>
>
>Environment: NT 4.0, VC 4.2b
>
>Hi!
>
>Scenario: I`m displaying information read from the serial port
>in an edit control of my view (SDI-application).
>
>A seperate thread, that reads the serial port calls the following
>global function, which causes a debug assertion:
>
>void UserCallBack( CString& result, CString& status )
>
>{
>
>
> CWinApp* pApp;
> CMyView* pView;
>
>
>
> // determine current application
>
>
> pApp = AfxGetApp();
>
>
>
> // determine current view
> CMainFrame* pFrame = (CMainFrame*)pApp->m_pMainWnd;
>
>
> pView = (CMyView*) pFrame->GetActiveView();
>
> pView->myVar1 = result;
> pView->myVar2 = status;
>
>
> pView->UpdateData(FALSE);
>
>
>}
>
>UpdateData should update two edit controls, which are associated with
>myVar1 and myVar2, but this code causes a Debug Assertion.
>
>When calling this function from a button on the view, instead of from a
>separate thread, there is no problem.
>
>Any idea, what is wrong with my code?
>
>Thanks in advance.
>
>-- Markus Nuebel
>
>============================================================================
> Markus Nuebel | voice: +49 +2921 970-354
> ALCOA Automotive Structures GmbH |
> Overweg 24 | e-Mail: SOECC01.NUEBEL01@SSW.ALCOA.COM
> 59471 Soest , Germany | fax: +49 +2921 970-499
>============================================================================
>
>
>
>
>
>
-----From: Mike Blaszczak
At 10:47 3/17/97 EST, SOECC01.NUEBEL01 wrote:
>Environment: NT 4.0, VC 4.2b
>UpdateData should update two edit controls, which are associated with
>myVar1 and myVar2, but this code causes a Debug Assertion.
>Any idea, what is wrong with my code?
No real idea whatsoever. Since you don't bother to tell us exactly what
assertion failed, there's no way we can know exactly what problem you're
experiencing. The assertion message has a line number and a file name
in it. We'd need that information at a scraping bare minimum. A stack
trace leading to the point of the assertion would make it much easier
to answer your question.
>When calling this function from a button on the view, instead of from a
>separate thread, there is no problem.
Perhaps the problem is simply that you can't do UpdateView() on a view
that's not owned by the calling thread. But I can't be sure: since
you've provided no evidence, this is just a guess.
>Thanks in advance.
Please make me a chocolate shake. Thanks in advance.
[Moderator's note: Poof! You're a chocolate shake. And, you're welcome...]
.B ekiM
http://www.nwlink.com/~mikeblas/
These words are my own. I do not speak on behalf of Microsoft.
One is too many and a million is not enough.
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