Section: curl_multi_setopt options (3)
Updated: March 17, 2021
CURLMOPT_MAX_HOST_CONNECTIONS - set max number of connections to a single host
CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_MAX_HOST_CONNECTIONS, long max);
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
. When the limit is reached, the
sessions will be pending until a connection becomes available. If
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.
CURLM *m = curl_multi_init();
/* do no more than 2 connections per host */
curl_multi_setopt(m, CURLMOPT_MAX_HOST_CONNECTIONS, 2L);
Added in 7.30.0
Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.