mempool.c #1

#include <stdio.h>
#include <stdlib.h>
#include "mempool.h"

#define MEMPOOL_CHUNKSIZE (1024 * 128)

typedef struct _MEMPOOL_FREE_BLOCK {
    struct _MEMPOOL_FREE_BLOCK* next;
} MEMPOOL_FREE_BLOCK;

typedef struct _MEMPOOL {
    size_t item_size;
    long* alloc_count;
    MEMPOOL_FREE_BLOCK* free_list;
};

static MEMPOOL_FREE_BLOCK*
mempool_alloc_chunk(MEMPOOL* pool)
{
    MEMPOOL_FREE_BLOCK* chunk;
    MEMPOOL_FREE_BLOCK* p;
    MEMPOOL_FREE_BLOCK* end;
    long num_items;
    size_t chunk_size;
    size_t item_size;

    item_size = pool->item_size;
    num_items = MEMPOOL_CHUNKSIZE / item_size;
    chunk_size = num_items * item_size;

    if (pool->alloc_count) {
	++(*pool->alloc_count);
    }

    chunk = malloc(chunk_size);
    p = chunk;
    end = (MEMPOOL_FREE_BLOCK*)((char*)chunk + chunk_size);
    while (1) {
	MEMPOOL_FREE_BLOCK* next = (MEMPOOL_FREE_BLOCK*)((char*)p + item_size);
	if (next < end) {
	    p->next = next;
	} else {
	    p->next = NULL;
	    break;
	}
	p = next;
    }
    return chunk;
}


MEMPOOL*
mempool_create(size_t item_size, long* alloc_count)
{
    MEMPOOL* pool = malloc(sizeof(MEMPOOL));
    pool->item_size = item_size;
    pool->free_list = NULL;
    pool->alloc_count = alloc_count;
    return pool;
}


void*
mempool_alloc(MEMPOOL* pool)
{
    MEMPOOL_FREE_BLOCK* block;

    if (!pool->free_list) {
	/* with an empty free list, we need more memory */
	pool->free_list = mempool_alloc_chunk(pool);
    }

    /* pull off the head of the free list */
    block = pool->free_list;
    pool->free_list = pool->free_list->next;
    return block;
}


void
mempool_free(MEMPOOL* pool, void* item)
{
    if (item) {
	MEMPOOL_FREE_BLOCK* block;

	/* put this block on the head of the free list */
	block = (MEMPOOL_FREE_BLOCK*)item;
	block->next = pool->free_list;
	pool->free_list = block;
    }
}