Need help resolving a deadlock - C / C++ / MFC Discussion Boards

Gary R. Wheeler4-Jun-05 3:21

4-Jun-05 3:21

Rather than validating on the EN_CHANGE notification, try using the EN_KILLFOCUS notification. With EN_CHANGE, your user will get very frustrated trying to enter a valid value. Every keypress, you will try and validate what they are entering. With EN_KILLFOCUS, you validate only when they leave the control (which implies they are ready to commit the value).

Software Zen: delete this;

Re: Stack Overflow on Edit Box

Gary R. Wheeler4-Jun-05 3:36

Gary R. Wheeler

4-Jun-05 3:36

Something else: You don't need to call m_strEditValue.GetBuffer() in your atof() function call. Just pass m_strEditValue, and the built in cast to a LPCTSTR will take care of the required conversion.

Something else #2: In other circumstances, if you have to use GetBuffer() with a CString value, make sure you call ReleaseBuffer(). This ensures that the CString manages the buffer memory correctly.

Software Zen: delete this;

Re: Stack Overflow on Edit Box

Grahamfff4-Jun-05 8:24

Grahamfff

4-Jun-05 8:24

Thanks will use OnKillFocus, works better that way.

Graham.

grahamfff

Getting a window that uses directdraw?

Programmer_4_L1f33-Jun-05 11:07

Programmer_4_L1f3

3-Jun-05 11:07

I tried several times to get Diablo 2's window, came up with nothing... all I need is some insite on what to do. I image it would be the same for putting a label inside it, as it is in regular windows. Am I right? If perhaps, you need more info. then please let me know, by replying...

Thanks for replying, when you do!
Programmer_4_Fu73r

Re: Getting a window that uses directdraw?

Azrael.LingChen3-Jun-05 20:23

Azrael.LingChen

3-Jun-05 20:23

I am studying to use the DirectDraw, have what can I help?

I come from China, is a plait distance raw recruit.My English level is badly.

Graying Out Tabs in a Property Page

laiju3-Jun-05 10:38

laiju

3-Jun-05 10:38

I have a property page with 4 tabs. How do I gray out a particular tab at run time.
Similarly my application (generated from MDI Doc -View Architecture) has
the SAVE icon.
This icon is enabled throught the application.I want it to be enabled only when changes are done to my application.How do i do this.
Any suggestions please.

Thanx in advance

laiju

Re: Graying Out Tabs in a Property Page

David Crow3-Jun-05 11:03

David Crow

3-Jun-05 11:03

See here.

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

Need help resolving a deadlock

Budric B.3-Jun-05 10:19

Budric B.

3-Jun-05 10:19

Hi,
I have 2 threads that for some reason lock up and I can't figure out why. Maybe if someone could look at some of my code they can see something obviously wrong:

<br />
UINT CChildView::CaptureThread()<br />
{<br />
	bool ShutterChanged = false;<br />
	int saveShutter;<br />
	while(!m_bTerminateThread)<br />
	{<br />
		//wait<br />
		if (m_bCapturePaused)<br />
		{<br />
			::SetEvent(m_hCapturePausedConfirm);<br />
			switch(::WaitForSingleObject(m_hCaptureEvent, 5000))<br />
			{<br />
				case WAIT_OBJECT_0:<br />
					break;                //break out of the switch statement<br />
				case WAIT_TIMEOUT:<br />
					continue;             //continue with the switch statement<br />
			}<br />
		}<br />
...rest of the thread<br />
Note that inside this thread I use an object which implements CCriticalSection object that I lock and unlock for each function.  Both the GUI thread and this thread calls functions on this object.<br />
}<br />
Furthermore I define:<br />
	inline void StartCapture()<br />
	{<br />
		m_bCapturePaused = FALSE;<br />
		::SetEvent(m_hCaptureEvent);<br />
		::ResetEvent(m_hCapturePausedConfirm);<br />
	}<br />
	inline void PauseCapture()<br />
	{<br />
		m_bCapturePaused = TRUE;<br />
		::ResetEvent(m_hCaptureEvent);<br />
		::WaitForSingleObject(m_hCapturePausedConfirm, INFINITE);<br />
	}<br />

The problem is in the main program when the user clicks a button I want to pause the thread. The deadlock doesn't occur always. Also any runs through the debugger work, so I don't know how to solve this problem.

Thanks.

Re: Just found the problem

Budric B.3-Jun-05 11:02

Budric B.

3-Jun-05 11:02

First, I finally found how to debug multiple threads in VC++ 6. Run in debug mode, click pause, click Debug->Threads. After I did that I immediately saw the thread executing a line CComboBox::GetCurSel(). I thought I didn't have any more GUI modification within a thread but I guess I do. I think the problem is now fixed. I guess people aren't kidding when they say don't modify the GUI from a thread.

Re: Just found the problem

Blake Miller3-Jun-05 11:08

Blake Miller

3-Jun-05 11:08

I guess people aren't kidding when they say don't modify the GUI from a thread.

Don't modify the MFC GUI from a thread that did not create the MFC object - you can modify any of them from the same thread that created them, of course.

A question about CBT hook

Gaetano Sferra3-Jun-05 9:10

Gaetano Sferra

3-Jun-05 9:10

I need to develop a little application to send some keystrokes to the active window, something like the On Screen Keyboard. I need to know what is the window that lose the keyboard focus when the user click on a button in my application so I tried to gain a hook (a thread hook, not a global hook) so I wrote the following routine as CBT event handler:

<br />
LRESULT CALLBACK<br />
CMainFrame::CBTProc(int nCode, WPARAM wParam, LPARAM lParam)<br />
{<br />
  LRESULT nResult;<br />
<br />
  if (nCode == HCBT_SETFOCUS)<br />
  {<br />
    m_hGaining = (HWND) wParam;<br />
    m_hLosing = (HWND) lParam;<br />
<br />
    TRACE1("HWND Gaining: %x\n", m_hGainingFocusWnd);<br />
    TRACE1("HWND Losing: %x\n", m_hLosingFocusWnd);<br />
  }<br />
<br />
  nResult = CallNextHookEx(m_hHook, nCode, wParam, lParam);<br />
<br />
  return nResult;<br />
}<br />

The problem is that when I switch (using mouse or Alt+Tab) between my application and another one such as Notepad I got this behaviour:

Switching from Notepad to my application:
HWND Gaining: 0x50558 (the handle of my application window)
HWND Losing: 0 (NULL) Confused | :confused:

Switching from my application to Notepad:
the hook procedure don't trap anything at all Confused | :confused:

What's wrong? Why I get NULL in the first case and I don't trap nothing in the second one?

Thanks

Gaetano Sferra

Re: A question about CBT hook

Nilesh K.5-Jun-05 23:32

Nilesh K.

5-Jun-05 23:32

In a call to SetWindowsHookEx(), set the last parameter as '0' This would associate hook with all the existing threads.

<bold>- Nilesh
<italics>
"Reading made Don Quixote a gentleman. Believing what he read made him mad" -George Bernard Shaw

Re: A question about CBT hook

Gaetano Sferra6-Jun-05 0:44

Gaetano Sferra

6-Jun-05 0:44

Nilesh K. wrote:
In a call to SetWindowsHookEx(), set the last parameter as '0' This would associate hook with all the existing threads.

Looking into the MSDN, in the SetWindowsHookEx explaination I see the following:

lpfn
[in] Pointer to the hook procedure. If the dwThreadId parameter is zero or specifies the identifier of a thread created by a different process, the lpfn parameter must point to a hook procedure in a dynamic-link library (DLL). Otherwise, lpfn can point to a hook procedure in the code associated with the current process.

If I set the last parameter of the SetWindowsHookEx() (dwThradId) to 0 I cannot provide a pointer to an hook procedure that reside in the my application process as shown in my previous post, I shoud build a DLL.

My questions are:
Can I obtain a handle to the window losing the keyboard focus without use a global hook (a hook procedure in a DLL)?

Why when my application window lose the ketyboard focus the hook procedure isn't called? (It should trap a CBT event with the lParam set to the handle to my application window)

Why when my application window gain the keyboard focus I got NULL as handle to the window losing the keyboard focus? (I should get the correct handle because the CBT event destination is the my application process)

If my interpretation of MSDN or my deductions are wrong, please correct me.
Thanks

Gaetano Sferra

Re: A question about CBT hook

Nilesh K.6-Jun-05 16:43

Nilesh K.

6-Jun-05 16:43

I doubt it would be possible without global hook procedure.

<bold>- Nilesh
<italics>
"Reading made Don Quixote a gentleman. Believing what he read made him mad" -George Bernard Shaw

Re: A question about CBT hook

Gaetano Sferra6-Jun-05 21:23

Gaetano Sferra

6-Jun-05 21:23

Thank you Nilesh,
I will begin a DLL development to handle it.

Gaetano Sferra

Need help converting this inline asm cosf function for use in a gnu compiler

FocusedWolf3-Jun-05 8:36

FocusedWolf

3-Jun-05 8:36

inline float FastCosF(float value)<br />
{<br />
#ifdef Im_In_VisualStudio<br />
<br />
	__asm<br />
	{<br />
		fld value;<br />
		fcos;<br />
		fstp value;<br />
	}<br />
<br />
#else //in GNU compiler<br />
<br />
        //hmm<br />
<br />
#endif<br />
<br />
	return value;<br />
}<br />

Through googling i got this: asm ("fsin" : "=t" (value) : "0" (value));

but i don't think it works

Re: Need help converting this inline asm cosf function for use in a gnu compiler

C^hris L^osinger3-Jun-05 8:54

C^hris L^osinger

3-Jun-05 8:54

which CPU are you targeting?

i think the author of that bit is assuming anyone using Visual Studio compiler is going to be making EXEs for use on Pentium (and compatible) processors. but since gcc is used on many different architectures, not just Pentiums, you can't make the same assumption - and you'll have to pick a processor(s) to write for.

Cleek | Image Toolkits | Thumbnail maker

Re: Need help converting this inline asm cosf function for use in a gnu compiler

FocusedWolf3-Jun-05 11:08

FocusedWolf

3-Jun-05 11:08

Hmm i didn't consider that...shows how much i know about asm. Looks like for sake of multiplatform im just gonna have to use the built in math functions.

How to know whether a device is connected to my USB port or not

anukampa3-Jun-05 4:58

anukampa

3-Jun-05 4:58

Please help me in writing a code to know whether a webcam is attached to any USB port or not? This is very urgent

Thanking you
anukampa

Re: How to know whether a device is connected to my USB port or not

Trollslayer3-Jun-05 13:14

Trollslayer

3-Jun-05 13:14

The easiest way would probably be to use the driver for that device to check it's status.

Elaine Rose | [Rose]

The tigress is here Big Grin | :-D

Re: How to know whether a device is connected to my USB port or not

FlyingTinman3-Jun-05 14:36

FlyingTinman

3-Jun-05 14:36

If the webcam has a valid driver installed you just
need to enumerate connected video devices and look
for a "friendlyname" that matches that of your webcam.

Look at AMCAP source code (in the DirectShow SDK samples)
for details of how to do that. AMCAP enumerates all
connected video devices and lists their "friendlyname"s
in a menu from which the user can select one.

Steve T

CComboBox selection state before CBN_SELCHANGE

stevy823-Jun-05 4:24

stevy82

3-Jun-05 4:24

I need to know the Combobox selection that was before the user changed the selection.
If I use

OnChangeCbXXX() {<br />
     int selection = m_cbXXX.GetCurSel()<br />
}

then selection holds the new value. How to get the value before the change???

Re: CComboBox selection state before CBN_SELCHANGE

David Crow3-Jun-05 5:28

David Crow

3-Jun-05 5:28

Just create another member variable that defaults to -1. On the CBN_SELCHANGE handler, do something like:

OnChangeCbXXX()
{
    int selection = m_cbXXX.GetCurSel();
 
    TRACE("Previous selection = %d\n", m_prevsel);
    TRACE(" Current selection = %d\n", selection);
    
    m_prevsel = selection;
}

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

Monitoring opened files

0908869039@seznam.cz3-Jun-05 3:37

0908869039@seznam.cz

3-Jun-05 3:37

How can I find out opened files on LAN ? I would like to use it in my app. I mean this Computer management->System tools->Shared folders->Open files

Re: Monitoring opened files

David Crow3-Jun-05 4:03

David Crow

3-Jun-05 4:03

See here and here for possibilities.

"Ideas are a dime a dozen. People who put them into action are priceless." - Unknown

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.