C / C++ / MFC

1-Mar-04 2:48

Do I need to synchronize simple data types (int, DWORD, bool etc.), when I write to the (static) variable in one thread and read it in another. Does windows ensure that it will not switch to another thread during writing of one value? What do I have to remark.
Thanks for any answer.

Regards Konrad

Prakash Nadar1-Mar-04 3:04

1-Mar-04 3:04

different thread will not write or read or write/read the values at the same time... but a thread can set a bool value to false just after you have read it as true.
So that could cause a problem, Its better to have critical sections for these static variables.

P.R.A.K.A.S.H

Konrad Windszus1-Mar-04 4:08

1-Mar-04 4:08

But I think i need to declare the static variable with the keyword volatile, or is this not correct?

Konrad

Prakash Nadar1-Mar-04 4:43

1-Mar-04 4:43

yeah it should be volatile.

Jo hoga, Kuddhaye manjur hoga.

Joe Woodbury1-Mar-04 18:35

Joe Woodbury

1-Mar-04 18:35

Look at the InterlockedExchange() and related calls.

(on a 80x86 based system, a bool or char will be read/written in an atomic operation, though I don't advise it outside of very narrow circumstances.)

Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke

Konrad Windszus2-Mar-04 0:20

2-Mar-04 0:20

Thank you very much, that helps. But with InterlockExchange I must write a new value to a variable. What if I just want to read variable and ensure that this is atomic?

Do the variable have to be declared as volatile.
Sorry but the MSDN library is very short concerning this issue.

Konrad

Robert A. T. Káldy2-Mar-04 1:04

Robert A. T. Káldy

2-Mar-04 1:04

If you only read the variable, you don't need to synchronize anything Smile | :)

If you simultaneously read and write to the variable, only the writing operation should be interlocked.

Robert-Antonio

"Life is very hard, when you apply E-R model to it."

Konrad Windszus2-Mar-04 2:14

2-Mar-04 2:14

Thanks for your answer, but in the MSDN Library I found the following sentence:

Simple reads and writes to properly-aligned 32-bit variables are atomic.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/base/interlocked_variable_access.asp

What about other variables like char (8bit)? Isn't it possible, that during the read process another thread writes to the variable with InterlockedExchange. After this the read thread is reading the second part of the variable. It gets corrupted, because it wasn't an atomic read. What about other variables like 8, 16 bit. Are reads always atomic?

And do I need volatile for these variables if I write to them only via InterlockedExchange.

Thanks for any answer
Konrad

Joe Woodbury2-Mar-04 5:31

Joe Woodbury

2-Mar-04 5:31

You do not need to use volatile if using InterlockedExchange.

Reads/writes to/from 8 bit values are atomic on x86 platforms.

Do note that if you must guarantee a specific sequence of reading and writing, you'll need to use more complex synchronization methods.

Anyone who thinks he has a better idea of what's good for people than people do is a swine.
- P.J. O'Rourke

Query: Display Line Number infront of each Line of source (MFC)

Robert A. T. Káldy2-Mar-04 5:33

Robert A. T. Káldy

2-Mar-04 5:33

I think you're right. 8- and 16-bit writing should be atomic too. The operation is made by only one assembler instruction MOV.
Volatile declaration is necessary, because it tells to compiler, that its value may be changed every time by another thread. For example, if you're referring to the variable multiple times in one thread, the compiler should optimize it by storing its value in register. If another thread changes the value, you have a different value in memory and register and the program could not behave correctly. Volatile declaration ensures, that the value of variable is always taken from the memory.

Robert-Antonio

"Czech Railways discovered, that in case of disaster the most damaged wagons
were the first and the last. So they decided to create trains without them."

irshad_bukhari1-Mar-04 2:46

irshad_bukhari

1-Mar-04 2:46

Hi,

I want to open & display a file(ex: .C) with Line Number to be displayed infront of each line. (Ex: Like C Debugger have)

Plz. send me code if anybody written...
irshad_b@indiatimes.com

Thanks in Advance,

Regards,
Irshad

Re: Query: Display Line Number infront of each Line of source (MFC)

Prakash Nadar1-Mar-04 2:57

Re: Query: Display Line Number infront of each Line of source (MFC)

1-Mar-04 2:57

I know how to do it, but i am not going to write a code for you.but hey how lazy can you get?

P.R.A.K.A.S.H

David Crow1-Mar-04 3:01

David Crow

1-Mar-04 3:01

Assuming you have an edit control with the ES_MULTILINE style, you can do something like:

CStdioFile file(_T("c:\\boot.ini"), CFile::modeRead);
CString strFileLine,
        strEditLine;
int nLine = 1; 
    
while (file.ReadString(strFileLine) != FALSE)
{    
    strEditLine.Format(_T("%d %s\r\n"), nLine++, (LPCTSTR) strFileLine);    
    m_edit.ReplaceSel(strEditLine);
}

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: Query: Display Line Number infront of each Line of source (MFC)

irshad_bukhari1-Mar-04 21:53

irshad_bukhari

1-Mar-04 21:53

Thanks for ur reply..

Sorry i am asking silly questions..as I am new to MFC...Actually i want to
1. open C source file with standard coloring of keywords of C langauge ..&
2. a new view window which display line number & have capabilty to set break-points ..(like M VC++ editor have)
3. a shared vertical scroll-bar between these windows.

I am using RichEditView class for other operations like get line number on double-clk,etc..

Regards
Irshad

debug a service

Anonymous1-Mar-04 2:41

Anonymous

1-Mar-04 2:41

what is the best way to debug a service in vs 6.0..

Re: debug a service

Prakash Nadar1-Mar-04 2:56