Tribblix: manual page: CURLMOPT_MAX_HOST

CURLMOPT_MAX_HOST_CONNECTIONS(3) Introduction to Library Functions

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

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

curl_multi_setopt(3) returns a CURLMcode indicating success or error.

CURLM_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).