CODEWITHSUNDEEP
c++memorymemory-management
MulletDevil
MulletDevil

Reputation: 909

using a vector in a custom memory manager

I am writing a memory manager in c++. The aim is to allocate a set amount of memory at the start using malloc and then overload new and delete so that it uses that memory. I almost have it working my only problem is how i am keeping track of what is where in the memory.

I created a vector of structs which holds information such as size, location and if it is free or not.

The problem is when i call push_back it attempts to use my overloaded new function. This is where it fails because it can't use my overloaded new until it has pushed back the first structure of information.

Does anyone know how i can resolve this or a better way to keep track of the memory?

Upvotes: 1

Views: 1188

Answers (3)

Hicham
Hicham

Reputation: 979

create a class and overload new only in this class. you will not have problems with your vector. you will be able to use your own new with ::new A and the normal new with new A

class C
{
public:
void* operator new( size_t n ) ;
// ...
} ;

otherwise, you can use your own operator function rather than overload operator new :

a basic idea of an allocator :

int *i = myGetMem(i); // and myGetMem() allocates sizeof(*i) bytes of memory.

so you will not have problems with using the vector.

in fact, a real memory allocator keeps the information you put on the vector in the memory allocated it self :

you can take an algorithm for getmem/freemem to adapt it to your case. it can be helpfull.

e.g. : i want to allocate 10 bytes, the memory at @1024 contain information about memory allocated and the allocator returns an adress after 1024, maybe @1030 (depending of the information stored) as the start of allocated memory. so the user gets adress 1030 and he has memory between 1030 and 103A.

when calling the deallocator, the information at the beginning is used to correctly free the memory and to put it back in the list of avaible memory.

(the list of availvle memory is stored in popular alorithms in an array of linked lists of free memories organized by size with algorithms to avoid and minimize fragmentation)

this can resolve your need to the vector.

Upvotes: 1

Filip Roséen
Filip Roséen

Reputation: 63797

Don't overload global operator new!

The easiest and (WARNING; subjective ->) best solution would be to define your own Allocator which you'll use when dealing with allocation on the free-store (aka. heap). All STL containers have support for passing an AllocatorType as a template argument.

Overloading global operator new/operator delete might seem like a neat solution, but I can almost guarantee you that it will cause you troubles as the developing goes by.

Inside this custom made allocator you can keep track of what goes where, but make the internal std::vector (or whatever you'd like to use, a std::map seems more fitting to me) will use the default operator new/operator delete.

How do I create my own allocator?

The link below will lead you to a nice document with information regarding this matter:

Using a custom allocator when required/wanted will make you not run into any chicken and egg problem when trying to allocate memory for the allocator that will allocate memory, but the allocator must have allocated memory to use the allocator methods.. and what will allocate memory for the allocator but the allocator? Well we will need to allocate memory for that allocator and that allocator must have it's own allocator, though that allocator need memory, provided by another allocator?

Maybe I should just get myself a dog instead, they don't lay eggs - right?

Upvotes: 2

Krizz
Krizz

Reputation: 11552

You can create a vector using any custom allocator.

It is declared in the following manner:

std::vector<YourStruct, YourOwnAllocator> memory_allocations;

YourOwnAllocator is going to be a class which will allocate the data needed for the vector bypassing your overloaded operators. In needs to provide all the methods and typedefs listed here.

Upvotes: 0

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