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mem.c
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mem.c
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#include <sys/mman.h>
#include <stdio.h>
#include <unistd.h>
#include "mem.h"
//to print out extra logs
int DEBUG = 0;
void *Mem_Init(int sizeOfRegion)
{
head_ptr = mmap(NULL, sizeOfRegion, PROT_READ| PROT_WRITE , MAP_PRIVATE | MAP_ANON , -1 , 0);
if(head_ptr == MAP_FAILED)
{
printf("Mem_Init(): mmap returned NULL.\n");
return NULL;
}
else
{
//at the start of memory I am storing ref to 3 listS(mem_chuncks(by mmap), free_list and alloc_list)
struct header **mem_chunck_list = (struct header **)head_ptr;
struct header **free_list = (struct header **)(head_ptr + sizeof(struct header **));
struct header **alloc_list = (struct header **)(head_ptr + 2*sizeof(struct header **));
//at this moment only one chuck
*mem_chunck_list = NULL;
//because nothing allocated yet
*alloc_list = NULL;
//creating first free block
struct header *first_free_block = head_ptr + 3*sizeof(struct header **);
first_free_block->size =sizeOfRegion-3*sizeof(struct header **)-sizeof(struct header);
first_free_block->next = NULL;
*free_list = first_free_block;
if(DEBUG)
printf("Mem_Init(): (mmap_chuncks): %p, (free_list): %p, (alloc_list): %p\n", *mem_chunck_list, *free_list, *alloc_list);
return head_ptr;
}
}
int Mem_Free(void *ptr, int coalesce, int release)
{
if(ptr == NULL)
return 0;
//getting references to the heads of three lists
struct header **mem_chunck_list = (struct header **)head_ptr;
struct header **free_list = (struct header **)(head_ptr + sizeof(struct header **));
struct header **alloc_list = (struct header **)(head_ptr + 2*sizeof(struct header **));
//getting the address where the header starts
struct header *block_to_free = ptr - sizeof(struct header);
//find the block in the list
struct header *cur = *alloc_list, *prev = *alloc_list;
while (cur && cur != block_to_free)
{
prev = cur;
cur = cur->next;
}
if(DEBUG)
printf("Mem_Free: Addr: %p, Size: %d, Next: %p, Cur: %p, Prev: %p\n", block_to_free, block_to_free->size, block_to_free->next, cur, prev);
if(cur)
{
//remove from allocated list
if(cur == prev) // if there is the first in the list
{
*alloc_list = cur->next;
}
else // if in the middle of the list
{
prev->next = cur->next;
}
//add block at the start of free block
cur->next = *free_list;
*free_list = cur;
if(DEBUG)
printf("Mem_Free: free_list(%p), alloc_list(%p)\n", *free_list, *alloc_list);
}
else
{
//cases when pointer is not assigned by Mem_Alloc()
printf("Mem_Free: Could not free memory, invalid pointer.\n");
return -1;
}
if(coalesce)
{
//because recently freed block is added to the front of the list
struct header *freed_block = *free_list;
//traverse the list and find if adjacents blocks are free to coalesce
struct header *cur_block = (*free_list)->next;
struct header *prev_block = *free_list;
int counter = 0;
while(cur_block)
{
//when block before freed block is free
if((void *)cur_block + sizeof(struct header) + cur_block->size == freed_block)
{
//ditching the recetly created freed block
*free_list = (*free_list)->next;
cur_block->size = freed_block->size + sizeof(struct header) +cur_block->size;
counter++;
if(counter==2)
break;
}
//when block after freed block is free
else if ((void *)freed_block + sizeof(struct header) + freed_block->size == cur_block)
{
//ditching the block after the freed block
prev_block->next = cur_block->next;
freed_block->size = cur_block->size + sizeof(struct header) + freed_block->size;
counter++;
if(counter == 2)
break;
}
prev_block = cur_block;
cur_block = cur_block->next;
}
}
if(release)
{
int _continue;
struct header *cur_chunck = *mem_chunck_list, *prev_chunck = *mem_chunck_list;
while(cur_chunck)
{
struct header *possible_free_block = (void *)cur_chunck + sizeof(struct header);
struct header *cur_free_block = *free_list, *prev_free_block=*free_list;
_continue = 0;
while (cur_free_block)
{
//check if the there is any free block which is entirely on the free_chunck
if(cur_free_block == possible_free_block && cur_free_block->size == cur_chunck->size-2*sizeof(struct header))
{
void *mem_to_unmap = cur_chunck;
int length = cur_chunck->size;
//ditching the free chunck from mem_chunck_list
if(cur_chunck == prev_chunck)
{
*mem_chunck_list = cur_chunck->next;
cur_chunck = *mem_chunck_list;
prev_chunck = *mem_chunck_list;
}
else
{
prev_chunck->next = cur_chunck->next;
cur_chunck=prev_chunck->next;
}
_continue = 1;
//ditching the free block from free_list
if(prev_free_block == cur_free_block)
{
*free_list = cur_free_block->next;
cur_free_block = *free_list;
prev_free_block = *free_list;
}
else
{
prev_free_block->next = cur_free_block->next;
cur_free_block = prev_free_block->next;
}
//unmapping the memory
munmap(mem_to_unmap, length);
}
else
{
prev_free_block=cur_free_block;
cur_free_block = cur_free_block->next;
}
}
if(_continue)
continue;
prev_chunck = cur_chunck;
cur_chunck = cur_chunck->next;
}
}
return 0;
}
void *Mem_Alloc(int size, int expand)
{
//if user request memory of size 0 or less
if(size <= 0)
return NULL;
struct header **mem_chunck_list;
struct header **free_list;
struct header **alloc_list;
retry_allocation:
//getting references of the lists
mem_chunck_list = (struct header **)head_ptr;
free_list = (struct header **)(head_ptr + sizeof(struct header **));
alloc_list = (struct header **)(head_ptr + 2*sizeof(struct header **));
struct header *next_free_block;
struct header *new_free_block;
struct header *prev_free_block;
struct header *cur_free_block;
//find the next suitable block by traversing the free list
cur_free_block = *free_list;
prev_free_block = *free_list;
while(cur_free_block && cur_free_block->next)
{
if (cur_free_block->size == size)
{
break;
}
else if(cur_free_block->size >= size + sizeof(struct header))
{
break;
}
else
{
prev_free_block = cur_free_block;
cur_free_block = cur_free_block->next;
}
}
if(cur_free_block && ((cur_free_block->size >= (size + sizeof(struct header))) || (cur_free_block->size == size)))
{
next_free_block = cur_free_block->next;
//if found block has excess memory than required
if(cur_free_block->size >= size + sizeof(struct header))
{
new_free_block = (struct header *) ((void *)cur_free_block + size + sizeof(struct header));
new_free_block->size = cur_free_block->size-size-sizeof(struct header);
new_free_block->next = next_free_block;
if(cur_free_block == prev_free_block) //means what we had only one block
{
*free_list = new_free_block;
}
else
{
prev_free_block->next = new_free_block;
}
}
else //found block has exactly the same memory
{
if(cur_free_block == prev_free_block)
{
*free_list = next_free_block;
}
else
{
prev_free_block->next = next_free_block;
}
}
//Now adding the given memory block to allocated-list
cur_free_block->size = size;
if(*alloc_list==NULL)
{
*alloc_list=cur_free_block;
cur_free_block->next = NULL;
}
else //adding new block to the front of the list
{
cur_free_block->next = *alloc_list;
*alloc_list = cur_free_block;
}
if(DEBUG)
{
printf("Mem_Alloc: Block Assigned: %p, Size: %d, Next: %p\n", cur_free_block, cur_free_block->size, cur_free_block->next);
printf("Mem_Alloc: free_list(%p), alloc_list(%p)\n", *free_list, *alloc_list);
}
return (void *)cur_free_block + sizeof(struct header);
}
else
{
if(expand)
{
//calculating the page aligned size for new memory allocation
int required_size = size + 2*sizeof(struct header);
int page_size = sysconf(_SC_PAGE_SIZE);
int new_mem_size = page_size + required_size;
int a = new_mem_size % page_size;
new_mem_size = new_mem_size - a;
void *new_chunck = mmap(NULL, new_mem_size, PROT_READ| PROT_WRITE , MAP_PRIVATE | MAP_ANON , -1 , 0);
struct header *chunck_header = new_chunck;
chunck_header->size = new_mem_size; //original chuck size as given by mmap() (excluding size of headers)
if(*mem_chunck_list == NULL) //means first extra chunck
{
chunck_header->next = NULL;
*mem_chunck_list = chunck_header;
}
else //already have extra chucks
{
chunck_header->next = *mem_chunck_list;
*mem_chunck_list = chunck_header;
}
//creating new free block on newly allocated chunck
struct header *new_free_block = new_chunck + sizeof(struct header);
new_free_block->size = new_mem_size - 2*sizeof(struct header);
new_free_block->next = *free_list;
*free_list = new_free_block;
//now that new memory is allocated, try allocating the memory again
goto retry_allocation;
}
else
{
printf("Mem_Alloc(expand=0): Cannot provide memory of %d bytes.\n", size);
return NULL;
}
}
}
void Mem_Dump()
{
struct header **mem_chunck_list = (struct header **)head_ptr;
struct header **free_list = (struct header **)(head_ptr+sizeof(struct header **));
struct header **alloc_list = (struct header **)(head_ptr + 2*sizeof(struct header **));
printf("----------Free List (head: %p)-------------", *free_list);
if(*free_list == NULL) printf("---------\n"); else printf("\n");
struct header *cur = *free_list;
while(cur)
{
printf("Address: %p, Size: %d, Next: %p\n", cur, cur->size, cur->next);
cur = cur->next;
}
printf("-------------------------------------------------------\n");
printf("-------Allocated List (head: %p)-----------", *alloc_list);
if(*alloc_list == NULL) printf("---------\n"); else printf("\n");
cur = *alloc_list;
while(cur)
{
printf("Address: %p, Size: %d, Next: %p\n", cur, cur->size, cur->next);
cur = cur->next;
}
printf("-------------------------------------------------------\n");
printf("--------Chunck List (head: %p)-------------", *mem_chunck_list);
if(*mem_chunck_list == NULL) printf("---------\n"); else printf("\n");
cur = *mem_chunck_list;
while(cur)
{
printf("Address: %p, Size: %d, Next: %p\n", cur, cur->size, cur->next);
cur = cur->next;
}
printf("-------------------------------------------------------\n");
}