added smooth_connect and turned it on by default

docs/manual.rst

@@ -4304,6 +4304,7 @@ session_settings
 		bool no_connect_privileged_ports;
 		int alert_queue_size;
 		int max_metadata_size;
+		bool smooth_connects;
 	};
 
 ``version`` is automatically set to the libtorrent version you're using
@@ -5137,6 +5138,12 @@ defaults to 1000.
 ``max_metadata_size`` is the maximum allowed size (in bytes) to be received
 by the metadata extension, i.e. magnet links. It defaults to 1 MiB.
 
+``smooth_connects`` is true by default, which means the number of connection
+attempts per second may be limited to below the ``connection_speed``, in case
+we're close to bump up against the limit of number of connections. The intention
+of this setting is to more evenly distribute our connection attempts over time,
+instead of attempting to connectin in batches, and timing them out in batches.
+
 pe_settings
 ===========
 

include/libtorrent/session_settings.hpp

@@ -263,6 +263,7 @@ namespace libtorrent
 			, no_connect_privileged_ports(true)
 			, alert_queue_size(1000)
 			, max_metadata_size(1024*1024)
+			, smooth_connects(true)
 		{}
 
 		// libtorrent version. Used for forward binary compatibility
@@ -1046,6 +1047,10 @@ namespace libtorrent
 		// the max allowed size for metadata received by the
 		// ut_metadata extension (i.e. magnet links)
 		int max_metadata_size;
+
+		// attempt to smooth out connects to avoid getting spikes in
+		// opening connections and timing out connections
+		bool smooth_connects;
 	};
 
 #ifndef TORRENT_DISABLE_DHT

src/session_impl.cpp

@@ -358,6 +358,7 @@ namespace aux {
 		TORRENT_SETTING(boolean, no_connect_privileged_ports)
 		TORRENT_SETTING(integer, alert_queue_size)
 		TORRENT_SETTING(integer, max_metadata_size)
+		TORRENT_SETTING(integer, smooth_connects)
 	};
 
 #undef TORRENT_SETTING
@@ -3020,6 +3021,13 @@ namespace aux {
 			}
 		}
 
+		// this logic is here to smooth out the number of new connection
+		// attempts over time, to prevent connecting a large number of
+		// sockets, wait 10 seconds, and then try again
+		int limit = (std::min)(m_settings.connections_limit - num_connections(), free_slots);
+		if (m_settings.smooth_connects && max_connections > (limit+1) / 2)
+			max_connections = (limit+1) / 2;
+
 		if (!m_torrents.empty()
 			&& free_slots > -m_half_open.limit()
 			&& num_connections() < m_settings.connections_limit