C / C++ / MFC

Did I say something different?

22-Mar-02 14:15

soptest wrote:
Critical section objects can be used only by the threads of a single process!

Critical sections are used when you dont need cross-process suncronization. Only one thread will be allowed access to it.

MSDN snip follows...

[snip]
An object of class CCriticalSection represents a “critical section” — a synchronization object that allows one thread at a time to access a resource or section of code. Critical sections are useful when only one thread at a time can be allowed to modify data or some other controlled resource. For example, adding nodes to a linked list is a process that should only be allowed by one thread at a time. By using a CCriticalSection object to control the linked list, only one thread at a time can gain access to the list.
[/snip]

Regards,
Nish

One Nish is trouble enough.
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soptest22-Mar-02 14:53

soptest

22-Mar-02 14:53

?
soptest

Re: Did I say something different?

Nish Nishant22-Mar-02 16:02

Re: several Threads.....trying to access same array item

22-Mar-02 16:02

oops.

Nish

One Nish is trouble enough.
Imagine 16 of me, dancing wild...
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22-Mar-02 14:18

Nish [BusterBoy] wrote:
You need to use thread synchronization objects.
I suggest a critical section here

What is it? Do you have any example?

Thanks!!!!

Re: several Threads.....trying to access same array item

Nish Nishant22-Mar-02 14:18

Re: several Threads.....trying to access same array item

22-Mar-02 14:18

ChiYung wrote:
What is it? Do you have any example?

You can use the CCriticalSection class.
It has only two member functions you'll need to use.

Create a CCriticalSection object for your app.

Now call m_critsectionobject.Lock() to gain access to the section. Put this as the first line of the array accessing function. Now when other threads call this function, the Lock() will block till the first thread calls Unkock()

Eg:-

void function(...)
{
m_critsectionobject.Lock();

//do your stuff here

m_critsectionobject.Unlock();
}

Now you can safely call function() from multiple threads without fear of two threads accessing the array at the same time.

Nish

One Nish is trouble enough.
Imagine 16 of me, dancing wild...
:jig::jig::jig::jig:
:jig::jig::jig::jig:
:jig::jig::jig::jig:
:jig::jig::jig::jig:

22-Mar-02 14:37

So, in this case, I can do it in this way: (example.....just algorithm....correct me if i am wrong)

This function will be called inside the thread function:

bool function (int x, CString InputString)
{

//can have others stuff here

m_critsectionobject.Lock();

If DBObject[x]= "free"
return true; //lock granted and thread can change DBObject[x] = InputString
Else, return false; //lock not grant and thread need to wait until DBObject[x]="free"

m_critsectionobject.Unlock();

//can have others stuff here
}

Question: If Thread A and B are trying to access the above "Critical section" code, the program will "automatically" create a "QUEUE", so that thread A and B can "line-up" to access this section??

Anyway..........THANK YOU VERY MUCH!!!!!!!!!!!!!!!!!!!!!!!!!!!
You are my angel!!!!!!!!!!!!!!!

Re: several Threads.....trying to access same array item

Nish Nishant22-Mar-02 14:39

Re: several Threads.....trying to access same array item

22-Mar-02 14:39

ChiYung wrote:
Question: If Thread A and B are trying to access the above "Critical section" code, the program will "automatically" create a "QUEUE", so that thread A and B can "line-up" to access this section??

Yes. A and B will NOT access the function in parallel. B will wait till A has called Unlock().

Nish

One Nish is trouble enough.
Imagine 16 of me, dancing wild...
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22-Mar-02 14:49

You are so smart OMG | :OMG:

You gave me a big hands!!!!
Thanks!!!!!!
Laugh | :laugh:

Linking to a Win32 DLL

Don Burton22-Mar-02 13:57

Don Burton

22-Mar-02 13:57

I have a 3rd party Win32 DLL (a PGP wrapper) that I need to call from VC++. All I have is the DLL and a VB .BAS file that outlines the functions declarations as VB would call them.

I'm new to working with Win32 DLLs without an accompanying SDK kit. Can I set up the _stdcall(s) (using the VB code as a guide) or will need a .def or .h file from the DLL?

TIA

Nish Nishant22-Mar-02 14:12

22-Mar-02 14:12

You'll need a header file for the function prototypes, huh? Otherwise it won't compile

Nish

One Nish is trouble enough.
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Don Burton22-Mar-02 14:47

Don Burton

22-Mar-02 14:47

Nish,

Thanks for your quick response.

I have the function prototypes via the VB .BAS file. Can I use those as a guide for the .h prototypes?

Thanks for your help.

Nish Nishant22-Mar-02 14:44

22-Mar-02 14:44

Well even if you have a header file, you'd then need a lib file to link it with. Since you dont have that either, there is no point in making a header file based on the bas file.

Tell you what, dynamically load the DLL and make calls to it. That was the good old fashioned way I guess Smile | :)

Nish

One Nish is trouble enough.
Imagine 16 of me, dancing wild...
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Don Burton22-Mar-02 15:50

Don Burton

22-Mar-02 15:50

That might be the way to go.

Anything I should be aware of if I go that route. (possibly some examples...)

Thanks

Lock a ComboBox

22-Mar-02 13:48

How can I lock a ComboBox from user input (typing). I just want a drop down list (i can use listbox).

Thx

XP

Nish Nishant22-Mar-02 13:58

22-Mar-02 13:58

In the resource editor take Properties-Styles Tab and then set the Type to "Drop List". By default it will be "Dropdown". Now the editable box is replaced with a static one.

Nish

One Nish is trouble enough.
Imagine 16 of me, dancing wild...
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22-Mar-02 15:04

Can I do this dynamically too?

Nish Nishant22-Mar-02 15:19

22-Mar-02 15:19

Anonymous wrote:
Can I do this dynamically too?

I am not sure about that. Some styles cannot be changed at run time. But try setting the CBS_DROPDOWNLIST style using ModifyStyle

Nish

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Imagine 16 of me, dancing wild...
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Re: Lock a ComboBox [2]

Nish Nishant22-Mar-02 15:22

22-Mar-02 15:22

Anonymous wrote:
Can I do this dynamically too?

I just tried this out :-

ModifyStyle(CBS_DROPDOWN,CBS_DROPDOWNLIST);

Didn't work Frown | :-(

Nish

p.s. Perhaps there are other ways available. But I am not too sure now.

One Nish is trouble enough.
Imagine 16 of me, dancing wild...
:jig::jig::jig::jig:
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Shog⁹22-Mar-02 16:19

Shog⁹

22-Mar-02 16:19

Check out this nifty little control.

_{And if words were wisdom, I'd be talking even more.}

The Offspring, I Choose

Can't connect...

Rickard Andersson²⁰22-Mar-02 12:14

Rickard Andersson²⁰

22-Mar-02 12:14

This is not realy a programming questin... but people can't connect to my socket apps.... 'm using WinMe and I have a mini network at home here...

------------------------------------
Rickard Andersson, Suza Computing
ICQ#: 50302279
I'm from the winter country SWEDEN!

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

Re: Can't connect...

Nish Nishant22-Mar-02 13:55

22-Mar-02 13:55

Is your sockets app running on a machine with an IP that is accesible from outside?

Nish

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Imagine 16 of me, dancing wild...
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NC22-Mar-02 10:38

22-Mar-02 10:38

Hi!
Can you use a submenu of your dlg's main menu(like edit or file) as a popup menu too, using TrackPopUpmenu()? If so, will the command and updatecommand messages be handled automatically?

NC

Re: Menu

Nish Nishant22-Mar-02 13:53