CURLMOPT_MAX_HOST_CONNECTIONS(3)

NAME
CURLMOPT_MAX_HOST_CONNECTIONS - max number of connections to a single host

SYNOPSIS
#include <curl/curl.h>

CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_MAX_HOST_CONNECTIONS,
                            long max);

DESCRIPTION
Pass a long to indicate max, the maximum amount of simultaneously open connections libcurl may hold a single host (a host being the same as a hostname + port number pair). For each new transfer to the same host, libcurl might open a new connection up to the limit set by CURLMOPT_MAX_HOST_CONNECTIONS(3). When the limit is reached, new sessions are kept pending until a connection becomes available.

The default max value is 0, unlimited. This set limit is also used for proxy connections, and then the proxy is considered to be the host for which this limit counts.

When more transfers are added to the multi handle than what can be performed due to the set limit, they are queued up waiting for their chance.

While a transfer is queued up internally waiting for a connection, the CURLOPT_TIMEOUT_MS(3) 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(3) 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

PROTOCOLS
This functionality affects all supported protocols

EXAMPLE
int main(void)
{
  CURLM *m = curl_multi_init();
  /* do no more than 2 connections per host */
  curl_multi_setopt(m, CURLMOPT_MAX_HOST_CONNECTIONS, 2L);
}

AVAILABILITY
Added in curl 7.30.0

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

SEE ALSO
CURLMOPT_MAXCONNECTS(3), CURLMOPT_MAX_TOTAL_CONNECTIONS(3)