curl_share_init man page
curl_share_init — Create a shared object
CURLSH *curl_share_init( );
This function returns a CURLSH handle to be used as input to all the other share-functions, sometimes referred to as a share handle in some places in the documentation. This init call MUST have a corresponding call to curl_share_cleanup when all operations using the share are complete.
This share handle is what you pass to curl using the CURLOPT_SHARE(3) option with curl_easy_setopt(3), to make that specific curl handle use the data in this share.
If this function returns NULL, something went wrong (out of memory, etc.) and therefore the share object was not created.
CURLOPT_DNS_USE_GLOBAL_CACHE(3), CURLOPT_SHARE(3), curl_share_cleanup(3), curl_share_setopt(3), libcurl-share(3).