clistctrl threadsafe access

I have clist control in my CListView based class. I also defined a function AddMsg to add item to the clist control. This function will be called from many places (threads) in the problem. I wan to have a threadsafe access to the control. I tried to use CCriticalSection for it, but the program will lock up, I think some deadlock is happening. How can I solve it.


CCriticalSection m_CriticalSection;

void CMyView::AddMsg(CString &msg)
{
m_CriticalSection.Lock();

do list control access...
m_CriticalSection.Unlock();
}

how are you accessing this function from the thread(s)? it is not advisible to directly access MFC objects from a thread, you should rather PostMessage() from the thread. In the message handler do whatever you have to. This site has a very good FAQ section on threads, which I recommend checking out.

[ moved thread ]

Thanks for the reply, but if I use PostMessage(), since I will pass the local CString pointer, the pointer will not be valid by the time the message is being pocessed. What should I do?

Quote:

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Originally Posted by mwong7025

Thanks for the reply, but if I use PostMessage(), since I will pass the local CString pointer, the pointer will not be valid by the time the message is being pocessed. What should I do?

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you can try sommething like this:

Code:

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in the thread:

CString strToSend = new CString("From thread");

::PostMessage(m_handleToYourClass, WM_YOUR_CUSTOM_MESSAGE, 0, reinterpret_cast<LPARAM>strToSend);

in the message handler:

CYourClass::OnMessage(WPARAM wParam, LPARAM lParam)
{   
        std::auto_ptr <CString> strFromThread(reinterpret_cast <CString *>(lParam));

        // do something with strFromThread
        // additionally there is no need to delete [] anything
}

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I'm not so familiar with auto-pointer, but shouldn't this line

Code:

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::PostMessage(m_handleToYourClass, WM_YOUR_CUSTOM_MESSAGE, 0,
    reinterpret_cast<LPARAM>strToSend);

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be

Code:

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::PostMessage(m_handleToYourClass, WM_YOUR_CUSTOM_MESSAGE, 0,
    reinterpret_cast<LPARAM>&strToSend);

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Mike

You cannot use the CListCtrl class from multiple threads because MFC uses thread-local storage to map window handles to MFC objects.

Try to use the window handle of the list control instead of the CListCtrl class. You may use the ListView_* macros defined in commctrl.h that makes most of the work almost painless.

Ah, and by the way: Consider using a CSingleLock with your critical section to wrap syncronization and support exception safety, e.g. like this:

Code:

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{
        // Lock critical section.
        CSingleLock sl(&m_CriticalSection, TRUE);


        // Insert new item into list control.
        LVITEM lvItem;
        memset(&lvItem,0,sizeof(LVITEM));
        lvItem.iItem = 0x0fffffff;
        const int ciItem(ListView_InsertItem(m_hListCtrl, &lvItem));
}

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