Accessing data between threads - C / C++ / MFC Discussion Boards

shiraztk13-Sep-04 22:17

13-Sep-04 22:17

Hi
I got it..it was because the specified socket was already in use in the othe machine.

Regards

The Best Relligion is Science.
Once you understand it, you will know God.

How to send user defined structure via PostMessage

ledallam13-Sep-04 21:04

ledallam

13-Sep-04 21:04

Hello,

I am trying to send a structure using PostMessage.
My structure is of the form:
typedef DATA
{
int EventID;
CString ModuleName;
CString ThreatName;
} info;

info info_data;
PostMessage(WM_MYMSG, (info_data&)wParam,NULL);

In the recieving thread I tried this way:
info_data = (info_data&)wParam; // I am getting runtime error here.

Can anyone please help me to pass a user defined structure using PotMessage?

Thanks
Madhavi

Re: How to send user defined structure via PostMessage

Arsalan Malik13-Sep-04 21:20

Arsalan Malik

13-Sep-04 21:20

Use wParam to send your structure pointer, i.e.

PostMessage(WM_MYMSG, (WPARAM)&info_data, NULL);

Note that you can only send pointer to your structure, so make sure that it is accessible in message handler.

ARSALAN MALIK

Re: How to send user defined structure via PostMessage

ledallam13-Sep-04 21:37

ledallam

13-Sep-04 21:37

Hi,

Thanks for the inputs.

When i tried this way,
AfxGetMainWnd( )->PostMessage(WM_LOGMSG, 0, (LPVOID)&info_data) ;

I got this error :
error C2664: 'CWnd::PostMessageA' : cannot convert parameter 3 from 'LPVOID' to 'LPARAM'

Can you please let me know how to proceed?

Thanks
Madhavi.

Re: How to send user defined structure via PostMessage

Arsalan Malik13-Sep-04 21:45

Arsalan Malik

13-Sep-04 21:45

Sorry for mistake. Use:

AfxGetMainWnd( )->PostMessage(WM_LOGMSG, (WPARAM)&info_data, NULL);

and in your message handler, type cast wParam to info_data pointer, i.e.

info *info_data = (info*)wParam

ARSALAN MALIK

Re: How to send user defined structure via PostMessage

Mad__13-Sep-04 23:22

Mad__

13-Sep-04 23:22

Hi,

<br />
typedef DATA<br />
{<br />
int EventID;<br />
CString ModuleName;<br />
CString ThreatName;<br />
} info;<br />
<br />
info* pinfo_data = (info*)GlobalAlloc(GPTR, sizeof(info));<br />
AfxGetMainWnd( )->PostMessage(WM_LOGMSG, 0, (LPARAM)pinfo_data);

convert to LPARAM, not to LPVOID Wink | ;)

allocate structure with API calls, and
free structure in target thread, not in main thread

Re: How to send user defined structure via PostMessage

Roger Allen14-Sep-04 12:24

Roger Allen

14-Sep-04 12:24

Dont forget also that when using PostMessage() you cannot pass pointers to objects on the stack as they may go out of scope before your message gets processed. If you need it to be done whiel its in scope, use SendMessage()

If you vote me down, my score will only get lower

Accessing data between threads

ledallam13-Sep-04 19:30

ledallam

13-Sep-04 19:30

--------------------------------------------------------------------------------

Hello,

I am writing an application which uses two threads.
I have a list<int> variable in my Document class.
THREAD 1
In this thread, I am filling a list from back i.e pDoc->list.insert(list.begin(),data);
THREAD 2
In this thread, I am extracting each element from top of the list, and displaying it on the UserInterface i.e
data = pDoc->list.pop_front();
Display(data);

THREAD1 cotinously reads and adds data at the bottom of the list while THREAD 2 gets data from the top of the list and displays it.

Can I directly access the list memeber available in my document class as above in the two threads.
When I tried the above, it worked fine when the list had limited number say 10 to 30 records, but as the size of list was growing to say 10,000 records the program was crashing.

Can anyone please help me to solve this ?

Thanks
Madhavi

Re: Accessing data between threads

Arsalan Malik13-Sep-04 19:38

Arsalan Malik

13-Sep-04 19:38

Your problem is that, you are using a shared resource (list) between two threads. You need synchronization between threads, so that only one thread at at time can access shared list. To achieve this, you can use CEvent, CMutex, or CSemaphore, depending on your needs and choice. See any good reference on these classes. Cool | :cool:

ARSALAN MALIK

Re: Accessing data between threads

Hardy_Smith13-Sep-04 21:40

Hardy_Smith

13-Sep-04 21:40

You can also try to use thread-save lists. I think there are some at www.stlport.org.
Hardy.

Handling multiple instances of an application in VC++ 6.0

Neeranjan13-Sep-04 19:07

Neeranjan

13-Sep-04 19:07

Hi,

I have an application in VC++ 6.0 and Hierarchial database files for working. Plz Note, Here I am not connecting my application to any database, insteed I am using the Hierarchial database files for my application.
1. First I start my application and open the database file using open menu which intern generates the XML files from database files. On "save" the data is saved in "Workspace"
Next time when I start the application it loads the last recently saved workspace.
2. Now I starts one more instance of same application i.e. second instance of same application. Here it loads the last saved workspace (same workspace is opened in first instance ). So working on same workspace in two different instaces is dangerous for data.

I want to restrict the second instance from loading the workspace if it is already loaded in previous instance.
Also, I should be able to work on different workspaces in different application instances.

Q: How to manage this?

Plz send any samples, codes, ideas to me
Thanx for your valuable help and support.

Thanks & Regards,
Neeraj

Re: Handling multiple instances of an application in VC++ 6.0

Arsalan Malik13-Sep-04 19:24

Arsalan Malik

13-Sep-04 19:24

Are you saving 'Workspace' as file? If yes, then while opening workspace file, open it in exclusive mode, so that access is denied to second instance of your application. For example if you are usinf CFile to open workspace use:

 CFile file;
file.Open("workspace", CFile::shareExclusive|CFile::modeReadWrite);

ARSALAN MALIK

Re: Handling multiple instances of an application in VC++ 6.0

Neeranjan13-Sep-04 19:40

Neeranjan

13-Sep-04 19:40

Thanx Malik,

I will try this and get back to you.

Thanks & Regards,
Neeraj

Re: Handling multiple instances of an application in VC++ 6.0

Anonymous14-Sep-04 0:47

Anonymous

14-Sep-04 0:47

Hi
If you want to allow only one instance of your application. You can use mutex.
Create a mutex object with specific name in initinstance. If mutex creation fails means another instance is open.

Regards,
prashant

Re: Handling multiple instances of an application in VC++ 6.0

lookforme_prash14-Sep-04 0:52

lookforme_prash

14-Sep-04 0:52

Use Mutex to restrict only one instance of application.
Create mutex with specific name in initinstance.
If function failed your application is already running

prashant

Regards,
Prashant

Re: Handling multiple instances of an application in VC++ 6.0

Neeranjan14-Sep-04 18:46

Neeranjan

14-Sep-04 18:46

Thanx prashant.

Can you send me some sample code for that?

Thanks & Regards,
Neeraj

Re: Handling multiple instances of an application in VC++ 6.0

lookforme_prash14-Sep-04 19:58

lookforme_prash

14-Sep-04 19:58

SECURITY_ATTRIBUTES secAttributes ;
secAttributes.nLength = sizeof (SECURITY_ATTRIBUTES);

CreateMutex (&secAttributes, TRUE, "PRASHANT" );
if (GetLastError () == ERROR_ALREADY_EXISTS)
{
::MessageBox (NULL, "Application is already running.", "PRASHANT", MB_OK | MB_ICONEXCLAMATION);
return 1;
}

Regards,
Prashant

Re: Handling multiple instances of an application in VC++ 6.0

Neeranjan14-Sep-04 20:16

Neeranjan

14-Sep-04 20:16

Thanx Prashant.

Where exactly I have to put this code in Initinstance?
Can you give me complete Initinstance code?

Thanks & Regards,
Neeraj

Re: Handling multiple instances of an application in VC++ 6.0

lookforme_prash14-Sep-04 20:22

lookforme_prash

14-Sep-04 20:22

It can be the first statement of initinstance

BOOL CMyApp::InitInstance()
{
SECURITY_ATTRIBUTES secAttributes ;
secAttributes.nLength = sizeof (SECURITY_ATTRIBUTES);
secAttributes.lpSecurityDescriptor = NULL ;
secAttributes.bInheritHandle = FALSE ;

CreateMutex (&secAttributes, TRUE, "prashant");

if (GetLastError () == ERROR_ALREADY_EXISTS)
{
::MessageBox (NULL, "Application already running", "Prashant",MB_ICONEXCLAMATION);
_exit(0);
}
//Rest of the code of initinstance

}

Regards,
Prashant

Re: Handling multiple instances of an application in VC++ 6.0

Neeranjan14-Sep-04 20:48

Neeranjan

14-Sep-04 20:48

Prashant thanx a lot.

It's working fine. Poping the message "Application already running" when I try to start the second instance of the application.
Still what I need is, when I click the message box "Application already running", the first instance of application should be displayed on the screen.

Thanks & Regards,
Neeraj

Win32

wow999913-Sep-04 17:40

wow9999

13-Sep-04 17:40

Hi there

How to add a toolbars to a win32 application?

Thanks

Re: Win32

PJ Arends13-Sep-04 18:21

PJ Arends

13-Sep-04 18:21

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/commctls/toolbar/toolbar.asp[^]

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Com port enable

anuchelvi13-Sep-04 17:10

anuchelvi

13-Sep-04 17:10

hi,
my module is to enable the comports which r present in the system.
For eg: if COM port1 & 3 r present in my system, then 1 & 3 should be enabled in my menu bar.
void CComDlg::OnUpdateport2(CCmdUI* pCmdUI)
{
// TODO: Add your command update UI handler code here
if(port3==1)
pCmdUI->Enable(TRUE);
else
pCmdUI->Enable(FALSE);

Is this the correct method to enable the port which is present in the system?
But it is not working.
Pls help.
Mithila

mithila

Re: Com port enable in menu bar

anuchelvi13-Sep-04 21:12

anuchelvi

13-Sep-04 21:12

hi,
pls help any one.

mithila

Re: Com port enable in menu bar

shiraztk13-Sep-04 21:31

shiraztk

13-Sep-04 21:31

Hi,

What I understand from your question is that you want to work with com ports, right ? then, I think you should use GetCommState and SetCommState api after fillig in the DCB.

Regards
Shiraz

The Best Relligion is Science.
Once you understand it, you will know God.

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