don't let hung outgoing connection attempts block incoming connections

ChangeLog

@@ -1,3 +1,4 @@
+	* don't let hung outgoing connection attempts block incoming connections
 	* improve SSL torrent support by using SNI and a single SSL listen socket
 	* improved peer exchange performance by sharing incoming connections which advertize listen port 
 	* deprecate set_ratio(), and per-peer rate limits

include/libtorrent/peer_connection.hpp

@@ -1164,7 +1164,7 @@ namespace libtorrent
 		// buffer messages up in the application layer send
 		// buffer, and send it once we're uncorked.
 		bool m_corked:1;
-		
+
 		template <std::size_t Size>
 		struct handler_storage
 		{

include/libtorrent/torrent.hpp

@@ -955,6 +955,12 @@ namespace libtorrent
 	public:
 #endif
 		std::set<peer_connection*> m_connections;
+		// of all peers in m_connections, this is the number
+		// of peers that are outgoing and still waiting to
+		// complete the connection. This is used to possibly
+		// kick out these connections when we get incoming
+		// connections (if we've reached the connection limit)
+		int m_num_connecting;
 #ifdef TORRENT_DEBUG
 	private:
 #endif

src/peer_connection.cpp

@@ -200,6 +200,14 @@ namespace libtorrent
 		, m_received_in_piece(0)
 #endif
 	{
+		boost::shared_ptr<torrent> t = m_torrent.lock();
+		// if t is NULL, we better not be connecting, since
+		// we can't decrement the connecting counter
+		TORRENT_ASSERT(t || !m_connecting);
+		if (m_connecting && t)
+		{
+			++t->m_num_connecting;
+		}
 		m_est_reciprocation_rate = m_ses.m_settings.default_est_reciprocation_rate;
 
 #if TORRENT_USE_I2P
@@ -347,6 +355,14 @@ namespace libtorrent
 		, m_received_in_piece(0)
 #endif
 	{
+		boost::shared_ptr<torrent> t = m_torrent.lock();
+		// if t is NULL, we better not be connecting, since
+		// we can't decrement the connecting counter
+		TORRENT_ASSERT(t || !m_connecting);
+		if (m_connecting && t)
+		{
+			++t->m_num_connecting;
+		}
 		m_est_reciprocation_rate = m_ses.m_settings.default_est_reciprocation_rate;
 
 #if TORRENT_USE_I2P
@@ -910,6 +926,22 @@ namespace libtorrent
 		TORRENT_ASSERT(m_disconnecting);
 		TORRENT_ASSERT(m_disconnect_started);
 
+		// defensive
+
+		boost::shared_ptr<torrent> t = m_torrent.lock();
+		// if t is NULL, we better not be connecting, since
+		// we can't decrement the connecting counter
+		TORRENT_ASSERT(t || !m_connecting);
+
+		// we should really have dealt with this already
+		TORRENT_ASSERT(!m_connecting);
+		if (m_connecting && t)
+		{
+			TORRENT_ASSERT(t->m_num_connecting > 0);
+			--t->m_num_connecting;
+			m_connecting = false;
+		}
+
 		m_disk_recv_buffer_size = 0;
 
 #ifndef TORRENT_DISABLE_EXTENSIONS
@@ -928,8 +960,6 @@ namespace libtorrent
 			TORRENT_ASSERT(!i->second->has_peer(this));
 		if (m_peer_info)
 			TORRENT_ASSERT(m_peer_info->connection == 0);
-
-		boost::shared_ptr<torrent> t = m_torrent.lock();
 #endif
 	}
 
@@ -3396,10 +3426,17 @@ namespace libtorrent
 
 		TORRENT_ASSERT(m_connecting);
 
+		boost::shared_ptr<torrent> t = m_torrent.lock();
+		if (m_connecting)
+		{
+			TORRENT_ASSERT(t->m_num_connecting > 0);
+			--t->m_num_connecting;
+			m_connecting = false;
+		}
+
 		if (m_connection_ticket != -1)
 		{
 			m_ses.m_half_open.done(m_connection_ticket);
-			m_connecting = false;
 		}
 
 		// a connection attempt using uTP just failed
@@ -3523,13 +3560,19 @@ namespace libtorrent
 			m_channel_state[download_channel] &= ~peer_info::bw_disk;
 		}
 
-		if (m_connecting && m_connection_ticket >= 0)
+		boost::shared_ptr<torrent> t = m_torrent.lock();
+		if (m_connecting)
+		{
+			TORRENT_ASSERT(t->m_num_connecting > 0);
+			--t->m_num_connecting;
+			m_connecting = false;
+		}
+		if (m_connection_ticket >= 0)
 		{
 			m_ses.m_half_open.done(m_connection_ticket);
 			m_connection_ticket = -1;
 		}
 
-		boost::shared_ptr<torrent> t = m_torrent.lock();
 		torrent_handle handle;
 		if (t) handle = t->get_handle();
 
@@ -4052,7 +4095,14 @@ namespace libtorrent
 		if (!t || m_disconnecting)
 		{
 			m_ses.m_half_open.done(m_connection_ticket);
-			m_connecting = false;
+			if (m_connection_ticket >= -1) m_connection_ticket = -1;
+			TORRENT_ASSERT(t || !m_connecting);
+			if (m_connecting && t)
+			{
+				TORRENT_ASSERT(t->m_num_connecting > 0);
+				--t->m_num_connecting;
+				m_connecting = false;
+			}
 			disconnect(errors::torrent_aborted);
 			return;
 		}
@@ -5427,7 +5477,16 @@ namespace libtorrent
 			return;
 		}
 
-		m_connecting = false;
+		// if t is NULL, we better not be connecting, since
+		// we can't decrement the connecting counter
+		boost::shared_ptr<torrent> t = m_torrent.lock();
+		TORRENT_ASSERT(t || !m_connecting);
+		if (m_connecting && t)
+		{
+			TORRENT_ASSERT(t->m_num_connecting > 0);
+			--t->m_num_connecting;
+			m_connecting = false;
+		}
 		m_ses.m_half_open.done(m_connection_ticket);
 
 		if (m_disconnecting) return;
@@ -5469,7 +5528,6 @@ namespace libtorrent
 		{
 			// if the remote endpoint is the same as the local endpoint, we're connected
 			// to ourselves
-			boost::shared_ptr<torrent> t = m_torrent.lock();
 			if (m_peer_info && t) t->get_policy().ban_peer(m_peer_info);
 			disconnect(errors::self_connection, 1);
 			return;

src/torrent.cpp

@@ -352,6 +352,7 @@ namespace libtorrent
 		, m_total_downloaded(0)
 		, m_started(time_now())
 		, m_storage(0)
+		, m_num_connecting(0)
 		, m_tracker_timer(ses.m_io_service)
 		, m_ses(ses)
 		, m_trackerid(p.trackerid)
@@ -5649,8 +5650,27 @@ namespace libtorrent
 
 		if (m_connections.size() >= m_max_connections)
 		{
-			p->disconnect(errors::too_many_connections);
-			return false;
+			// if more than 10% of the connections are outgoing
+			// connection attempts that haven't completed yet,
+			// disconnect one of them and let this incoming
+			// connection through.
+			if (m_num_connecting < m_max_connections / 10)
+			{
+				p->disconnect(errors::too_many_connections);
+				return false;
+			}
+
+			// find one of the connecting peers and disconnect it
+			// TODO: ideally, we would disconnect the oldest connection
+			// i.e. the one that has waited the longest to connect.
+			for (std::set<peer_connection*>::iterator i = m_connections.begin()
+				, end(m_connections.end()); i != end; ++i)
+			{
+				peer_connection* p = *i;
+				if (!p->is_connecting()) continue;
+				p->disconnect(errors::too_many_connections);
+				break;
+			}
 		}
 
 		TORRENT_TRY