Re: Threads and Messages - C / C++ / MFC Discussion Boards

Steen Krogsgaard21-Oct-02 23:34

21-Oct-02 23:34

Are you sure about that? When you SendMessage you call the WndProc directly, bypassing the pump. So SendMessage would be in the context of the worker thread, while PostMessage would be in the context of the main thread (which runs the message pump). This is also the way COM handles a call to a STA component (by posting messages instead of calling the components interfaces directly).

Of course, I may be wrong Wink | ;-)

Cheers
Steen.

"To claim that computer games influence children is ridiculous. If Pacman had influenced children born in the 80'ies we would see a lot of youngsters running around in dark rooms eating pills while listening to monotonous music"

Re: Threads and Messages

Joaquín M López Muñoz21-Oct-02 23:45

Joaquín M López Muñoz

21-Oct-02 23:45

Are you sure about that?

I'm 100% sure, if you pardon my arrogance. SendMessage only bypasses the message pump if issued from the same thread that attends the message. Otherwise, the message is queued as usual and the caller thread blocks until the target thread processes the message.
As a side note, using SendMessage from worker threads is likely, if no care is taken, to result in deadlocks.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: Threads and Messages

Steen Krogsgaard21-Oct-02 23:55

Steen Krogsgaard

21-Oct-02 23:55

Relaying facts is not arrogance! I should have read the MSDN entry on SendMessage more carefully:
If the specified window was created by the calling thread, the window procedure is called immediately as a subroutine. If the specified window was created by a different thread, the system switches to that thread and calls the appropriate window procedure. Messages sent between threads are processed only when the receiving thread executes message retrieval code. The sending thread is blocked until the receiving thread processes the message.
No doubt here. I stand corrected Blush | :O

. But at least I was right on the "I could be wrong"-part Smile | :)

Re: Threads and Messages

Joaquín M López Muñoz22-Oct-02 0:19

Joaquín M López Muñoz

22-Oct-02 0:19

Well, as happens so often, 100% sureness is a hard position to maintain Smile | :)

As for the thread context switch, there's still no doubt about it. What I'm not so sure is whether the message sent gets queued or not. My hunch, after re-reading the docs, is that it is not, so it surpasses all other messages currently queued in the target thread. Most of the time this is of little relevance, I guess.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: Threads and Messages

Hans Ruck22-Oct-02 0:36

Hans Ruck

22-Oct-02 0:36

Joaquín M López Muñoz wrote:
I'm not so sure is whether the message sent gets queued or not

It doesn't (checked and 100% sure Smile | :)

).

rechi

Re: Threads and Messages

Joaquín M López Muñoz22-Oct-02 0:39

Joaquín M López Muñoz

22-Oct-02 0:39

Thanx for the info! How did you do the test (just curious)?

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Re: Threads and Messages

Hans Ruck22-Oct-02 1:01

Hans Ruck

22-Oct-02 1:01

I've created a SDI application with a menu item used to start the worker.

The code:

void CMainFrame::OnFileThread() // menu item
{
  DWORD *th=new DWORD;
  HANDLE h=::CreateThread(NULL, 0, ThreadProc_, m_hWnd,
    0, th);

  Sleep(3000);
  delete th;
}

DWORD WINAPI ThreadProc_(
  LPVOID lpParameter   // thread data
)
{
  MSG msg;

  TRACE("in thread proc\n");
  ::PostMessage((HWND)lpParameter, WM_DUMMY3, 0, 0); // queued
  ::SendMessage((HWND)lpParameter, WM_DUMMY2, 0, 0); // calls Func2, a handler

  return 0;
}

LRESULT CMainFrame::Func2(WPARAM, LPARAM) // treating WM_DUMMY2
{
  MSG msg;

  TRACE("in dummy2\n");
  while (::GetMessage(&msg, NULL, 0, 0))
    if (msg.message==WM_DUMMY3)
    {
      TRACE("found dummy3\n");
      return 0;
    }

  return 0;
}

And the debug output:

in thread proc
in dummy 2
found dummy 3

Due to your obvious programming skills, it should be enough Blush | :O

.

rechi

Re: Threads and Messages

Steen Krogsgaard22-Oct-02 1:40

Steen Krogsgaard

22-Oct-02 1:40

Hmmm. The docs suggest that the message goes through the queue ("Messages sent between threads are processed only when the receiving thread executes message retrieval code."), but doesn't specify if it gets in front of the line or has to wait until the messages in front is processed. Where's Jeff Richter or Mike Blaszczak when you need them Poke tongue | ;-P

? Anyway, it's probably of little consequence.

Cheers
Steen.

"To claim that computer games influence children is ridiculous. If Pacman had influenced children born in the 80'ies we would see a lot of youngsters running around in dark rooms eating pills while listening to monotonous music"

Re: Threads and Messages

Zdenek Navratil21-Oct-02 23:06

Zdenek Navratil

21-Oct-02 23:06

I suggest an excellent article "Using Worker Threads" [^] on this subject to your attention.

Zdenek

Re: Threads and Messages

Neville Franks21-Oct-02 23:32

Neville Franks

21-Oct-02 23:32

In A as the others have said. It is not a good idea to use SendMessage between threads as you are asking for a deadlock to come knocking on your door.

Neville Franks, Author of ED for Windows. www.getsoft.com

CHtmlView

alex.barylski21-Oct-02 21:08

alex.barylski

21-Oct-02 21:08

Why does it flicker sooo much inside a CMainFrame()...?

Do I have to set the CMainFrame() to WS_CLIPCHILDREN..? Should I make sure the CMainFrame() returns false inside OnEraseBkgnd()...?

How can I get rid of the flicker...?

Thank u muchly Wink | ;)

"An expert is someone who has made all the mistakes in his or her field" - Niels Bohr

Jpeg

Kristian3321-Oct-02 20:42

Kristian33

21-Oct-02 20:42

Does anybody know some easy way to handle and
create jpeg pictures? Some free library,
or something

Regards
Janne

Re: Jpeg

Stephane Rodriguez.21-Oct-02 20:46

Stephane Rodriguez.

21-Oct-02 20:46

VS7

google.

How low can you go ?
(enculage MS)

Re: Jpeg

Christian Graus21-Oct-02 20:47

Christian Graus

21-Oct-02 20:47

ROTFL !!!!

Christian

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

During last 10 years, with invention of VB and similar programming environments, every ill-educated moron became able to develop software. - Alex E. - 12-Sept-2002

Re: Jpeg

Christian Graus21-Oct-02 20:47

Christian Graus

21-Oct-02 20:47

You mean like CXImage, FreeImage or GDI+ ? All three are documented here on CP.

Christian

Hey, at least Logo had, at it's inception, a mechanical turtle. VB has always lacked even that... - Shog9 04-09-2002

During last 10 years, with invention of VB and similar programming environments, every ill-educated moron became able to develop software. - Alex E. - 12-Sept-2002

Re: Jpeg

Daniel Turini21-Oct-02 22:04

Daniel Turini

21-Oct-02 22:04

The .NET framework has some simple methods for reading/writing jpegs. And Christian has made some awesome articles on image processing:

http://www.codeproject.com/cs/media/csharpgraphicfilters11.asp[^]

Q261186 - Computer Randomly Plays Classical Music

ASSERT in afxwin2.inl, Line 120, Please HELP!

Daniel Strigl21-Oct-02 20:23

Daniel Strigl

21-Oct-02 20:23

I have the following code:

In CMainFrame::OnCreate() function:

...
m_pCbRooms = (CComboBox*) CComboBox::FromHandle(::GetDlgItem(hBar, ID_ROOMS_COMBO));
...

I also have the following function in the CMainFrame class:

void CMainFrame::UpdateRoomList(const CMeasureData* pMeasureData, int nCurrentRoom)
{
    ASSERT_VALID(pMeasureData);
    ASSERT(nCurrentRoom >= 0 && nCurrentRoom < pMeasureData->GetRoomCount());
    ASSERT(m_pCbRooms != NULL);

    // Turn the drawing of the combo box control off

    m_pCbRooms->SetRedraw(FALSE);

    // Clear the combo box

    m_pCbRooms->ResetContent();

    // Fill the combo box control with the names of the rooms

    for (int n = 0; n < pMeasureData->GetRoomCount(); n++)
    {
        const CRoom* proom = pMeasureData->GetRoom(n);
        ASSERT(proom != NULL);
	m_pCbRooms->AddString(proom->GetDescription());
    }

    // Set the current selected string of the combo box

    m_pCbRooms->SetCurSel(nCurrentRoom);

    // Turn the drawing of the combo box control on again and redraw it

    m_pCbRooms->SetRedraw(TRUE);

    m_pCbRooms->Invalidate();
    m_pCbRooms->UpdateWindow();
}

When I call this function in the constructor of my CDocument class it works fine, but when I call this function in some CLICK-Event function, there is a ASSERTION in "afxwin2.inl" in line 120.

In the CLmsPPCDoc::OnNewRoom() event (ASSERTION):

...
((CMainFrame*) AfxGetMainWnd())->UpdateRoomList(m_pMeasureData, 0);
...

What's wrong?

Daniel Wink | ;)

---------------------------
Never change a running system!

Re: ASSERT in afxwin2.inl, Line 120, Please HELP!

Joaquín M López Muñoz21-Oct-02 20:49

Joaquín M López Muñoz

21-Oct-02 20:49

The ASSERT seems to imply that m_pCbRooms does not point to a created window when CMainFrame::UpdateRoomList is called.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

MultiDocument Interface

Anonymous21-Oct-02 18:47

Anonymous

21-Oct-02 18:47

For my MDI application Framework I normally have a Single View . i.e On a File New i get another instance of the View class .

Now I want to achieve the task of displaying two views at once. I.e when the user clicks on File--> New , user should see two view Windows . How should I do this .

All i could think of was to Add to the Document template the different views

CMultiDocTemplate* pDocTemplate;
pDocTemplate = new CMultiDocTemplate(IDR_VIEWTETYPE,
RUNTIME_CLASS(CViewTestDoc),
RUNTIME_CLASS(CChildFrame), // custom MDI child frame
RUNTIME_CLASS(CViewTestView));

AddDocTemplate(pDocTemplate);
pDocTemplate = new CMultiDocTemplate(
IDR_VIEWTETYPE,
RUNTIME_CLASS(CViewTestDoc),
RUNTIME_CLASS(CChildFrame), // custom MDI child frame
RUNTIME_CLASS(View1));

AddDocTemplate(pDocTemplate);

Now on a File New I need to show both the Views ! How to do this ? Please Help

Disable the taskbar process

suresh_sathya21-Oct-02 18:29

suresh_sathya

21-Oct-02 18:29

I am running the vc program from vbprogram using createprocess.My window
name is form1.When i click the button on the form1,i am starting my vc
program exe.Once when i start the exe,i tried to disable my vb program
taskbar name using

HWND DisWnd=FindWindow("Shell_TrayWnd","Form1");
EnableWindow(DisWnd,FALSE);

But it didnt worked out.

How to get size of maximized?

Soni21-Oct-02 17:56

Soni

21-Oct-02 17:56

When the application is started it is restored (not-maximized).
When I open the document, I want to create view of the maximised size.

How can I get the maximized size when the window is restored? Confused | :confused: