Thread + AfxGetMainWnd()

[Tischnoetentoet]

Hi all,

I am creating a thread (CWinThread class);

I am only using this code:

BOOL CMyThread::InitInstance()
{
// Get parent handle
CWnd * pWnd = AfxGetMainWnd();

// Send message that we are ready
pWnd->PostMessage(WM_TASK_COMPLETE, (WPARAM)TASK_MYTHREAD);

return TRUE;
}


The problem is that pWnd is null.

I call this function like this at the end (and tried even after) OnInitDialog():

CMyThread * pMyThread = (CMyThread*)AfxBeginThread(RUNTIME_CLASS(CMyThread));


Any idea where the problem is?

[TSYS]

I believe the main window is in CWinThread::m_pMainWnd. I'm actually a little surprised that AfxGetMainWnd() didn't assert.

[Tischnoetentoet]

yes, but when I call the function AfxGetMainWnd(), I get that member variable.

Or am I tottaly wrong now??

[TSYS]

No, you're right. I'm wrong (again). You have to assign a value to CWinThread::m_pMainWnd. The following quote is from this link (http://www.murrayc.com/learning/windows/multithreading.shtml)
Threads may have a window. You may create a window in InitInstance() and assign it to CWinThread's m_pMainWnd member variable. All messages for that window will then be sent to that thread. You will have, in effect, created a window running in its own thread. Note that this technique can often lead to poor performance because sending a windows messages may halt the sender until the ::SendMessage() function returns.

[Tischnoetentoet]

I think it's not meant to be filled by the programming. I think it should be done automatically.

I've seen applications that worked perfectly and automatically!

[cilu]

If AfxGetMainWnd() is called from the application's primary thread, it returns the application's main window according to the above rules. If the function is called from a secondary thread in the application, the function returns the main window associated with the thread that made the call.

If your thread has no window attached, it returns NULL.

[Tischnoetentoet]

The thing I want to realise is this:

I have 1 dialog. From this dialog, I start several threads (CWinThread).
These threads must send a message when they are ready to the main dialog.

Then I send a message to the thread that he can stop:
pThread1->PostMessage(WM_QUIT, 0, 0);

So the thread itself does not have a window. But how can I send a message to the main dialog (the one that started the thread)?

[ovidiucucu]

The example I posted for you HERE (http://www.codeguru.com/forum/showthread.php?t=316181) works.
However, to assure that AfxGetMainWnd returns what you want, do something like this:


void CMyDialog::WhateverFunction()
{
// ...
m_pThread1 = (CThread1*)AfxBeginThread(RUNTIME_CLASS(CThread1),
THREAD_PRIORITY_NORMAL,
0,
CREATE_SUSPENDED);
m_pThread1->m_pMainWnd = this;
m_pThread1->m_pActiveWnd = this;

m_pThread1->ResumeThread();
}

[Tischnoetentoet]

:thumb: works perfect :)

[Andreas Masur]

[ Moved thread ]