slab.c

/* Trivial (and totally untested) slab allocator */

struct slab;
struct slab {
    struct slab *prev;
    void *buf;
    size_t avail, orig_size;
};

struct slab *slab_create(size_t initial_size) {
    /* XXX: check for overflow in addition */
    struct slab *slab = malloc(initial_size + sizeof(struct slab));
    slab->prev = 0;
    slab->buf = slab + 1;
    slab->avail = initial_size;
    slab->orig_size = initial_size;
}

void *slab_alloc(struct slab *slab, size_t bytes) {
    if (bytes > slab->avail) {
        size_t new_size = slab->orig_size;
        if (bytes > new_size) {
            new_size = bytes;
        }
        /* XXX: check for overflow in addition */
        struct slab *new_slab = malloc(new_size + sizeof(struct slab));
        new_slab->prev = slab;
        new_slab->buf = new_slab + 1;
        new_slab->avail = new_size;
        new_slab->orig_size = new_size;
        slab = new_slab;
    }
    {
        void *p = slab->buf;
        /* XXX: round up bytes for alignment of next allocation (but
         * ensuring that slab->avail won't go negative) */
        slab->buf += bytes;
        slab->avail -= bytes;
        return p;
    }
}

void slab_destroy(struct slab *slab) {
    if (slab->prev) {
        slab_destroy(slab->prev);
    }
    free(slab);
}