Re: Very slow function free() - C / C++ / MFC Discussion Boards

David Crow13-Oct-04 4:02

13-Oct-04 4:02

Allocating memory can be an expensive operation, especially if memory is fragmented. On low-memory machines, asking for 256MB of contigious RAM might involve a lot of paging. Freeing memory instructs the memory manager to access pages previously put on disk. That might be where the latency comes from.

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: Very slow function free()

bschorre13-Oct-04 4:09

bschorre

13-Oct-04 4:09

How can I resolve this problem a little bit more comfortable?

triathlet394

Re: Very slow function free()

David Crow13-Oct-04 4:11

David Crow

13-Oct-04 4:11

I do not know, specifically. Have you tried the new and delete operators instead?

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: Very slow function free()

Blake Miller13-Oct-04 4:27

Blake Miller

13-Oct-04 4:27

Do you really need 256 MB?
Can you break up your data or structure into sub-elements?
You might also try VirtualAlloc instead of using malloc and free.
VirtualAlloc has some options that malloc does not give you.

Re: Very slow function free()

bschorre14-Oct-04 1:49

bschorre

14-Oct-04 1:49

Thanks Blake,

It works really fine. And my programm isn't look big if your looking in the Task-Manager for the memory-usage.

triathlet394

Re: Very slow function free()

Mad__14-Oct-04 1:12

Mad__

14-Oct-04 1:12

Try use GlobalAlloc with GMEM_MOVEABLE flag, this may be work fast.

Re: Very slow function free()

bschorre14-Oct-04 1:46

bschorre

14-Oct-04 1:46

Hi,

I've read that the GlobalAlloc-Function-Group come from the Win 3.x-Framework.

What's the difference between GlobalAlloc and VirtualAlloc?

triathlet394

Re: Very slow function free()

Mad__14-Oct-04 1:57

Mad__

14-Oct-04 1:57

Yes, you right, GlobalAlloc come from Win3.x, but hi work with whole address space, and if you have 256M free in phisical memory, hi get you memory block in phisic memory Wink | ;)

.

And if you use VirtualAlloc function, you mast manage usage of pages.

About speed : GlobalAlloc work some slower then VirtualAlloc, but i didn't think, that is critical (for 256M on Win2k diference less 1s).

Re: Very slow function free()

Henry miller14-Oct-04 2:54

Henry miller

14-Oct-04 2:54

For what complier/C library? malloc/free is not provided by any OS I'm aware of. Instead your C library (which might come with the compiler, might be included) provides it.

In some Unix systems (and I suspect Windows as well), the library asks the OS for more memory than you requested, and then holds that in a buffer. If you malloc more, it will give you memroy from that same buffer if there is room. When you free the memory it marks it unused, but doesn't return it to the OS, instead it will hold onto it in case you need more memory latter.

On many systems the OS will only allow you to allocate 4Kb chunks (this varies depending on both the OS and the design of the hardware). The library is designed so that you can malloc a few bytes, without getting a full 4kb.

Also, in many cases the library will write something to most of that memory when it is allocated. The OS however may just mark your application as allowed to use that much memory, but not actually give it to you, until you use it.

In effect it is optimized for small accesses, and you are sending it a large acccess which it isn't designed for.

If you don't need portability you might be able to speed things up by using OS specific functions to get the memory from the OS yourself.

Note that none of this will help if you don't have enough physical memory. If you want to use 256M of memory you should have at least 400M of physical memory so the OS doesn't have page everything else out.

Change baudrate on opened serial port

smaier3013-Oct-04 3:50

smaier30

13-Oct-04 3:50

Hi there,
How do I change the baudrate of an already opened serial port. I'm pretty sure this should be possible, since I'm about to implement an IEC standard where this behavior is a planned feature.

I'm using the plain VC++ WinAPI what I tried was:

DCB dcb;
GetCommState(m_hFile, &dcb);
dcb.BaudRate = CBR_9600; SetCommState(m_hFile, &dcb);

I get no errors on these opeations, however the connected modem seems simply to time out, I get no more answers from it.

Re: Change baudrate on opened serial port

Vaclav13-Oct-04 6:05

Vaclav

13-Oct-04 6:05

I am not familiar with the WinAPI, but you need to put the modem in "command mode" to set modem parameters. Than switch back to communication / operating mode.

Vaclav

Re: Change baudrate on opened serial port

smaier3014-Oct-04 2:08

smaier30

14-Oct-04 2:08

Ok,
do you know the Hayes code (the modem command set) to change the Baudrate?

create winamp like visualization in wav player?

V.G13-Oct-04 3:10

V.G

13-Oct-04 3:10

I'm creating a wav player and am making use of PlaySound(). Can u please recommend whether to use MCI or continue with the same.. also i need to create a simple bar visualization like the one in winamp.. THANKS!

[edit] how can i play mp3 files in my program?

design patterns - where to start

BlackDice13-Oct-04 3:09

BlackDice

13-Oct-04 3:09

I've seen some articles here on design patterns, but nothing that looks down to my speed. I would like to learn about design patterns, but actually know nothing about them. Does anyone have any suggestions on where I could start?

[insert witty comment here]

bdiamond Sleepy | :zzz:

Re: design patterns - where to start

David Crow13-Oct-04 3:11

David Crow

13-Oct-04 3:11

I know nothing about this, but "fractals" come to mind.

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: design patterns - where to start

BlackDice13-Oct-04 3:15

BlackDice

13-Oct-04 3:15

Huh?

[insert witty comment here]

bdiamond Sleepy | :zzz:

Re: design patterns - where to start

David Crow13-Oct-04 3:27

David Crow

13-Oct-04 3:27

http://dictionary.reference.com/search?q=fractal

http://members.tripod.com/haunt13/fractal.html

http://www.programmersheaven.com/zone10/cat101/

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: design patterns - where to start

BlackDice13-Oct-04 3:32

BlackDice

13-Oct-04 3:32

thanks, I'll look into those!

A brave person isn't always necessarily a smart person

bdiamond Sleepy | :zzz:

Re: design patterns - where to start

BlackDice13-Oct-04 3:41

BlackDice

13-Oct-04 3:41

Sorry, I think you misunderstood my question. I'm not talking about graphics. I mean design patterns as in 'singleton' pattern; applying patterns to frequently encountered programming problems or situations, if I understand the concept correctly.

[A brave person isn't always necessarily a smart person]

bdiamond Sleepy | :zzz:

Re: design patterns - where to start

David Crow13-Oct-04 3:57

David Crow

13-Oct-04 3:57

bdiamond wrote:
Sorry, I think you misunderstood my question.

Like I said, I know nothing about this. Big Grin | :-D

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: design patterns - where to start

hyling13-Oct-04 4:27

hyling

13-Oct-04 4:27

This book will help: <http://www.amazon.com/exec/obidos/tg/detail/-/0201633612/103-7334348-8442222?v=glance>

Hua-Ying

Re: design patterns - where to start

BlackDice13-Oct-04 4:29

BlackDice

13-Oct-04 4:29

what book?

[A brave person isn't always necessarily a smart person]

bdiamond Sleepy | :zzz:

Re: design patterns - where to start

Antony M Kancidrowski13-Oct-04 4:29

Antony M Kancidrowski

13-Oct-04 4:29

There are some good books on Design Patterns

Design Patterns - Addison Wesley - Gamma, Helm, Johnson, Vlissides

is one I would recommend.

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Williams (Little Britain)

Re: design patterns - where to start

BlackDice13-Oct-04 4:34

BlackDice

13-Oct-04 4:34

thanks!! that's what I was looking for!

[A brave person isn't always necessarily a smart person]

bdiamond Sleepy | :zzz:

Re: design patterns - where to start

Kevin McFarlane13-Oct-04 6:26

Kevin McFarlane

13-Oct-04 6:26

See this excellent book. A new edition is imminent.

http://www.aw-bc.com/catalog/academic/product/0,1144,0321247140,00.html[^]

See also http://www.netobjectives.com/dpexplained/[^]

which is the site for the book.

If you have .NET installed and can read C# code try this excellent site:
http://www.dofactory.com/Patterns/Patterns.aspx[^]

See also

Kevin

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