Ubuntu Manpage: CURLMOPT_MAX_HOST_CONNECTIONS - max number of connections to a single host

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 set number will be used as the maximum amount of
simultaneously open connections to a single host (a host being the same as a host name +
port number pair). For each new session to a host, libcurl will open a new connection up
to the limit set by CURLMOPT_MAX_HOST_CONNECTIONS(3). When the limit is reached, the
sessions will be pending until a connection becomes available. If CURLMOPT_PIPELINING(3)
is enabled, libcurl will try to pipeline if the host is capable of it.

The default max value is 0, unlimited. However, for backwards compatibility, setting it
to 0 when CURLMOPT_PIPELINING(3) is 1 will not be treated as unlimited. Instead it will
open only 1 connection and try to pipeline on it.

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 will be queued up waiting for their chance. When that happens, the
CURLOPT_TIMEOUT_MS(3) timeout will be 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.

DEFAULT

PROTOCOLS

       HTTP(S)

EXAMPLE

       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 7.30.0

RETURN VALUE

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