C / C++ / MFC

Re: How to access a single object from multiple thread

27-Jan-08 21:57

Hello friends

I am using VC++ 6.0 for writing a multi threaded application. But I am facing problems when I try to Update a recordset (CRecordset object) from multiple threads running simultaneously
please help

Ranojay

Iain Clarke, Warrior Programmer27-Jan-08 22:02

Re: How to access a single object from multiple thread

27-Jan-08 22:02

Have a look at critical sections - they could be your friend.

CreateCriticalSection<br />
EnterCriticalSection<br />
LeaveCriticalSection<br />
DestroyCriticalSection

(? - could be delete)

Good luck,

Iain.

Ranojay28-Jan-08 20:20

Re: How to access a single object from multiple thread

28-Jan-08 20:20

Thank you Sir for your help

But the functions

EnterCriticalSection<br />
LeaveCriticalSection<br />

are giving error messages while in use

can you be more specific about how to use them

thanks again

Iain Clarke, Warrior Programmer28-Jan-08 21:50

Re: How to access a single object from multiple thread

28-Jan-08 21:50

I have *never* had one of those functions giving me an error. The only thing I can think of is that you've not initialised the critical section before using it. Look on
MSDN for EnterCriticalSection. One of the links take you to an example page for critical sections. (Copied below)

I would avoid the use of a global variable, and make the critical section a co-member of a class with your recordset, but I hope you'll get the idea.

Iain.

// Global variable
CRITICAL_SECTION CriticalSection; 

void main()
{
    ...

    // Initialize the critical section one time only.
    InitializeCriticalSection(&CriticalSection); 

    ...

    // Release resources used by the critical section object.
    DeleteCriticalSection(&CriticalSection)
}

DWORD WINAPI ThreadProc( LPVOID lpParameter )
{
    ...

    // Request ownership of the critical section.
    __try 
    {
        EnterCriticalSection(&CriticalSection); 

        // Access the shared resource.
    }
    __finally 
    {
        // Release ownership of the critical section.
        LeaveCriticalSection(&CriticalSection);
    }

    ...

}

Ranojay30-Jan-08 20:49

Re: How to access a single object from multiple thread

30-Jan-08 20:49

Thanks again

I will try that. Actaully I am using the CWinThread Run() function from a CWinThread derived class

and doing the simultaneous update of the CRecordSet object and not AfxBeginthread function

will that work too?

anyway thank you very much for your help
and I will keep you disturbing
Thanks a lot

Iain Clarke, Warrior Programmer30-Jan-08 21:57

Re: How to access a single object from multiple thread

30-Jan-08 21:57

The code I showed was just an example - mostly for initialising the critical section.

Any code wrapped up by a Enter/LeaveCriticalSection pair will be callable from only one thread at a time. This includes any calls you make to a database, etc. It doesn't matter whether you make a thread using CWinThread::Run, AfxBeginThread, or ::CreateThread (mostly because they all end up being a call to BeginThread).

Iain.

Ranojay1-Feb-08 22:03

Network detection on windows 98

1-Feb-08 22:03

Sir
I tried all the functions but it is still not working
some rows are surely getting updated but some of them are not
the error Mesage is No rows were affected by the update or delete operation.

has it any thing to do with the type of database I am using.Actually I am uising MS-ACCESS database.

may be ACCESS is not able to handle concurrent updates

Somnath_Mali27-Jan-08 20:36

Somnath_Mali

27-Jan-08 20:36

Hi,

in my application I need to check if network is available. I have used the function InternetGetConnectedState.

But this function is not working on Windows 98. It always returns "Network connected State".

Is any other way, to check the network ( INTERNET ) connection on 98.

Regards

Somnath

Re: Network detection on windows 98

David Crow28-Jan-08 5:11

David Crow

28-Jan-08 5:11

Somnath_Mali wrote:
It always returns "Network connected State".

And is that not right?

Have you tried IsNetworkAlive() or InternetCheckConnection()?

"Show Desktop" windows event?

Somnath_Mali27-Jan-08 20:31

Somnath_Mali

27-Jan-08 20:31

Hi,

We have windows application, which should track if Desktop window is active and process some code if desktop is active.

Is any way to track the events which gets called when user selects "show desktop" from Quick launch OR "show desktop" from right click on task bar OR window+D.

Regards,
Somnath

Re: "Show Desktop" windows event?

David Crow28-Jan-08 5:13

David Crow

28-Jan-08 5:13

Have you used Spy++ to see what message(s) your application receives when all top-level windows are minimized?

help [modified]

gentleguy27-Jan-08 20:24

27-Jan-08 20:24

dear all

how to solve the following problem: thanks

actually the problem is from this line:

vn[ii][j][k] = w*v[ii][j][k] + c1*rand()*(pbestArray[ii][j][k]-x[ii][j][k]) + c2*rand()*(gbest[j][k]-x[ii][j][k]);

xn[ii][j][k] = x[ii][j][k] + v[ii][j][k] + (a1*(g-fitness(ii)));

TestSource.cpp(258) : error C2064: term does not evaluate to a function

thanks..after compilation, the errer is above..

Li Zhiyuan

5/10/2006

modified on Monday, January 28, 2008 2:30:03 AM

Iain Clarke, Warrior Programmer27-Jan-08 21:49

27-Jan-08 21:49

1/ Please read the guidelines - it's attached to the top of the forum, and in big letters tells you to use a meaningful topic.

I've yet to see someone post a message, but say "please don't help me".

2/ You show an error on a line of code, then show TWO lines of code. Which one is wrong?

3/ You can solve the problem yourself.

Start with
vn[ii][j][k] = 1; does that compile happily?
vn[ii][j][k] = w*v[ii][j][k]; does that compile happily?
vn[ii][j][k] = w*v[ii][j][k] + c1; does that compile happily?
vn[ii][j][k] = w*v[ii][j][k] + c1*rand(); does that compile happily?

I'm bored now, but I hope you get the idea.

Or you can read the error message. To call a function, you use ()'s. So, look for () that should not be there, or be [] as an array variable.

Good luck,

Iain.

CPallini27-Jan-08 23:26

27-Jan-08 23:26

If I recall well from you previous posts, fitness is an array, hence you need to access its elements via [] operator. Probably you have to replace fitness(ii) with fitness[ii].
BTW I suggust you to read some introductory documentation on C/C++ programming.
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

gentleguy27-Jan-08 23:55

27-Jan-08 23:55

thanks, brother, solved already,i still has a problem:

LINK : fatal error LNK1104: cannot open file "psoCode.lib"
Error executing link.exe.

psoCode.lib is static library what i created..i really tried many manners to solve it..anyone can provide me with own email, i can pass my source code to you and you help me to solve it, thanks a lot.size of file is so small.....thanks again..my email address is lizhiyuan16@hotmail.com.

i compiled static library and main function file respectively, but it is no problem..and after dependency...this problem occurred...

Li Zhiyuan

5/10/2006

CPallini28-Jan-08 0:23

28-Jan-08 0:23

There's no need to send code, you simply need to make Visual Studio know about your library file psoCode.lib folder path. You have to add that folder path to the Library files directory list, I already posted you about
(alternatively, quick and dirty method, you can put your library file psoCode.lib inside a Visual Studio well known path, for instance the lib subfolder of the Visual Studio installation one).
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

gentleguy28-Jan-08 13:31

28-Jan-08 13:31

dear friend

could you give me some detail, for example: first step..second...let me check carefully..but actually i already set all requirement what program demand....

thanks a lot..

Li Zhiyuan

5/10/2006

CPallini28-Jan-08 21:16

28-Jan-08 21:16

I've Visual Studio 2005, but I think it applies also to VS2003 & VS2008:
(1) Find you library folder path, i.e. the path of the folder containing the file psoCode.lib.
(2) On Visual Studio, select Tools->Options menu item.
(3) On the newly appeared window, select the Projects and Solutions->VC++ Directories node.
(4) Select Library files item in the Show directories for listbox.
(5) Add the folder you found at point (1) to the list of library folders, you can use the browse button.

Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

[my articles]

gentleguy28-Jan-08 23:30

28-Jan-08 23:30

but i use vc++6.0..so far..how to set? is this same way? thanks....

Li Zhiyuan

5/10/2006

CPallini28-Jan-08 23:42