C / C++ / MFC Discussion Boards

Daniel Turini24-Oct-02 11:41

24-Oct-02 11:41

Rickard Andersson wrote:
and did you mean that EnterCriticalSection will lock for ever if I don't have an __try/__finally statement?

MAY lock forever, not WILL lock forever.

If you have a bug in the code between the Enter/Leave pair, your code may not execute the Leave part, leaving the CS locked forever.
So, take care with the code you put between this.
That's why the __try/__finally is there: as an assurance that the Leave will execute always, even on crash or error situations.

Q261186 - Computer Randomly Plays Classical Music

Re: Critical sections (Moak & Co.)

Joe Woodbury24-Oct-02 11:50

Joe Woodbury

24-Oct-02 11:50

I personally don't like the __try/__finally. If an error happens that leaves the global data in an unstable state, simply releasing the critical section, absent anything else, isn't going to make the code any more stable and arguably less.

Re: Critical sections (Moak & Co.)

Joe Woodbury24-Oct-02 11:35

Joe Woodbury

24-Oct-02 11:35

Basically yes. Be aware, however, that the critical section should be as short as possible to prevent thread stalling. I would examine your global data carefully to make sure you aren't guarding things that don't need guarding.

In other words, if the global data in question is a series of unrelated items, you don't want to guard all of them with a single critical section; a common mistake.

Also be aware that if you need to share a single value, check out the Interlocked...() series of calls.

Re: Critical sections (Moak & Co.)

Rickard Andersson²⁰24-Oct-02 11:40

Rickard Andersson²⁰

24-Oct-02 11:40

Joe Woodbury wrote:
I would examine your global data carefully to make sure you aren't guarding things that don't need guarding.

I'm working on a server that will save all clients in a global std::list object. When a client whants to send to another client on the server, the client iterate through the std::list object and send the message to all clients.

Isn't it good Unsure | :~

to make a critical section here?

Rickard Andersson@Suza Computing
C# and C++ programmer from SWEDEN!
UIN: 50302279
E-Mail: nikado@pc.nu
Speciality: I love C#, ASP.NET and C++!

Re: Critical sections (Moak & Co.)

Joe Woodbury24-Oct-02 11:55

Joe Woodbury

24-Oct-02 11:55

Yes. I think (I'm still not clear how many threads you have, etc.)

(Since it looks like you have a one writer, multiple readers issue, the CriticalSection will block all readers even when a write isn't being done. However, there is no synchronization object designed specifically for this, though you can make a compound object. I have and in real world testing it was much slower than plain Critical Sections. However, this assumes that the read operations are extremely short and can easily occur in a single time slice.)

Re: Critical sections (Moak & Co.)

Rickard Andersson²⁰24-Oct-02 21:38

Rickard Andersson²⁰

24-Oct-02 21:38

Joe Woodbury wrote:
I'm still not clear how many threads you have, etc.)

I will have about 100 threads only.
perhaps 150, but for now 100 is what the first version of my server will have.

Joe Woodbury wrote:
(Since it looks like you have a one writer, multiple readers issue, the CriticalSection will block all readers even when a write isn't being done. However, there is no synchronization object designed specifically for this, though you can make a compound object. I have and in real world testing it was much slower than plain Critical Sections. However, this assumes that the read operations are extremely short and can easily occur in a single time slice.)

But if don't make up a critical section when I read the object?
As Moak said in the message down here it is always safe to READ a global data in multiply threads. then it would be safe, wouldn't it?

Rickard Andersson@Suza Computing
C# and C++ programmer from SWEDEN!
UIN: 50302279
E-Mail: nikado@pc.nu
Speciality: I love C#, ASP.NET and C++!

Re: Critical sections (Moak & Co.)

Joe Woodbury25-Oct-02 1:09

Joe Woodbury

25-Oct-02 1:09

You should seriously consider using I/O completion ports. It's perfect for what you're doing.

Re: Critical sections (Moak & Co.)

Rickard Andersson²⁰25-Oct-02 5:53

Rickard Andersson²⁰

25-Oct-02 5:53

Where can I read more about that!?

Rickard Andersson@Suza Computing
C# and C++ programmer from SWEDEN!
UIN: 50302279
E-Mail: nikado@pc.nu
Speciality: I love C#, ASP.NET and C++!

Re: Critical sections (Moak & Co.)

Joe Woodbury25-Oct-02 6:46

Joe Woodbury

25-Oct-02 6:46

The MSDN documentation has a hopelessly incomplete description. The best discussion is in an out-of-print Jeffrey Richter book "Programming Server-Side Applications for Microsoft Windows 2000."

Perhaps, someone should ask Richter if CP can "reprint" the chapter.

Re: Critical sections (Moak & Co.)

Moak24-Oct-02 19:35

Moak

24-Oct-02 19:35

Rickard Andersson wrote:
I'm working on a server that will save all clients in a global std::list object. When a client whants to send to another client on the server, the client iterate through the std::list object and send the message to all clients.

Hej Rickard,
with a mutithreading socket concept this is a must have IMHO. Reading isn't critical, but changing or removing elements from a list: Another task could e.g. remove an element from the list (when a client signs off), which could invalid the iterator used by another thread. So, that's why you have to make exclusive access to your global network data, no matter if threads wants to read or write.

Re: Critical sections (Moak & Co.)

Rickard Andersson²⁰24-Oct-02 21:39

Rickard Andersson²⁰

24-Oct-02 21:39

Thaaaaaaaaaaank you Moak!
See your ICQ for an important message from me! Smile | :)

Rickard Andersson@Suza Computing
C# and C++ programmer from SWEDEN!
UIN: 50302279
E-Mail: nikado@pc.nu
Speciality: I love C#, ASP.NET and C++!

Re: Critical sections (Moak & Co.)

Anonymous24-Oct-02 22:08

Anonymous

24-Oct-02 22:08

no problem... mompl, starting ICQ... Smile | :)

How to detect a CView closing?

Ravi Bhavnani24-Oct-02 11:19

Ravi Bhavnani

24-Oct-02 11:19

[ Returning to the doc-view architecture after 8 years, so excuse the lameness of this question! ]

I have an MDI app that's capable of displaying documents of type CFooDoc and CBarDoc. I've modified the file opening logic to restrict the number of open CFooDoc documents to 1.

What I want to do is automagically close all CBarDoc documents when the user closes the solitary CFooDoc document. I can do this by calling the CloseAllDocuments() on CBarDoc's doc template.

My question is, how do I detect that the CFooView is closing?

Thanks,

/ravi

Let's put "civil" back in "civilization"
http://www.ravib.com
ravib@ravib.com

Re: How to detect a CView closing?

Ravi Bhavnani24-Oct-02 11:20

Ravi Bhavnani

24-Oct-02 11:20

Never mind. Smile | :)

I just overrode the parent frame's OnClose().

/ravi

Let's put "civil" back in "civilization"
http://www.ravib.com
ravib@ravib.com

Re: How to detect a CView closing?

Neville Franks24-Oct-02 12:00

Neville Franks

24-Oct-02 12:00

Hi Ravi,
Or in ~CFooView() or CFooView::PostNCDestroy() or ...

Neville Franks, Author of ED for Windows. www.getsoft.com

Re: How to detect a CView closing?

Ravi Bhavnani25-Oct-02 1:42

Ravi Bhavnani

25-Oct-02 1:42

Hi Neville,

Actually the tack I took only handled the case when the user closed the view manually by clicking the "x" button. It didn't handle the ID_FILE_CLOSE case, so I used a custom command and handled document closure myself.

/ravi

Let's put "civil" back in "civilization"
http://www.ravib.com
ravib@ravib.com

Menu in a dialog

sikrip24-Oct-02 11:14

sikrip

24-Oct-02 11:14

Hi,
how can i add a menu in a dialog based application??

Re: Menu in a dialog

Ravi Bhavnani24-Oct-02 11:21

Ravi Bhavnani

24-Oct-02 11:21

Create a menu in the resource editor, then modify the dialog's "Menu" property (also in the resource editor) to point to that menu.

/ravi

Let's put "civil" back in "civilization"
http://www.ravib.com
ravib@ravib.com

Re: Menu in a dialog

Anonymous24-Oct-02 18:35

Anonymous

24-Oct-02 18:35

the first,you create a new menu whit ID_DLG_MENU
the second,see the dialog property.
select the ID_DLG_MENU int the Menu:

change dialog font

lucy24-Oct-02 10:54

lucy

24-Oct-02 10:54

I have a dialog template. I create a CPropertyPage class on it, and add it to my property sheet.

On this dialog, I have a combo box as a drop list. My question is: the combo box content is added at run-time. Its string format is as follows:
%2d: %-35s %02d

The problem is: using the default font, the string part will have variable length. I tried to overwrite the OnSetFont() as:

// use another font instead of the default one
if ( HFONT(myFont) ) // my font is created in the constructor and deleted in destructor, declared as a member variable
{
    pFont->DeleteObject();
    pFont = &myFont;
}

CPropertyPage::OnSetFont(pFont);

I have tried to use different font, "Arial", "Courier", "System", "Times New Roman", but all of them gave me a big bold ugly font displayed on the dialog. Confused | :confused:

what's the correct way to do it?

Thank you a lot!

Re: change dialog font

alex.barylski24-Oct-02 13:24

alex.barylski

24-Oct-02 13:24

I'm not sure I understand what the problem is...

Your string part will be variable width...? Whys that a bad thing...?

I suppose your gonna wanna use a fixed width font like Courier New (Courier should work also???)

What are you trying to acocmplish...? Just change the font..?

Do it inside InitDialog() with a call to the controls SetFont()

"An expert is someone who has made all the mistakes in his or her field" - Niels Bohr

CList and sockaddr_in

User 665824-Oct-02 9:47

User 6658

24-Oct-02 9:47

Hi
I want to store IPs in a linked list using CList, but don't know how to do that. Servers already in the list should not be stored in the list again. Currently I can't compile my project due to errors.
This is what I want to do:

CList<sockaddr_in, sockaddr_in&> SockList // <- is this correct?

for(int i=0; i<num_servers; i++)
{
    // check whether server is already in the list
    if(SockList.Find(server) == NULL) // server is not in list
          SockList.AddTail(server);
}

server is of type sockaddr_in*.
How can I achieve this?

thanks in advance
Greg

modified 12-Sep-18 21:01pm.

Re: CList and sockaddr_in

valikac24-Oct-02 9:59

valikac

24-Oct-02 9:59

You cannot search a list of pointer using its default equality comparison.

I recommend an STL list or map and with a custom equality or equivalent search algorithm via a function object.

Kuphryn

Re: CList and sockaddr_in

User 665824-Oct-02 10:19

User 6658

24-Oct-02 10:19

Thanks

Is there no way to copy the values of a sock_addr* pointer into a normal sock_addr variable?
This way it would be possible, or am I wrong? Confused | :confused:

regards

modified 12-Sep-18 21:01pm.

Re: CList and sockaddr_in

valikac24-Oct-02 10:50

valikac

24-Oct-02 10:50

Consider memcpy(). I am not completely sure that will work for sock_addr.

Kuphryn

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