C / C++ / MFC

zecodela11-Nov-02 19:28

zecodela

11-Nov-02 19:28

actually, i read some articles on multithread programming.
i know it need to use CriticalSection, Mutex to protect data member from being accessed by more than a thread per times.
however, i don't so sure the problem on member functions.
u have mentioned about one copy of stack per thread. what will it affect when thread access a member function?

thanks,
jim

Joao Vaz11-Nov-02 22:12

Joao Vaz

11-Nov-02 22:12

For instance Thread A calls func that modifies array x, that is a normal instance member variable of the class Xpto.

x[i++]=dumbValue;

Thread B calls func that modifies array x
x[i++]=dumbValue;

Another thread or other function or ... reads the value
y=x[i];

What is the value, the value added by thread A, or thread ?

If you count on a specific order , you could get in trouble with this, in this case you must protect array x to be thread safe and to serialize access, to maintain data in a coerent and expected state , get it ?

Cheers,Joao Vaz
And if your dream is to care for your family, to put food on the table, to provide them with an education and a good home, then maybe suffering through an endless, pointless, boring job will seem to have purpose. And you will realize how even a rock can change the world, simply by remaining obstinately stationary.-Shog9

Remember just because a good thing comes to an end, doesn't mean that the next one can't be better.-Chris Meech

Anonymous12-Nov-02 0:41

12-Nov-02 0:41

you are talking about kind of global or class member variable.
but, what will happen for local variable inside a function?
used my example, here is the implementation of commonfunction() in my question

void commonfunction()
{
for(int i=0; i<100;i++)
{
i= i+i;
}
printf("%d", i);
}
if both thread A and B access commonfunction()
will local variable, 'i' corrupt?

thanks,
jim

my ado program don't work on another pc?

Joao Vaz12-Nov-02 1:58

Joao Vaz

12-Nov-02 1:58

Anonymous wrote:
if both thread A and B access commonfunction()
will local variable, 'i' corrupt?

No, because as I said, each thread has their own stack, so each thread have independent copies of the local variables Smile | :)

So, the loop is performed two times independently by the two threads.
This function is also reentrant, because it don't use static neither global variables.
Resumming , no problems at all if you only use local variales Smile | :)

HTH

Cheers,Joao Vaz
And if your dream is to care for your family, to put food on the table, to provide them with an education and a good home, then maybe suffering through an endless, pointless, boring job will seem to have purpose. And you will realize how even a rock can change the world, simply by remaining obstinately stationary.-Shog9

Remember just because a good thing comes to an end, doesn't mean that the next one can't be better.-Chris Meech

sages11-Nov-02 16:03

sages

11-Nov-02 16:03

I have done a db program.Using ado to access oracle806 db,I used Oracle OleDB provider to improve performance.
It's fine on my pcs(xp/98,oracle 817 client) .However ,
After release it(using vc++6.0 install shield),it does not work on some pcs.It seem program do not connect to oracle.
On others,it work well.Try connecting the oracle with SQL*PLUS,i find the net8 is ok.What's wrong with my program? I suppose the program is Oracle OleDB provider.
Help me ,please.

Re: my ado program don't work on another pc?

Christian Graus11-Nov-02 17:17

Christian Graus

11-Nov-02 17:17

sages wrote:
,I used Oracle OleDB provider to improve performance.

The Microsoft one is slower, but it doesn't leak memory. If you tie yourself to it now, you'll have a slower, but more reliable database.

sages wrote:
I suppose the program is Oracle OleDB provider.

Probably, yes. Be careful though - every Oracle patch comes with the full Oracle installation program, and running a patch could mean you can not ever remove Oracle using an uninstaller, plus it's almost certain that the Oracle Enterprise Manager will stop working on the machine in question. The same is true if you do an MDAC upgrade, but 2.7 does fix the memory leak I mentioned earlier ( at the expense of never being able to run the Enterprise Manager again ).

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

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

Thanks,i've resolved th problem.

sages11-Nov-02 20:11

sages

11-Nov-02 20:11

The Oracle OLEDB provider has been changed to MS OLEDB provider.It's OK.Thanks you for your help.good luck to u.
Wink | ;)

Wizard goes Next in Windows 98

Swinefeaster11-Nov-02 14:13

disable individual rows of a listctrl

11-Nov-02 14:13

Hyello,

I have a Wizard in my application which works flawlessly on Windows 2000/Xp, but under Windows 98, I get some weird stuff going on. On some pages, when you hit the Next button, it advances either back to the beginning, or some other page other than the next one --- though it does work sometimes.

Has any run into this problem? I've been trying to trace the problem through in Windows 98, but the whole os tends to lock up and it's really frustrating! WTF | :WTF:

Thanks!

swine

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fordge11-Nov-02 13:55

fordge

11-Nov-02 13:55

can anyone tell me how i can disable selection of individual rows of a listctrl.
if u suggest ODS_DISABLED
please elaborate
cause i cant get it to work properly..

Swinefeaster11-Nov-02 14:08

11-Nov-02 14:08

i believe you have to implement this yourself Frown | :(

swine

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fordge11-Nov-02 20:37

fordge

11-Nov-02 20:37

do u remember the vstudio 6 help
the msdn then had the index and u could filter the list box accoring to language like for vc vb ...etc..and according to the filter all the contents not in that language would be disabled(grayed out)..
thats the kind of thing im talking off..

do umean to say that that not possible standardly and has to be implemented seperately??

Swinefeaster11-Nov-02 20:40

11-Nov-02 20:40

yep, as far as i know. it's not that hard to do though... there's a bunch of articles on how to do stuff like this here in codeproject. you could also do a search for CListCtrl::DrawItem().

cheers,

swine

Check out Aephid Photokeeper, the powerful digital
photo album solution at www.aephid.com.

Michael Dunn11-Nov-02 16:55

Michael Dunn

11-Nov-02 16:55

Handle LVN_ITEMCHANGING. Examine the iItem and uNewState members of the struct you are passed, and if an item is becoming selected, and you don't want it to be, return TRUE from the handler to prevent the change.

--Mike--
"alyson hannigan is so cute it's crazy" -- Googlism
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Anonymous11-Nov-02 20:38

CLabel control with property sheet question

11-Nov-02 20:38

please elaborate if possible
a code snipet would be helpful

Cannot figure it out

ed987111-Nov-02 13:01

ed9871

11-Nov-02 13:01

I have never gotten an error in release mode that I did not get in debug mode. In CView::OnFilePrint() somewhere between OnBeginPrinting and OnPrepareDC (the two functions I can override and put some message boxes in so I can see where I am while in release mode) I am getting this:

Unhandled exception at 0x0050f277 in Paradigm.exe: 0xC0000005: Access violation reading location 0x00000002.

I have exhausted my knowledge trying to figure out why this is happening.

I can set a breakpoint for this address and it hits it three other times during execution before it bombs in OnFilePrint(). VS says there is no source code associated with this address. The dissassembly is as follows:

0050F277 66 81 7B 02 FF FF cmp word ptr [ebx+2],0FFFFh

Where do I go from here? I'm sure there are things to do that are outside my knowledge base. It works perfectly in debug mode.

Ed

Re: Cannot figure it out

Christian Graus11-Nov-02 17:19

Christian Graus

11-Nov-02 17:19

There is a good article here on CP about how to fool the debug version into thinking it's a release version, so you can catch these errors in the debugger.

Christian

No offense, but I don't really want to encourage the creation of another VB developer. - Larry Antram 22 Oct 2002

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

DalTXColtsFan11-Nov-02 12:53

DalTXColtsFan

11-Nov-02 12:53

Greetings all,

I have a question. I'm using Norm Almond's CLabel control on a Property Page. I want to allow the user to select some colors and then have a rectangle on the dialog with the color the user chose. It was working perfectly as a CDialog.

What's happening now is I'm trying to make that dialog a PropertyPage as part of a PropertySheet. Here are the changes I made to InitInstance:

BOOL CPropertySheetDemoApp::InitInstance()
{
// Standard initialization
// If you are not using these features and wish to reduce the size
// of your final executable, you should remove from the following
// the specific initialization routines you do not need.

/*CPropertySheetDemoDlg dlg;
m_pMainWnd = &dlg;
int nResponse = dlg.DoModal();
if (nResponse == IDOK)
{
// TODO: Place code here to handle when the dialog is
// dismissed with OK
}
else if (nResponse == IDCANCEL)
{
// TODO: Place code here to handle when the dialog is
// dismissed with Cancel
}*/

CPropertySheet mySheet;
CMyPropertyPage myDemoPage;
myDemoPage.m_lblTest.SetBkColor(RGB(1.0, 1.0, 1.0));
mySheet.AddPage(&myDemoPage);

mySheet.DoModal();

// Since the dialog has been closed, return FALSE so that we exit the
// application, rather than start the application's message pump.
return FALSE;
}

As you can see I just commented out the stuff to bring up the initial dialog and am trying to bring up the property sheet instead. The error I'm getting is a debug assertion failure in the UpdateSurface() method of the CLabel class. It seems to be complaining that the window hasn't been drawn or doesn't have an hWnd yet.

Any suggestions? I just want to be able to initialize the colors on the labels as they come up, and they may not always be the same colors.

I'd appreciate any suggestions!

Joe

CSocket::Receive (from more than one computer)

Walote11-Nov-02 10:47

Walote

11-Nov-02 10:47

Hi!!

I have a connection between two computers, that work's OK. Command NETSTAT show the ESTABLISHED status under this connection, but I need to receive from a third computer. On the 3rd computer, the NETSTAT command show the ESTABLISHED status too, but the CSocket::Receive from the server, can not listen from there...

what was wrong?

Thank's.... Walote

CString from a UI Thread

Anonymous11-Nov-02 10:25

11-Nov-02 10:25

Hello,
I have a UI thread and I do a PostMessage from the thread to the application with the lParam set as a CString.. in my receiving function i do a

LRESULT CMainFrame::OnMarkOffLine(WPARAM wParam, LPARAM lParam)
{
	CString* name = (CString*)lParam;
	CString strName = *name;
..SNIP........

but i am getting a access violation here...

CString::CString(const CString& stringSrc)
{
	ASSERT(stringSrc.GetData()->nRefs != 0); <-Here
	if (stringSrc.GetData()->nRefs >= 0)
	{
		ASSERT(stringSrc.GetData() != _afxDataNil);
		m_pchData = stringSrc.m_pchData;
		InterlockedIncrement(&GetData()->nRefs);
	}
	else
	{
		Init();
		*this = stringSrc.m_pchData;
	}
}

What am I doing wrong??

dabs11-Nov-02 10:39

dabs

11-Nov-02 10:39

There is nothing inherently wrong with the code you posted (although I would recommend that you replace the C-style typecast with a more appropriate C++ typecast but that's another matter altogether). Show us the code that sends (or posts) this message.

Wenn ist das Nunstück git und Slotermeyer? Ja! Beierhund das oder die Flipperwaldt gersput!

Anonymous11-Nov-02 10:45

This seemed to fix it.. weird

11-Nov-02 10:45

Here's the PostMessage

PostMessage(this->GetMainWnd()->GetSafeHwnd(),UWM_OFFLINE,0,(LPARAM)&m_strDns);

Anonymous11-Nov-02 10:59

11-Nov-02 10:59

CString name = (LPCSTR)lParam;

instead of the

CString* name = (CString*)lParam

Re: Its not fixed

Anonymous11-Nov-02 11:26

11-Nov-02 11:26

Actually the error went away but the string contains garbage..

Dead | X|

Swinefeaster11-Nov-02 14:07

11-Nov-02 14:07

I know exactly what your problem is! Smile | :)

You can't use pointers to objects with a PostMessage(), because PostMessage() does not hang the calling thread and wait until the receiving thread processes the message, unlike SendMessage(). What happens is that the CString object in your calling thread gets destroyed before the receiving thread gets a chance to access the strings contents.

The solution to this is kind of a pain. You need to create a central map / list container that holds a bunch of strings, and then pass handles (or even pointers) to those strings in your messages. Then you delete the string once you receive the message, or perhaps after some time.

Hope this helps!

swine

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