CURLcode curl_easy_perform(CURL *handle);
You can do any amount of calls to curl_easy_perform(3) while using the same handle. If you intend to transfer more than one file, you are even encouraged to do so. libcurl will then attempt to re-use the same connection for the following transfers, thus making the operations faster, less CPU intense and using less network resources. Just note that you will have to use curl_easy_setopt(3) between the invokes to set options for the following curl_easy_perform.
You must never call this function simultaneously from two places using the same handle. Let the function return first before invoking it another time. If you want parallel transfers, you must use several curl handles.