Modifying malloc( ) implementation, without changing malloc( ) source code

I have a big chunk of memory (128M), which is divided into 4 memory banks.. Now, I am supposed to make efficient memory utilization,and for that purpose, I NEED TO ALLOCATE MEMORY FROM THE ADDRESSES I PROVIDE. Now, here's what the problem... We have a system defined malloc( ) source which I'm not supposed to change.
So, one way I can think of is...
do a malloc and compare with the address I want to allocate memory at.
if not equal, then call malloc again, & free the previous memory
continue this till I reach the address I want to allocate memory at

But this is really very inefficient and slow method..

Since I'm not supposed to change the malloc source code,
Does somebody have any idea how to trick the heap manager, or by some pointer manipulations, or by writing wrapper routines, anyway, so that I can allocate a memory chunk at the address I provide.

Please help,

im sorry its not possible.

If you have a fixed chunk of memory that already has been allocated, then you do not need to worry about malloc or the system memory manager.

What you want is a memory pool. You need to create one or more classes which keep track of the parts of your chunk of memory which are in use and the parts which are not in use and allow other classes to 'allocate' and 'free' memory in that memory range.

I am sorry if I didn't get you properly.
Now, I already have a memory pool. It is divided into say 4 parts, each one a memory bank.
Now, even if I have different classes, they all are ultimately going to call malloc, which would automatically allocate memory from the heap as available, but what I want is write some routine which would allocate that particular chunk at the address I provide

Why do they need to call malloc? Why can they not call your own memory management functions?

If for some reason the other functions must call malloc / free, then there are only two options I can see:

Do not link to the default implementation of malloc but write your own implementation of malloc (but it sounds like you are not allowed to)

or

#define malloc mempool_malloc
#define free mempool_free


for the code that needs to use that memory range. This second option is not recommended.

Quote:

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Originally Posted by abheei25

what I want is write some routine which would allocate that particular chunk at the address I provide

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is this adress inside one of your "memory banks" or not?

Quote:

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Originally Posted by Mitsukai

is this adress inside one of your "memory banks" or not?

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Yes, the address provided would be in one of the memory banks, since we are dividing the available space into different memory banks

Quote:

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#define malloc mempool_malloc
#define free mempool_free

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even if I write different implementation for malloc, it is ultimately the heap manager which allocates the space as available, so I don't think this would work fine(?)

k this is what u do..

Code:

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void* myalloc(const size_t size)
{
  static unsigned char bank[4][128 * 1024];
  //manage your **** here
  //and return the open memory.
}

---

Quote:

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Originally Posted by Mitsukai

Code:

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void* myalloc(const size_t size)
{
  static unsigned char bank[4][128 * 1024];
  //manage your **** here
  //and return the open memory.
}

---

---

But even after deriving a particular address from the implementation, it is the heap manager that actually allocates the memory, so how would I get the heap manager to allocate space of "size" capacity at the address I provide

Can you please the implementation part??

you just asked the hardest part...

i jsut want to ask why u are u doing this, the operating system should take care of the dynamic allocation....

ok.. first u must somehow know where are all the allocations made. u can make another array for this. actually use an array of pair<pointer, size> so u know where evything is allocated... you could also use set instead of an array so you can insert the paird ordered and increases speed for searching for open memory.

i really think you should do this for yourselve, and if you encounter any problems i can help you further.

Quote:

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Originally Posted by abheei25

how would I get the heap manager to allocate space of "size" capacity at the address I provide

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For that, you need to use an OS specific call.

In Windows, you can use VirtualAlloc.

Quote:

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Originally Posted by Zaccheus

For that, you need to use an OS specific call.

In Windows, you can use VirtualAlloc.

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thats not what he wants, he wants to make a memory manaager hisselve, this adreess hes talking about is in his allocated memory "banks"

There's a parallel thread here:
http://www.codeguru.com/forum/showthread.php?t=415096

Quote:

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Originally Posted by abheei25

Yes, the address provided would be in one of the memory banks, since we are dividing the available space into different memory banks



even if I write different implementation for malloc, it is ultimately the heap manager which allocates the space as available, so I don't think this would work fine(?)

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this is what he sayd. and i gave him the correct answer

Quote:

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Originally Posted by abheei25

... how would I get the heap manager to allocate space of "size" capacity at the address I provide ...

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;)

Let's just see what he says.
:)

Hello,

Why don’t you override the global new operator?

In the other thread he explained that he's doing this in C. My understanding is that he needs the system's heap manager to allocate a specific address range.

Then, why not use #define?

Code:

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#include <stdlib.h>

void* MyAlloc(size_t)
{
  void* p;
  // ...
  return p;
}
#define malloc(s) MyAlloc(s)

int main()
{
  void* p = malloc( 1 ); // MyAlloc will be called instead of stdlib malloc
  return 0;
}

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It's the

Code:

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// ...

---

that we are having a small problem with.

:)

As I posted in the other thread...

Code:

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sometype *ptr = 0x040000;

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If the address is sized, and no other resource is going to try to use it. Not enough information posted (in either thread) to know....

Quote:

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Originally Posted by TheCPUWizard

Not enough information posted (in either thread) to know....

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Yeah, I agree, we don't even know if he is running inside Windows' virtual address space.

Quote:

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Originally Posted by Zaccheus

It's the

Code:

---

// ...

---

that we are having a small problem with.

:)

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So... he needs a memory manager to manage the memory pool?... And this new manager must work better than the original one? :eek:

I think he wants to allocate memory at a specific address, which is why I suggested VirtualAlloc, but it's really not very clear whether that function is what is needed.