atexit implementation

stdlib.c

/**
 * Standard requires atleast 32, but except
 * for this upper bound the limit is implementation
 * defined.
 */
#define ATEXIT_HANDLER_LIMIT 32

typedef void (*atexit_handler_t)(void);

static atexit_handler_t static_handlers[ATEXIT_HANDLER_LIMIT];
static size_t static_handler_count = 0;

static atexit_handler_t *dynamic_handlers = NULL;
static size_t dynamic_handler_size = ATEXIT_HANDLER_LIMIT;
static size_t dynamic_handler_count = 0;

int atexit(atexit_handler_t handler)
{
	if (!handler)
		return -1;

	if (static_handler_count < ATEXIT_HANDLER_LIMIT)
		static_handlers[static_handler_count++] = handler;
	else {
		if (dynamic_handler_count == 0 ||
		    dynamic_handler_count >= dynamic_handler_size) {
			dynamic_handler_size *= 2;
			atexit_handler_t *new_handlers = realloc(
				dynamic_handlers,
				dynamic_handler_size * sizeof(atexit_handler_t)
			);

			if (!new_handlers)
				return -1;
			else
				dynamic_handlers = new_handlers;
		}

		dynamic_handlers[dynamic_handler_count++] = handler;
	}

	return 0;
}

/**
 * To silence GCC warning about a missing prototype.
 */
void call_atexit_handlers(void);

void call_atexit_handlers(void)
{
	for (size_t i = dynamic_handler_count; i > 0; --i)
		dynamic_handlers[i - 1]();
	free(dynamic_handlers);
	dynamic_handler_count = 0;
	dynamic_handler_size = ATEXIT_HANDLER_LIMIT;

	for (size_t i = static_handler_count; i > 0; --i)
		static_handlers[i - 1]();
}