Re: Multithread problem with DLL - C / C++ / MFC Discussion Boards

geo_m3-Feb-05 9:51

3-Feb-05 9:51

This is not about multithreaded dll - this is how the windows handles the dll libraries - it is loaded only once in the memory for saving resources. When you call subsequent LoadLibrary it simply increments the usage counter.

If you LoadLibrary from other process, it is a different story. There are some nifty stuff inside the windows, but for you it's like the dll is loaded again --> you can load your library only once into process memory.

Difference between library compiled as multithreaded or singlethreaded is AFAIK only difference with c runtime support libraries used. If you will not use functions like printf etc, there is no difference between dll compiled as multithreaded or singlethreaded.

There's no way, how to determine, if the dll was compiled as multithreaded, neither way how to change it (without having sources and recompile).

But for your problem as you described, it makes no difference I guess.

Re: Multithread problem with DLL

Rick York3-Feb-05 11:51

Rick York

3-Feb-05 11:51

There are quite a few run-time library functions that have global/static variables whose storage specification changes for the multithreaded versions. The multithreaded versions use the __declspec( thread ) keywords to specify thread-local storage for those variables which means that each thread gets its own copies of each variable.

Re: Multithread problem with DLL

geo_m3-Feb-05 19:21

geo_m

3-Feb-05 19:21

Thank you. Didn't know it. Or better didn't think about Cool | :cool:

I just got it as - I don't know which functions have some global/static parts and I don't know if it can or cannot change. Therefore I decided to took the run-time library as a block - either use it, but then compile carefully with appropriate switch or dump it completely.

Re: Multithread problem with DLL

djavanci4-Feb-05 0:25

djavanci

4-Feb-05 0:25

I'm not using LoadLibrary method.
I'm importing the .tlb of the DLL file and then linking to my program.
To create a new instance of the DLL, im using the methods CoInitializeEx with the parameters 0 and COINIT_MULTITHREADED and then CoCreateInstance with the parameters CLSID_DLL, NULL, CLSCTX_ALL, IID_IUnknown, (LPVOID*)&pointer);

Re: Multithread problem with DLL

geo_m4-Feb-05 4:13

geo_m

4-Feb-05 4:13

CoCreateInstance does some COM dancing around and then calls LoadLibrary for you.

Re: Multithread problem with DLL

Christopher Lloyd3-Feb-05 12:10

Christopher Lloyd

3-Feb-05 12:10

It sounds to me like your problem is with global variables in the DLL - i.e. there's only one variable X but when you run two threads they'll both be able to change it. Same thing applies to any static variables in functions.

If this is the problem then it implies that the DLL's author wasn't expecting the DLL to be run in different threads in which case it assumedly wasn't linked with the Multithreaded runtime libraries which will create a different set of issues.

A solution is not too easy. You could:
1. Use thread local storage (see "Using Thread Local Storage in a Dynamic-Link Library" in the SDK documentation) to sort out the variables (or use __declspec(thread) which might be easier). However, you will need to understand which variables should and which shouldn't be accessable to all threads.
2. Re-build using the mutli-threaded libraries.

However, You might still have issues with any resources the DLL uses (such as intentionally shared variables). To sort this out you'd need to use some type of synchronisation object such as a mutex (or create a critical section) to control multi-threaded access. There's lots of stuff about this in the SDK.

Depending what the DLLs actually does, it might be easier to rewite it yourself or look for an alternative.

Re: Multithread problem with DLL

djavanci4-Feb-05 1:02

djavanci

4-Feb-05 1:02

About the item 1, I will analyze further the method __declspec(thread) and try to use it.
But in the 2nd item, you told me to rebuild DLL using the multi-threaded libraries. In Visual C++ 6, Project->Settings, C/C++ tab with Code Generation option selected, it has an combo box called "Use run-time library". The option selected there already is "Multithreaded DLL". There's another way to configure this? How it does?

Dennis

Re: Multithread problem with DLL

Christopher Lloyd4-Feb-05 2:51

Christopher Lloyd

4-Feb-05 2:51

I was only assuming that the DLL was built without the Multithreaded option on because you said you were getting these problems. If the option's already set then that's fine.

By the way __declspec(thread) isn't a method. It's a storage class modifier. For example if you want to define a static variable in a function then you would use:

__declspec(thread) static int MyVar;

You'll find more about this here: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclang/html/_pluslang_the_thread_attribute.asp[^]

creating dynamic menus in dialog based apllications

ganapathykumar3-Feb-05 9:07

ganapathykumar

3-Feb-05 9:07

hi all

can any body help me how to create dynamic menus in adlg based applications
generating popup menus(CMenu) dynamically ..

Re: creating dynamic menus in dialog based apllications

Ravi Bhavnani3-Feb-05 9:16

Ravi Bhavnani

3-Feb-05 9:16

See TrackPopupMenu().

/ravi

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Re: creating dynamic menus in dialog based apllications

ganapathykumar3-Feb-05 9:23

ganapathykumar

3-Feb-05 9:23

hi pal thanx 4 ur reply,

but i've been using that i nead to create different popup menus at differnt locations

like iam creating a Explorer kind of thing i should get different menus dynamically when i select each item from a tree control of the explorer
for example the windows explorer like...

The menu generated should be changed dynamically when i change my selection in the tree

Re: creating dynamic menus in dialog based apllications

Ravi Bhavnani3-Feb-05 9:28

Ravi Bhavnani

3-Feb-05 9:28

You'll need to dynamically create and populate the menu before displaying it. See CMenu::CreatePopupMenu() and related APIs.

/ravi

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Re: creating dynamic menus in dialog based apllications

uday__m3-Feb-05 17:23

uday__m

3-Feb-05 17:23

hi,
u can look into InsertMenu/ModifyMenu...(MF_POPUP)
hope this is of some help to u!
regards
uday

How to access the Methods from a DLL

ganapathykumar3-Feb-05 9:01

ganapathykumar

3-Feb-05 9:01

hi all,

iam a beginner and iam indulged in a project being developed in VC++

QUESTION:
How to access or manipulate the functions present inside the DLL without knowing the fn()name and the parameter values.plz do help me...

Re: How to access the Methods from a DLL

geo_m3-Feb-05 9:53

geo_m

3-Feb-05 9:53

If you don't know the function name and parameter set, how do you know, what the function does and what it should return?

Re: How to access the Methods from a DLL

ganapathykumar3-Feb-05 9:59

ganapathykumar

3-Feb-05 9:59

ok i accept,

then is there any way to get the fun name and parameter set in a generic way before i access the function from my program , and this all should happen dynamically

Re: How to access the Methods from a DLL

geo_m3-Feb-05 19:15

geo_m

3-Feb-05 19:15

Yes and no. There's a way, how to get the name of the functions, but problem is with parameter set. The best you can get without disassembling is a number of bytes that should be transferred to the function.

If you look at the SDK tool called depends.exe, you'll see what can you get.

If this is enough for you, you can look at the ImageHlp library as described in MSDN. This will help you to parse the info stored inside the dll (which is PE executable)

Re: How to access the Methods from a DLL

RChin3-Feb-05 23:39

RChin

3-Feb-05 23:39

In addition to the above response, you can also use the DumpBin.exe utility to see all publicly exported functions available to you.
The parameters needed and usage will still be needed in advanced though.

I Dream of Absolute Zero

Getting text from a Listbox

Anonymous3-Feb-05 8:50

Anonymous

3-Feb-05 8:50

Hey,
A sort question really. How do I get text from one of the lines in a listbox?
I thought I could do something like this:
SendMessage(listbox1, LB_GETTEXT, 1, 0);
But how should I then use a buffer to save the text?

humpa humpa

Re: Getting text from a Listbox

Ravi Bhavnani3-Feb-05 9:14

Ravi Bhavnani

3-Feb-05 9:14

From the MSDN doc:

LB_GETTEXT 
wParam = (WPARAM) index;                // item index 
lParam = (LPARAM) (LPCTSTR) lpszBuffer; // address of buffer

Parameters:
index
Value of wParam. Specifies the zero-based index of the string to retrieve.

lpszBuffer
Value of lParam. Pointer to the buffer that will receive the string. The buffer must have sufficient space for the string and a terminating null character. An LB_GETTEXTLEN message can be sent before the LB_GETTEXT message to retrieve the length, in characters, of the string.

/ravi

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Re: Getting text from a Listbox

Neville Franks3-Feb-05 9:24

Neville Franks

3-Feb-05 9:24

As Ravi said. Rose | [Rose]

Here is a small example:

/** Get the current selection for the spec'd listbox control.
 *
 *  @param hCtrl_Source Listbox hWnd.
 *  @param szItem returned text.
 *  @param nItemLen size of szItem.
 *
 *  @return list box selection index.
 */
int
GetListboxSel( HWND hCtrl_Source, char* szItem, const int nItemLen )
{
    const int nIndex = (int)::SendMessage( hCtrl_Source, LB_GETCURSEL, 0, 0L );
    if ( nIndex != -1 )   // if list has a selection
    {
        const int nLen = (int)::SendMessage( hCtrl_Source, LB_GETTEXTLEN, nIndex, 0L );
        if ( nLen < nItemlen )
            ::SendMessage( hCtrl_Source, LB_GETTEXT, nIndex, (LPARAM)szItem );
        else
            *szItem = '\0';  // init any crap from callers param
    }
    else
        *szItem = '\0';  // if no selection return empty string
    return nIndex;
}

Neville Franks, Author of ED for Windows www.getsoft.com and Surfulater www.surfulater.com "Save what you Surf"

Re: Getting text from a Listbox

toxcct3-Feb-05 17:18

toxcct

3-Feb-05 17:18

CString strAnswer;
CListBox* pListBox = (CListBox*)GetDlgItem(IDC_MY_LISTBOX_CTRL);
pListBox->GetText(m_plAnswers->GetCurSel(), strAnswer);

TOXCCT >>> GEII power
[toxcct][VisualCalc]

ActiveX on Dialog, and keyboard handling

peterchen3-Feb-05 8:23

peterchen

3-Feb-05 8:23

I'm trying to wrap a pure MFC control into an ActiveX, and use it on an WTL App dialog.

Problem: TAB works spuriosly (it has some functionality within the MFC control's child controls), Return works not at all (the control doesn't see it).

Any ideas?

Here's the deal:

ActiveX Server: ATL DLL with MFC Support
ActiveX control:
ATL Full Control,
the MFC child window is created in OnCreate

Client:
WTL modal dialog based app, Control added to the resource.

Any stuff I need to add/call?
(I tried to add the OnPreTranslateAccelerator and SetFocus that ATL Wizard adds to a full control containing a windows control, but this didn't change anything)

HEEEEEEEEEEEEEEEELP! Blush | :O

[edit]Tabstop does work[/edit]

I never really know a killer from a savior
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dialog based application button press events

Member 4115223-Feb-05 7:34

Member 411522

3-Feb-05 7:34

hello everyone
can anyone tell me how to capture the dialog based control button key press events.i am usin g a vc++.net environement. my requirment is if i have a a button by id IDC_LEFT i want to perform an action as long the button is pressed down and should stop doin the action when released. how do i read that particular action and perform the required action.

anykind of information or help is appriciated.
thanx shashi

Remove maximize option from word document

Anonymous3-Feb-05 6:32

Anonymous

3-Feb-05 6:32

Hi all,

I have a word Add-in from which i will open a word new
document. For this document I want to remove maximize,
resize option. I'm able to remove the resize option using

style &= (~(WS_THICKFRAME));

and applying this style property to the document window using user32.dll
library imported function.

Similarly I tried to remove maximize but its not working.
Any help in this regard is highly appreciated either through C# or
VC++(native).

Thx & Regards
Satish Jupalli

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