git/mem-pool.c

/*
 * Memory Pool implementation logic.
 */

#include "cache.h"
#include "mem-pool.h"

#define BLOCK_GROWTH_SIZE 1024*1024 - sizeof(struct mp_block);

/*
 * Allocate a new mp_block and insert it after the block specified in
 * `insert_after`. If `insert_after` is NULL, then insert block at the
 * head of the linked list.
 */
static struct mp_block *mem_pool_alloc_block(struct mem_pool *mem_pool, size_t block_alloc, struct mp_block *insert_after)
{
	struct mp_block *p;

	mem_pool->pool_alloc += sizeof(struct mp_block) + block_alloc;
	p = xmalloc(st_add(sizeof(struct mp_block), block_alloc));

	p->next_free = (char *)p->space;
	p->end = p->next_free + block_alloc;

	if (insert_after) {
		p->next_block = insert_after->next_block;
		insert_after->next_block = p;
	} else {
		p->next_block = mem_pool->mp_block;
		mem_pool->mp_block = p;
	}

	return p;
}

void mem_pool_init(struct mem_pool **mem_pool, size_t initial_size)
{
	struct mem_pool *pool;

	if (*mem_pool)
		return;

	pool = xcalloc(1, sizeof(*pool));

	pool->block_alloc = BLOCK_GROWTH_SIZE;

	if (initial_size > 0)
		mem_pool_alloc_block(pool, initial_size, NULL);

	*mem_pool = pool;
}

void mem_pool_discard(struct mem_pool *mem_pool)
{
	struct mp_block *block, *block_to_free;

	while ((block = mem_pool->mp_block))
	{
		block_to_free = block;
		block = block->next_block;
		free(block_to_free);
	}

	free(mem_pool);
}

void *mem_pool_alloc(struct mem_pool *mem_pool, size_t len)
{
	struct mp_block *p = NULL;
	void *r;

	/* round up to a 'uintmax_t' alignment */
	if (len & (sizeof(uintmax_t) - 1))
		len += sizeof(uintmax_t) - (len & (sizeof(uintmax_t) - 1));

	if (mem_pool->mp_block &&
	    mem_pool->mp_block->end - mem_pool->mp_block->next_free >= len)
		p = mem_pool->mp_block;

	if (!p) {
		if (len >= (mem_pool->block_alloc / 2))
			return mem_pool_alloc_block(mem_pool, len, mem_pool->mp_block);

		p = mem_pool_alloc_block(mem_pool, mem_pool->block_alloc, NULL);
	}

	r = p->next_free;
	p->next_free += len;
	return r;
}

void *mem_pool_calloc(struct mem_pool *mem_pool, size_t count, size_t size)
{
	size_t len = st_mult(count, size);
	void *r = mem_pool_alloc(mem_pool, len);
	memset(r, 0, len);
	return r;
}