CURLOPT_MAXCONNECTS man page
CURLOPT_MAXCONNECTS — maximum connection cache size
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_MAXCONNECTS, long amount);
Pass a long. The set amount will be the maximum number of simultaneously open persistent connections that libcurl may cache in the pool associated with this handle. The default is 5, and there isn't much point in changing this value unless you are perfectly aware of how this works and changes libcurl's behaviour. This concerns connections using any of the protocols that support persistent connections.
When reaching the maximum limit, curl closes the oldest one in the cache to prevent increasing the number of open connections.
If you already have performed transfers with this curl handle, setting a smaller CURLOPT_MAXCONNECTS(3) than before may cause open connections to get closed unnecessarily.
If you add this easy handle to a multi handle, this setting is not acknowledged, and you must instead use curl_multi_setopt(3) and the CURLMOPT_MAXCONNECTS(3) option.
curl_easy_setopt(3), CURLMOPT_MAXCONNECTS(3), CURLOPT_FORBID_REUSE(3), libcurl-tutorial(3).