I need to create a new thread to run program in a subDialog box.
The subDialog is a drawing function that consists of a self-defined drawing requirement and an on-paint function that initialize the self function. This subDialog calls on variables from the Main dialog to see how many objects it needs to draw.
Effect: When the Main Prog runs real-time, the sub Prog will show the number of objects simultanously.

So, in creating a thread in the main dialog, how do you create a pointer to point back the subDialog class to the main Dialog?
What do you write for the source code?

: I need to create a new thread to run program in a subDialog box.
: The subDialog is a drawing function that consists of a self-defined drawing requirement and an on-paint function that initialize the self function. This subDialog calls on variables from the Main dialog to see how many objects it needs to draw.
: Effect: When the Main Prog runs real-time, the sub Prog will show the number of objects simultanously.
:
: So, in creating a thread in the main dialog, how do you create a pointer to point back the subDialog class to the main Dialog?
: What do you write for the source code?
:

There's a few ways you can do that. One way would be to get a CWnd to the main window and use that to access the main dialog..

 // in ThreadProc
CWnd *CWndParent = AfxGetMainWnd();
 // or
CWnd *CWndParent = GetParent();

((CMyMainDialog*)CWndParent)->DoSomething();

Or the way I would do it is to pass the main dialogs CWnd to the new thread via the CreateThread's lpParameter, then I can use it in the thread.

CWinThread *pThread = AfxBeginThread(ThreadProc, (LPVOID)this, THREAD_PRIORITY_NORMAL);
 // or
HANDLE pThread = CreateThread(NULL, 0, ThreadProc, (LPVOID)this, 0, &pThreadID);

 // in ThreadProc
CWnd *CWndParent = (CWnd*)lpParam;
((CMyMainDialog*)CWndParent)->DoSomething();

To understand recursive, first you need to understand recursive

This message was edited by suhredayan at 2004-2-10 6:5:57

---

You cannot pass a CWnd object pointer like this between threads. Instead you have to pass the window handle , from which a pointer to the original object can be reconstructed using the static
CWnd::FromHandle function;

eg :

UINT int thread_func (void *arg) 
{
     HWND hwnd = (HWND)arg; 
     CWnd *pWnd = CWnd::FromHandle (hwnd); 
// proceed to use pWnd..
} 

greatest thing is to do wot others think you can't..
suhredayan@omniquad.com

What's wrong with this. It has always worked for me.

void CMyView::StartThread()
{
    AfxBeginThread(MyThread, this, THREAD_PRIORITY_BELOW_NORMAL);
    return;
}

UINT MyThread(LPVOID pParam)
{
    CMyView *pMyView = (CMyView *) pParam;
    
    ...
    ...
    ...
    
    return 0;
}

: This message was edited by suhredayan at 2004-2-10 6:5:57

---

:
: You cannot pass a CWnd object pointer like this between threads. Instead you have to pass the window handle , from which a pointer to the original object can be reconstructed using the static
: CWnd::FromHandle function;
:
: eg :
:

: UINT int thread_func (void *arg) 
: {
:      HWND hwnd = (HWND)arg; 
:      CWnd *pWnd = CWnd::FromHandle (hwnd); 
: // proceed to use pWnd..
: } 
: 

:
:
: greatest thing is to do wot others think you can't..
: suhredayan@omniquad.com
:
:
:
:

You're breaking a cardinal rule of MFC: Don't pass CWnd objects between
threads. The fact that the code happens to work is a fluke. More
complicated code would definitely be hitting asserts all over the place.

__________________________________________
greatest thing is to do wot others think you can't..
suhredayan@omniquad.com

:
:
: You're breaking a cardinal rule of MFC: Don't pass CWnd objects between
: threads. The fact that the code happens to work is a fluke. More
: complicated code would definitely be hitting asserts all over the place.
:
: __________________________________________
: greatest thing is to do wot others think you can't..
: suhredayan@omniquad.com
:
:

Ahh yes, thanks for correcting me. MSDN Technical Note TN003 (Mapping of Windows Handles to Objects) explains it very well.


To understand recursive, first you need to understand recursive

: :
: :
: : You're breaking a cardinal rule of MFC: Don't pass CWnd objects between
: : threads. The fact that the code happens to work is a fluke. More
: : complicated code would definitely be hitting asserts all over the place.
: :
: : __________________________________________
: : greatest thing is to do wot others think you can't..
: : suhredayan@omniquad.com
: :
: :
:
: Ahh yes, thanks for correcting me. MSDN Technical Note TN003 (Mapping of Windows Handles to Objects) explains it very well.
:
:
: To understand recursive, first you need to understand recursive
:
:

The way I do that is to send private messages from thread 2 to its parent thread and let the parent thread update the window, or dialog, or whatever. My program crashed bigtime the first time I attempted to update a dialog in thread #2.

: : :
: : :
: : : You're breaking a cardinal rule of MFC: Don't pass CWnd objects between
: : : threads. The fact that the code happens to work is a fluke. More
: : : complicated code would definitely be hitting asserts all over the place.
: : :
: : : __________________________________________
: : : greatest thing is to do wot others think you can't..
: : : suhredayan@omniquad.com
: : :
: : :
: :
: : Ahh yes, thanks for correcting me. MSDN Technical Note TN003 (Mapping of Windows Handles to Objects) explains it very well.
: :
: :
: : To understand recursive, first you need to understand recursive
: :
: :
:
: The way I do that is to send private messages from thread 2 to its parent thread and let the parent thread update the window, or dialog, or whatever. My program crashed bigtime the first time I attempted to update a dialog in thread #2.
:
:


Ok here's what I'm doing..
I'm creating a new thread and passing it the main Dialog's 'm_hWnd' member. In the new thread, I'm creating a new CWnd object using CWnd::FromHandle() on the HWND I passed to it. When I want to notify the main dialog of something, I use MyNewCWnd->PostMessage() with a user-defined message and a user-defined message handler in the main thread to handle it.

Now, if MyNewCWnd->PostMessage() works fine, shouldn't I also be able to call a function directly.. ex: MyNewCWnd->SomeFunction(); or should I only stick to using PostMessage()?




To understand recursive, first you need to understand recursive

: : : :
: : : :
: : : : You're breaking a cardinal rule of MFC: Don't pass CWnd objects between
: : : : threads. The fact that the code happens to work is a fluke. More
: : : : complicated code would definitely be hitting asserts all over the place.
: : : :
: : : : __________________________________________
: : : : greatest thing is to do wot others think you can't..
: : : : suhredayan@omniquad.com
: : : :
: : : :
: : :
: : : Ahh yes, thanks for correcting me. MSDN Technical Note TN003 (Mapping of Windows Handles to Objects) explains it very well.
: : :
: : :
: : : To understand recursive, first you need to understand recursive
: : :
: : :
: :
: : The way I do that is to send private messages from thread 2 to its parent thread and let the parent thread update the window, or dialog, or whatever. My program crashed bigtime the first time I attempted to update a dialog in thread #2.
: :
: :
:
:
: Ok here's what I'm doing..
: I'm creating a new thread and passing it the main Dialog's 'm_hWnd' member. In the new thread, I'm creating a new CWnd object using CWnd::FromHandle() on the HWND I passed to it. When I want to notify the main dialog of something, I use MyNewCWnd->PostMessage() with a user-defined message and a user-defined message handler in the main thread to handle it.
:
: Now, if MyNewCWnd->PostMessage() works fine, shouldn't I also be able to call a function directly.. ex: MyNewCWnd->SomeFunction(); or should I only stick to using PostMessage()?
:
:
:
:
: To understand recursive, first you need to understand recursive
:
:

The object maps are thread-local. ie, if you are in a thread and do a CWnd::FromHandle you will get a new, temporary window object which is not the same C++ object that represented your class initially. Thus this is always fatal in a thread.

instead u can use
CMyWindowClass * me =
(CMyWindowClass *)CWnd::FromHandlePermanent(hWnd);
to get the permanent handle. But only if you actually created the window in that UI-thread itself.

so i feel its better to use stober's idea of sending private messages to the parent thread


__________________________________________
greatest thing is to do wot others think you can't..
suhredayan@omniquad.com

: : : The way I do that is to send private messages from thread 2 to its parent thread and let the parent thread update the window, or dialog, or whatever. My program crashed bigtime the first time I attempted to update a dialog in thread #2.
: : :
: : :
: :
: :
: : Ok here's what I'm doing..
: : I'm creating a new thread and passing it the main Dialog's 'm_hWnd' member. In the new thread, I'm creating a new CWnd object using CWnd::FromHandle() on the HWND I passed to it. When I want to notify the main dialog of something, I use MyNewCWnd->PostMessage() with a user-defined message and a user-defined message handler in the main thread to handle it.
: :
: : Now, if MyNewCWnd->PostMessage() works fine, shouldn't I also be able to call a function directly.. ex: MyNewCWnd->SomeFunction(); or should I only stick to using PostMessage()?
: :
: :
: :
: :
: : To understand recursive, first you need to understand recursive
: :
: :
:
: The object maps are thread-local. ie, if you are in a thread and do a CWnd::FromHandle you will get a new, temporary window object which is not the same C++ object that represented your class initially. Thus this is always fatal in a thread.
:
: instead u can use
: CMyWindowClass * me =
: (CMyWindowClass *)CWnd::FromHandlePermanent(hWnd);
: to get the permanent handle. But only if you actually created the window in that UI-thread itself.
:
: so i feel its better to use stober's idea of sending private messages to the parent thread
:
:
: __________________________________________
: greatest thing is to do wot others think you can't..
: suhredayan@omniquad.com
:
:



I'm thinking it's best to simply pass the new thread the main window's m_hWnd, and in the thread use ::PostMessage((HWND)lpParam, WM_SOME_MESSAGE);

What method of sending 'private messges' do you use Stober?





To understand recursive, first you need to understand recursive

This message was edited by stober at 2004-2-13 4:52:25

---

:
: What method of sending 'private messges' do you use Stober?
:

I use CreateThread() to create thread #2. The 4th parameter ("ThreadParameter") is the current thread ID obtained by calling GetCurrentThreadId().

The new thread calls PostThreadMessage() with the parent's threadID from the thread's argument.

:
: What method of sending 'private messges' do you use Stober?
:

:I use CreateThread() to create thread #2. The 4th parameter
:("ThreadParameter") is the current thread ID obtained by calling
: GetCurrentThreadId().

:The new thread calls PostThreadMessage() with the parent's threadID from the thread's argument.
:


Be carefule that MFC will not dispatch PostThreadMessage() to message or command handlers.You will have to override PreTranslateMessage() function of your CWinApp-derived class.

Also Messages sent to a UI thread through PostThreadMessage will be lost if the messages are posted while the user is manipulating a window owned by the thread.So Rather than using PostThreadMessage to post messages to a UI thread, use PostMessage to post messages to a window owned by that thread.


__________________________________________
greatest thing is to do wot others think you can't..
suhredayan@omniquad.com

: :
: : What method of sending 'private messges' do you use Stober?
: :
:
: :I use CreateThread() to create thread #2. The 4th parameter
: :("ThreadParameter") is the current thread ID obtained by calling
: : GetCurrentThreadId().
:
: :The new thread calls PostThreadMessage() with the parent's threadID from the thread's argument.
: :
:
:
: Be carefule that MFC will not dispatch PostThreadMessage() to message or command handlers.You will have to override PreTranslateMessage() function of your CWinApp-derived class.
:
: Also Messages sent to a UI thread through PostThreadMessage will be lost if the messages are posted while the user is manipulating a window owned by the thread.So Rather than using PostThreadMessage to post messages to a UI thread, use PostMessage to post messages to a window owned by that thread.
:
:

The parent thread catches the message in PreTranslateMessage() and then reposts with PostMessage() or takes other appropriate action

:
: The parent thread catches the message in PreTranslateMessage() and then reposts with PostMessage() or takes other appropriate action
:


But stober still the threat of loosing the message is there b'coz its send to a user interface thread using PostThreadMessage().
(Ref : MSDN ->ID: Q183116)
Wot about sending the message directly to the window of the main thread using PostMessage() function ..

suhredayan@omniquad.com
__________________________________________
greatest thing is to do wot others think you can't..

:
:
: But stober still the threat of loosing the message is there b'coz its send to a user interface thread using PostThreadMessage().
: (Ref : MSDN ->ID: Q183116)
: Wot about sending the message directly to the window of the main thread using PostMessage() function ..
:


I'm sending it to CWinApp-derived class, which is not a window.

Here are some additional thoughts on this: And read the reader's comments at the end of the article.

http://www.codeproject.com/tips/gbTestSDI.asp#xx718454xx

and here is another, better article
http://www.codeguru.com/misc/lenop.html

I haven't been following this conversation completely, but I thought I would try to give a suggestion. I have a CFormView which executes a thread every minute. If a certain situation occurs, I update a text box on the CFormView. Here is how I do it.

Thread that will post a message to CMainFrame

UINT MyThread(LPVOID pParam)
{
    ::PostMessage(AfxGetMainWnd()->m_hWnd, WM_MY_MSG, NULL, pParam);
    return 0;
}

Thread that will post a message to CFormView

LRESULT CMainFrame::OnMyMsg(WPARAM wParam, LPARAM lParam)
{
	GetActiveView()->PostMessage(WM_MY_MSG, wParam, lParam);
	return 0;
}

CFormView

LRESULT CMyFormView::OnMyMsg(WPARAM wParam, LPARAM lParam)
{
    // Update text box
    ....
    .... 
    ....
    return 0
}

I hope this helps. If not, just ignore me.




: :
: :
: : But stober still the threat of loosing the message is there b'coz its send to a user interface thread using PostThreadMessage().
: : (Ref : MSDN ->ID: Q183116)
: : Wot about sending the message directly to the window of the main thread using PostMessage() function ..
: :
:
:
: I'm sending it to CWinApp-derived class, which is not a window.
:
: Here are some additional thoughts on this: And read the reader's comments at the end of the article.
:
: http://www.codeproject.com/tips/gbTestSDI.asp#xx718454xx
:
: and here is another, better article
: http://www.codeguru.com/misc/lenop.html
:

I am just wondering,

if there is any particular reason, that PostMessage() should be used, but not SendMessage(). In my multi-threaded application, I have always used SendMessage() and check the return value for successfully corresponding function calls. In my knowledge, it is safe to manipulate variables/objects (via function calls) between threads using it. Is it correct?

J.B.

: I haven't been following this conversation completely, but I thought I would try to give a suggestion. I have a CFormView which executes a thread every minute. If a certain situation occurs, I update a text box on the CFormView. Here is how I do it.
:
: Thread that will post a message to CMainFrame
:

: UINT MyThread(LPVOID pParam)
: {
:     ::PostMessage(AfxGetMainWnd()->m_hWnd, WM_MY_MSG, NULL, pParam);
:     return 0;
: }
: 

:
:
: Thread that will post a message to CFormView
:

: LRESULT CMainFrame::OnMyMsg(WPARAM wParam, LPARAM lParam)
: {
: 	GetActiveView()->PostMessage(WM_MY_MSG, wParam, lParam);
: 	return 0;
: }
: 

:
: CFormView
:

: LRESULT CMyFormView::OnMyMsg(WPARAM wParam, LPARAM lParam)
: {
:     // Update text box
:     ....
:     .... 
:     ....
:     return 0
: }
: 

:
: I hope this helps. If not, just ignore me.

: I am just wondering,
:
: if there is any particular reason, that PostMessage() should be used, but not SendMessage(). In my multi-threaded application, I have always used SendMessage() and check the return value for successfully corresponding function calls. In my knowledge, it is safe to manipulate variables/objects (via function calls) between threads using it. Is it correct?
:
: J.B.


check the following article b4 comin to any conclusion..
http://www.codeproject.com/dialog/messagemgmt.asp

suhredayan@omniquad.com
__________________________________________
greatest thing is to do wot others think you can't..