curl / libcurl / API / curl_multi_setopt / CURLMOPT_MAX_TOTAL_CONNECTIONS

CURLMOPT_MAX_TOTAL_CONNECTIONS explained

Name

CURLMOPT_MAX_TOTAL_CONNECTIONS - max simultaneously open connections

Synopsis

#include <curl/curl.h>
 
CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_MAX_TOTAL_CONNECTIONS,
                            long amount);

Description

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. If CURLMOPT_PIPELINING 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.

While a transfer is queued up internally waiting for a connection, the CURLOPT_TIMEOUT_MS timeout is counted inclusive of the waiting time, meaning that if you set a too narrow timeout the transfer might never even start before it times out. The CURLOPT_CONNECTTIMEOUT_MS time is also similarly still treated as a per-connect timeout and might expire even before making a new connection is permitted.

Changing this value while there are transfers in progress is possible. The new value is then used the next time checks are performed. Lowering the value does not close down any active transfers, it simply does not allow new ones to get made.

Default

0, which means that there is no limit. It is then simply controlled by the number of easy handles added concurrently and how much multiplexing is being done.

Protocols

This functionality affects all supported protocols

Example

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

Availability

Added in curl 7.30.0

Return value

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