GetMem vs VirtualAlloc

[Michael Lv]

Hi

In Borland's Documentation, routine GetMem() implements VirtualAlloc()
internally. But I write a demo and find GetMem only allocate 500M memory and
VirtualAlloc can allocate upper 1G memory in my 256M physical memory PC.

Anyone can try to access a Big file(size > your physical memory) with
GetMem() and see result.

My question is :
(1),Do GetMem() implement Virtual Memory Management internally? Need I
use VritualAlloc() straight?
(2), If (1) is No, so how can I implement Virtual Memory Management? Use
VirtualAlloc() or select a right Memory Manager in Delphi?

Thanks!

Michael Lv

[Tomaz Koritnik]

Hi

For both functions a limit is 2GB. This is because in win32 enviroment,
all applications can allocate up to 2GB of memory (exactly 2^31 or 2^31 -
1). This, of course, is a virtual limit, whereas physical limit is the sum
of physical RAM and page file size.

Tomaz

"Michael Lv" <leisu...@263.net> wrote in message
news:3dec42c4$1...@newsgroups.borland.com...

[Michael Kelly]

Michael Lv wrote:

> No, so how can I implement Virtual Memory Management? Use
> VirtualAlloc() or select a right Memory Manager in Delphi?

You might also want to check out the HeapAlloc() Win32 API.

--

"Only choice is an oxymoron."

[Michael Lv]

I mean, although I can use VirtualAlloc() function to request virtual memory
allocation, but I can't control Delphi's internal memory management. For
instance, I create a class containing big string object. I write

MyObj := TMyObj.Create;

Can you tell me MyObj use heap memory or virtual memory?

Michael Lv

[John Herbster \(TeamB\)]

"Michael Lv" <leisu...@263.net> wrote

> MyObj := TMyObj.Create;
> Can you tell me MyObj use heap memory or virtual memory?

Michael, I think that nearly all of a Windows' applications memory
can be swapped out to the disk swap area. I am guessing that that
is what you mean by virtual. I believe that there is a way to limit
such swapping, but I have never used it. Why were you asking?
Regards, JohnH

[Michael Lv]

Thank you, John

Yes, MS use swapping files to implement virtual memory
management(right?). At past, I think GetMem() encapsulate internal virtual
memory management mechanism, so I use GetMem() function to access a 500M
file in my PC with only 256M physical memory. GetMem() can only allocate
about 400M memory for process and Windows raise "Out of Memory" exception.
I use VirtualAlloc() API to access file directly and make things better,
which can get upper 1G virtual memory. But I can't resolve such
memory-allocating like "TObject.Create", which be controlled by Delphi's
internal memory allocation mechanism. So my question is :
1, Can we believe GetMem() function for virtual memory allocation?
2, How can I manipulate memory allocation like "TObject.Create"?

Thanks!

[scott_maskiel isat removeifnotspammer.nemmco.com.au]

memory-allocating like "TObject.Create", which be controlled by Delphi's
> internal memory allocation mechanism. So my question is :
> 1, Can we believe GetMem() function for virtual memory allocation?
> 2, How can I manipulate memory allocation like "TObject.Create"?
>
> Thanks!
>

Hi Michael,

Not sure about No. 1, but with No.2 you can declare your own class and
override the NewInstance method. NewInstance is responsible for
allocating an object's memory.

Regards,
Scott