ASYNC_WAIT_CTX_get_callback
if (ASYNC_WAIT_CTX_get_callback(waitctx, &callback, &callback_arg) && callback != NULL) {
int ASYNC_WAIT_CTX_get_callback(ASYNC_WAIT_CTX *ctx,
|| ASYNC_WAIT_CTX_get_callback(waitctx, &get_callback, &get_arg)