CURLMOPT_MAX_TOTAL_CONNECTIONS - Man Page

#include <curl/curl.h>

CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_MAX_TOTAL_CONNECTIONS,
                            long amount);

Pass a long for the amount. The set number is used as the maximum number of simultaneously open connections in total using this multi handle. For each new session, libcurl might open a new connection up to the limit set by CURLMOPT_MAX_TOTAL_CONNECTIONS(3). When the limit is reached, new sessions are held pending until there are available connections. If CURLMOPT_PIPELINING(3) is enabled, libcurl can try multiplexing if the host is capable of it.

When more transfers are added to the multi handle than what can be performed due to the set limit, they get queued up waiting for their chance. When that happens, the CURLOPT_TIMEOUT_MS(3) timeout is counted inclusive of the waiting time, meaning that if you set a too narrow timeout in such a case the transfer might never even start before it times out.

Even in the queued up situation, the CURLOPT_CONNECTTIMEOUT_MS(3) timeout is however treated as a per-connect timeout.

0, which means that there is no limit. It is then simply controlled by the number of easy handles added.

This functionality affects all supported protocols

int main(void)
{
  CURLM *m = curl_multi_init();
  /* never do more than 15 connections */
  curl_multi_setopt(m, CURLMOPT_MAX_TOTAL_CONNECTIONS, 15L);
}

Added in curl 7.30.0

Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.

CURLMOPT_MAXCONNECTS(3), CURLMOPT_MAX_HOST_CONNECTIONS(3)

CURLMOPT_MAXCONNECTS(3), CURLMOPT_MAX_HOST_CONNECTIONS(3), curl_multi_setopt(3), CURLOPT_MAXCONNECTS(3), libcurl-symbols(3), nbdkit-curl-plugin(1).