CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_MAXCONNECTS, long max);
DESCRIPTIONPass a long indicating the max. The set number will be used as the maximum amount of simultaneously open connections that libcurl may keep in its connection cache after completed use. By default libcurl will enlarge the size for each added easy handle to make it fit 4 times the number of added easy handles.
By setting this option, you can prevent the cache size from growing beyond the limit set by you.
When the cache is full, curl closes the oldest one in the cache to prevent the number of open connections from increasing.
This option is for the multi handle's use only, when using the easy interface you should instead use the CURLOPT_MAXCONNECTS(3) option.
See CURLMOPT_MAX_TOTAL_CONNECTIONS(3) for limiting the number of active connections.