connection rate improvement when using a half-open connections limit

include/libtorrent/connection_queue.hpp

@@ -40,6 +40,10 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/socket.hpp"
 #include "libtorrent/time.hpp"
 
+#ifdef TORRENT_CONNECTION_LOGGING
+#include <fstream>
+#endif
+
 namespace libtorrent
 {
 
@@ -48,7 +52,9 @@ class connection_queue : public boost::noncopyable
 public:
 	connection_queue(io_service& ios);
 
-	bool free_slots() const;
+	// if there are no free slots, returns the negative
+	// number of queued up connections
+	int free_slots() const;
 
 	void enqueue(boost::function<void(int)> const& on_connect
 		, boost::function<void()> const& on_timeout
@@ -59,9 +65,7 @@ public:
 	void close();
 
 #ifndef NDEBUG
-
 	void check_invariant() const;
-
 #endif
 
 private:
@@ -98,6 +102,9 @@ private:
 #ifndef NDEBUG
 	bool m_in_timeout_function;
 #endif
+#ifdef TORRENT_CONNECTION_LOGGING
+	std::ofstream m_log;
+#endif
 };
 
 }

src/connection_queue.cpp

@@ -45,10 +45,18 @@ namespace libtorrent
 #ifndef NDEBUG
 		, m_in_timeout_function(false)
 #endif
-	{}
+	{
+#ifdef TORRENT_CONNECTION_LOGGING
+		m_log.open("connection_queue.log");
+#endif
+	}
 
-	bool connection_queue::free_slots() const
-	{ return m_num_connecting < m_half_open_limit || m_half_open_limit <= 0; }
+	int connection_queue::free_slots() const
+	{
+		mutex_t::scoped_lock l(m_mutex);
+		return m_half_open_limit == 0 ? std::numeric_limits<int>::max()
+			: m_half_open_limit - m_queue.size();
+	}
 
 	void connection_queue::enqueue(boost::function<void(int)> const& on_connect
 		, boost::function<void()> const& on_timeout
@@ -109,7 +117,10 @@ namespace libtorrent
 	}
 
 	void connection_queue::limit(int limit)
-	{ m_half_open_limit = limit; }
+	{
+		TORRENT_ASSERT(limit >= 0);
+		m_half_open_limit = limit;
+	}
 
 	int connection_queue::limit() const
 	{ return m_half_open_limit; }
@@ -133,8 +144,11 @@ namespace libtorrent
 	{
 		INVARIANT_CHECK;
 
-		if (!free_slots())
-			return;
+#ifdef TORRENT_CONNECTION_LOGGING
+		m_log << log_time() << " " << free_slots() << std::endl;
+#endif
+
+		if (m_num_connecting >= m_half_open_limit) return;
 	
 		if (m_queue.empty())
 		{
@@ -171,7 +185,11 @@ namespace libtorrent
 			} catch (std::exception&) {}
 #endif
 
-			if (!free_slots()) break;
+#ifdef TORRENT_CONNECTION_LOGGING
+			m_log << log_time() << " " << free_slots() << std::endl;
+#endif
+
+			if (m_num_connecting >= m_half_open_limit) break;
 			i = std::find_if(i, m_queue.end(), boost::bind(&entry::connecting, _1) == false);
 		}
 	}

src/peer_connection.cpp

@@ -2943,10 +2943,16 @@ namespace libtorrent
 
 		m_connection_ticket = ticket;
 		boost::shared_ptr<torrent> t = m_torrent.lock();
-		TORRENT_ASSERT(t);
 
 		m_queued = false;
 		TORRENT_ASSERT(m_connecting);
+
+		if (!t)
+		{
+			disconnect("torrent aborted");
+			return;
+		}
+
 		m_socket->open(t->get_interface().protocol(), ec);
 		if (ec)
 		{

src/session_impl.cpp

@@ -844,8 +844,9 @@ namespace aux {
 		// round robin fashion, so that every torrent is
 		// equallt likely to connect to a peer
 
+		int free_slots = m_half_open.free_slots();
 		if (!m_torrents.empty()
-			&& m_half_open.free_slots()
+			&& free_slots > -m_half_open.limit()
 			&& num_connections() < m_max_connections)
 		{
 			// this is the maximum number of connections we will
@@ -869,6 +870,7 @@ namespace aux {
 						if (t.try_connect_peer())
 						{
 							--max_connections;
+							--free_slots;
 							steps_since_last_connect = 0;
 						}
 					}
@@ -894,7 +896,7 @@ namespace aux {
 				// handing out a single connection, break
 				if (steps_since_last_connect > num_torrents) break;
 				// if there are no more free connection slots, abort
-				if (m_half_open.free_slots() == 0) break;
+				if (free_slots <= -m_half_open.limit()) break;
 				// if we should not make any more connections
 				// attempts this tick, abort
 				if (max_connections == 0) break;

src/torrent.cpp

@@ -2469,7 +2469,6 @@ namespace libtorrent
 	bool torrent::want_more_peers() const
 	{
 		return int(m_connections.size()) < m_max_connections
-			&& m_ses.m_half_open.free_slots()
 			&& !m_paused
 			&& m_state != torrent_status::checking_files
 			&& m_state != torrent_status::queued_for_checking;