C / C++ / MFC Discussion Boards

Mattias G15-Jan-10 3:44

15-Jan-10 3:44

Could you provide an example of where multi-threading is a good idea? Would be interesting to hear from someone with good experiences from threads ...

Re: Execute two classes

Cedric Moonen15-Jan-10 4:07

Cedric Moonen

15-Jan-10 4:07

There are a lot of cases where multi-threading is an advantage.
For instance, when you have a server (probably even without a UI) that should accept different clients at the same time. I can't imagine doing something like that without mutli-threading.
Another example: if you have an application which has to execute tasks (which can be a lenghty operation) and you don't want to freeze the UI. Of course, you could use the OnIdle but this becomes quickly difficult to manage. It is much easier to have a queue object in which you can enqueue the tasks when needed and the queue object processes these tasks in a separat thread, independantly of the UI.

Of course, there are much more examples than that.

Cédric Moonen
Software developer

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Re: Execute two classes

Rajesh R Subramanian15-Jan-10 5:18

Rajesh R Subramanian

15-Jan-10 5:18

The simplest case would be where you have to wait on a port for data, or you've to wait for an operation to complete, or you have to do a lengthy processing, while still having to keep the GUI responsive.

"Avoid multithreading at all costs" is probably the worst advice I've ever seen here.

“Follow your bliss.” – Joseph Campbell

Re: Execute two classes

CPallini15-Jan-10 5:42

CPallini

15-Jan-10 5:42

Have a look at Idle Loop Processing, namely:

Many applications perform lengthy processing "in the background." Sometimes performance considerations dictate using multithreading for such work. Threads involve extra development overhead, so they are not recommended for simple tasks like the idle-time work that MFC does in the OnIdle function. This article focuses on idle processing. For more information about multithreading, see Multithreading Topics.

Some kinds of background processing are appropriately done during intervals that the user is not otherwise interacting with the application. In an application developed for the Microsoft Windows operating system, an application can perform idle-time processing by splitting a lengthy process into many small fragments. After processing each fragment, the application yields execution control to Windows using a PeekMessage loop.

Aside of performance considerations, I've underlined the key concept behind idle time processing: you need to fragment a lenghty operation. That means you've to build a state machine. Of course it is a viable approach but using a separate thread means that, conceptually, the execution flow is never broken.
Multithreading requires care, I admit, but you cannot deduce by your bad experience with, that multithreading is bad.
Smile | :)

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Re: Execute two classes

Mattias G19-Jan-10 3:23

Mattias G

19-Jan-10 3:23

(Late reply, but anyways) Ok, multi-threading isn't always bad Smile | :)

It's just that I have seen very few examples where multi-threading brings any real benefits -- a server app as mentioned above might be one, a device driver might be another. On the other hand, I've seen a few extremly tricky maintenance and debugging problems due to MT. For starters, it can be almost impossible just to reproduce a certain behaviour or error in a application with multiple threads. I would probably prefer a state machine in 9 out 10 cases.

/M

Re: Execute two classes

CPallini19-Jan-10 3:29

CPallini

19-Jan-10 3:29

State machines are good. But, for many programmers counter-intuitive.
Smile | :)

Re: Execute two classes

CPallini15-Jan-10 2:44

CPallini

15-Jan-10 2:44

Mattias G wrote:
Multi-threading should be avoided at all costs.

Mattias G wrote:
Do not use multi-threading, I cannot stress this enough.

Mattias G wrote:
I speak from bitter experience

No, you are speaking from Bitter [^] experience... Roll eyes | :rolleyes:

sorry for that, it was...irresistible to me

Working with POP3 from Win32 application

VictorSotnikov14-Jan-10 22:05

VictorSotnikov

14-Jan-10 22:05

Hi
Please help me choose how (an API, component, library etc) can I work with POP3 in the following task. I have no experience with POP3 and do not know where to start.

I have C++ Win32-application (MS Visual C++ 2005 or 2008) that must:
- periodically (say once in 5 min) check a mailbox via POP3
- retrieve new messages from there, process them (the processing is specific for the my task) and remove the processed messages.

The question is: what (an API, component, library etc) should be used for this task? Most probably there will be several solutions - if so, please recommend better one.

If, say, there is a ready component that resolves the task, but it is implemented on .Net - how easy to integrate it with C++ application?

Thanx

Re: Working with POP3 from Win32 application

«_Superman_»14-Jan-10 22:15

«_Superman_»

14-Jan-10 22:15

POP3 has several commands that are used to retrieve mails, delete mails etc. from a POP3 server.

In Windows you can use sockets to connect to a POP3 server using its IP address and port. (The default port for POP3 is 110).

After this it is just a matter of sending commands and receiving the response.

Read about the POP3 commands and the protocol here - RFC1939 - Post Office Protocol - Version 3[^]

«_Superman_»
I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Re: Working with POP3 from Win32 application

VictorSotnikov14-Jan-10 22:38

VictorSotnikov

14-Jan-10 22:38

Thanx. But I also wanted to know - is there some component that implements basic functionality for this task - to avoid writing 'from scratch'. This could be:
- interaction with sockets
- password-related stuff

Re: Working with POP3 from Win32 application

Stuart Dootson14-Jan-10 22:54

Stuart Dootson

14-Jan-10 22:54

Have you tried looking on Google?

Some freeware options:

here[^] and here[^] (POCO has a class implementing POP3 client functionality)

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

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Re: Working with POP3 from Win32 application

Moak14-Jan-10 22:57

Moak

14-Jan-10 22:57

There are a couple of articles, see http://www.codeproject.com/KB/IP/[^] and for example CPop3Connection v1.19[^].

Hope this helps

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Re: Working with POP3 from Win32 application

Joe Woodbury15-Jan-10 6:06

Joe Woodbury

15-Jan-10 6:06

POP3 is pretty simple, but if you want a quick solution, check out IP*Works from nSoftware: http://www.nsoftware.com/[^] (The cost of this is probably less than how much it would cost to write it yourself.)

Re: Working with POP3 from Win32 application

VictorSotnikov17-Jan-10 22:06

VictorSotnikov

17-Jan-10 22:06

Thank you for the replies

During this time my task became more complicated ( Smile | :)

) Now I should not only receive mails via POP3 but also convert body of received mail into plain text (WCHAR* string). I mean: to convert removing formatting elements like HTML tags (when a mail is in HTML format) etc., leaving only text. Now I am not interested in content of attachments - I need only mail's text.

The question is: do you know a component that can solve the task too? Or: one component to read POP3, another one for extracting text from received e-mail. The components may be commercial ones (my employer is rich enough to pay for them Wink | ;-)

Re: Working with POP3 from Win32 application

Joe Woodbury17-Jan-10 22:17

Joe Woodbury

17-Jan-10 22:17

I have not used IP*Works to the fullest extent, but when I did, I recall that it did everything with POP3 and SMTP. It's a very nice library.

Need help in creating c++ stubs.

Maya_14-Jan-10 20:37

Maya_

14-Jan-10 20:37

Hi Everyone,

I'm working on a NT service which calls other Services in another machine. I know that for unit testing we can write stubs for other remote services to test the service. I've searched on the net but i couldn't find any tutorial to do this. Can anyone please tell me how to write stubs (the basic idea, i've absolutely no idea where to start) or direct me to any tutorial that would help me??

Regards,

Re: Need help in creating c++ stubs.

Richard MacCutchan14-Jan-10 21:19

Richard MacCutchan

14-Jan-10 21:19

You just write a method with the same signature as the 'real' function, and add your own code to return a good or bad status as appropriate. For example the Windows function GetFileVersionInfo() could be coded like this

BOOL GetFileVersionInfo(LPCTSTR lptstrFilename,
    DWORD dwHandle,
    DWORD dwLen,
    LPVOID lpData
)
{
    OutputDebugString("My test");

    return TRUE;
}

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Which windows datatype to store LSN (Number upto 25 digits)

s v joshi14-Jan-10 20:27

s v joshi

14-Jan-10 20:27

SQL server database can have LSN number(Log sequence number) in 25 digit
so maximum value of that LSN can be 9999999999999999999999999
that is 25 times 999...

I cannot use string to store it because i need to perform some arithemetic operations like addation,substrication on it

so in C++ which datatype can i used to store it.

Re: Which windows datatype to store LSN (Number upto 25 digits)

CPallini14-Jan-10 20:40

CPallini

14-Jan-10 20:40

s v joshi wrote:
C++ which datatype can i used to store it

There isn't.
You may store your number into two __int64 variables.
Another option would be using a big integer library, like, for instance, the GNU GMP.
Smile | :)

Re: Which windows datatype to store LSN (Number upto 25 digits)

Nelek14-Jan-10 20:44

Nelek

14-Jan-10 20:44

Is __int256 not an option?

I guess is not standard, but there are quite hits in google for 128 and 256 integers.

Regards.
--------
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Help me to understand what I'm saying, and I'll explain it better to you
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Re: Which windows datatype to store LSN (Number upto 25 digits)

CPallini14-Jan-10 20:50

CPallini

14-Jan-10 20:50

Nelek wrote:
Is __int256 not an option?

A __int128 would be enough. Anyway it is not a built in type. You may find a lot of available solution on the web, I suppose (or you may roll your own, it is amusing...).
Smile | :)