漫话Redis源码之一

今天看了下redis源码，记录一下ztrymalloc_usable

/* Try allocating memory, and return NULL if failed.
 * '*usable' is set to the usable size if non NULL. */
void *ztrymalloc_usable(size_t size, size_t *usable) {
    ASSERT_NO_SIZE_OVERFLOW(size);
    void *ptr = malloc(MALLOC_MIN_SIZE(size)+PREFIX_SIZE);
 
    if (!ptr) return NULL;
#ifdef HAVE_MALLOC_SIZE
    size = zmalloc_size(ptr);
    update_zmalloc_stat_alloc(size);
    if (usable) *usable = size;
    return ptr;
#else
    *((size_t*)ptr) = size;
    update_zmalloc_stat_alloc(size+PREFIX_SIZE);
    if (usable) *usable = size;
    return (char*)ptr+PREFIX_SIZE;
#endif
}