CURLcode curl_easy_setopt(CURL *handle, CURLOPT_MAXAGE_CONN, long maxage);
The "connection cache" that holds previously used connections. When a new request is to be done, it will consider any connection that matches for reuse. The CURLOPT_MAXAGE_CONN(3) limit prevents libcurl from trying very old connections for reuse, since old connections have a high risk of not working and thus trying them is a performance loss and sometimes service loss due to the difficulties to figure out the situation. If a connection is found in the cache that is older than this set maxage, it will instead be closed.
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
/* only allow 30 seconds idle time */
curl_easy_setopt(curl, CURLOPT_MAXAGE_CONN, 30L);
curl_easy_perform(curl);
}