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I want to implement my own dynamic memory management system in order to add new features that help to manage memory in C++.
I use Windows (XP) and Linux (Ubuntu). What is needed to implement functions like 'malloc' and 'free'? I think that I have to use lowest level system calls.
For Windows, I have found the functions: GetProcessHeap, HeapAlloc, HeapCreate, HeapDestroy and HeapFree.
For Linux, I have not found any system calls for heap management. On Linux, malloc and free are system calls, are not they?
Thanks
Edit:
C++ does not provide garbage collector and garbage collector is slow. Some allocations are easy to free, but there are allocations that needs a garbage collector.
I want to implement these functions and add new features:
* Whenever free() be called, check if the pointer belongs to heap.
* Help with garbage collection. I have to store some information about the allocated block.
* Use multiple heaps (HeapCreate/HeapDestroy on Windows). I can delete an entire heap with its allocated blocks quickly.
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malloc go through each block, from start to end, until one freed block has enought space. If no block was available, append the block to the end of the last heap . If the last heap has not enought available space, the algorithm creates a new heap by calling mmap.
How malloc() and free() works depends on the runtime library used. Generally, malloc() allocates a heap (a block of memory) from the operating system. Each request to malloc() then allocates a small chunk of this memory be returning a pointer to the caller.
When one calls malloc , memory is taken from the large heap cell, which is returned by malloc . The rest is formed into a new heap cell that consists of all the rest of the memory. When one frees memory, the heap cell is added to the end of the heap's free list.
The malloc implementation in the GNU C Library is derived from ptmalloc (pthreads malloc), which in turn is derived from dlmalloc (Doug Lea malloc). This malloc may allocate memory in two different ways depending on their size and certain parameters that may be controlled by users.
On linux, malloc and free are not system calls. malloc/free obtains memory from the kernel by extending and shrinking(if it can) the data segment using the brk system calls as well as obtaining anonymous memory with mmap - and malloc manages memory within those regions. Some basic information any many great references can be found here
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In *nix, malloc() is implemented at the C library level. It uses brk()/sbrk() to grow/shrink the data segment, and mmap/munmap to request/release memory mappings. See this page for a description of the malloc implementation used in glibc and uClibc.
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