Change CURLMOPT_MAX_TOTAL_CONNECTIONS and CURLMOPT_MAX_HOST_CONNECTIONS options

[pkropachev]

Hello!

In documentation for options CURLMOPT_MAX_HOST_CONNECTIONS and CURLMOPT_MAX_TOTAL_CONNECTIONS nothing say about ability to change these options while the life of curl multi handle (CURLM).
Could you please clarify if it's possible to change these options during the life of CURLM? If so, how will new values be applied? For example initial value for CURLMOPT_MAX_HOST_CONNECTIONS was 10, then it's changed to 5. Will curl manage it by itself and narrow connections down?

Thanks!

[jay]

The code is not written for that. CURLMOPT_MAX_HOST_CONNECTIONS here is the logic:

curl/lib/url.c

Lines 3689 to 3717 in 5ce164e

	if(waitpipe)
	/* There is a connection that *might* become usable for multiplexing
	"soon", and we wait for that */
	connections_available = FALSE;
	else {
	/* this gets a lock on the conncache */
	struct connectbundle *bundle =
	Curl_conncache_find_bundle(data, conn, data->state.conn_cache);
	if(max_host_connections > 0 && bundle &&
	(bundle->num_connections >= max_host_connections)) {
	struct connectdata *conn_candidate;
	/* The bundle is full. Extract the oldest connection. */
	conn_candidate = Curl_conncache_extract_bundle(data, bundle);
	CONNCACHE_UNLOCK(data);
	if(conn_candidate)
	Curl_disconnect(data, conn_candidate, FALSE);
	else {
	infof(data, "No more connections allowed to host: %zu",
	max_host_connections);
	connections_available = FALSE;
	}
	}
	else
	CONNCACHE_UNLOCK(data);
	}

[pkropachev]

Thanks @jay!
Let's currently consider it like changes these options won't have any effect. I'll check with test application.

[bagder]

I would rather say that changes will have an effect. The next time the value is checked, it takes effect.

[pkropachev]

Thanks @bagder!
But for me still not clear how will curl decrease number of simultaneously connection, e.g. in case change it from 10 to 5?

[bagder]

It does nothing initially. The check is only done when deciding if a new connection can be setup, so if you already have 10 connections when you lower the max to 5, nothing will happen to your already setup connections. But if three of them finish and you want to create a new transfer, it cannot create a new connection anymore since it is now already maxed out.

[bagder]

Here is my attempt at clarifying this: #13176

[pkropachev]

Thanks Daniel!