cancel non-critical DNS lookups when shutting down, to cut down on shutdown delay

ChangeLog

@@ -1,3 +1,5 @@
+	* cancel non-critical DNS lookups when shutting down, to cut down on
+	  shutdown delay.
 	* greatly simplify the debug logging infrastructure. logs are now delivered
 	  as alerts, and log level is controlled by the alert mask.
 	* removed auto_expand_choker. use rate_based_choker instead

include/libtorrent/resolver.hpp

@@ -53,6 +53,8 @@ struct TORRENT_EXTRA_EXPORT resolver : resolver_interface
 	void async_resolve(std::string const& host, int flags
 		, callback_t const& h);
 
+	void abort();
+
 private:
 
 	void on_lookup(error_code const& ec, tcp::resolver::iterator i
@@ -67,8 +69,13 @@ private:
 	typedef boost::unordered_map<std::string, dns_cache_entry> cache_t;
 	cache_t m_cache;
 	io_service& m_ios;
+
+	// all lookups in this resolver are aborted on shutdown.
 	tcp::resolver m_resolver;
 
+	// lookups in this resolver are not aborted on shutdown
+	tcp::resolver m_critical_resolver;
+
 	// max number of cached entries
 	int m_max_size;
 

include/libtorrent/resolver_interface.hpp

@@ -48,14 +48,22 @@ struct resolver_interface
 	typedef boost::function<void(error_code const&, std::vector<address> const&)>
 		callback_t;
 
-	// prefer_cache will always use the cache if we have
-	// an entry, regardless of how old it is. This is usefull
-	// when completing the lookup quickly is more important
-	// than accuracy
-	enum flags_t { prefer_cache = 1 };
+	enum flags_t
+	{
+		// this flag will make async_resolve() always use the cache if we have an
+		// entry, regardless of how old it is. This is usefull when completing the
+		// lookup quickly is more important than accuracy
+		prefer_cache = 1,
+
+		// set this flag for lookups that are not critical during shutdown. i.e.
+		// for looking up tracker names _except_ when stopping a tracker.
+		abort_on_shutdown = 2
+	};
 
 	virtual void async_resolve(std::string const& host, int flags
 		, callback_t const& h) = 0;
+
+	virtual void abort() = 0;
 };
 
 }

src/http_tracker_connection.cpp

@@ -231,7 +231,7 @@ namespace libtorrent
 			, bind_interface()
 			, tracker_req().event == tracker_request::stopped
 				? resolver_interface::prefer_cache
-				: 0
+				: resolver_interface::abort_on_shutdown
 #if TORRENT_USE_I2P
 			, m_i2p_conn
 #endif

src/resolver.cpp

@@ -39,6 +39,7 @@ namespace libtorrent
 	resolver::resolver(io_service& ios)
 		: m_ios(ios)
 		, m_resolver(ios)
+		, m_critical_resolver(ios)
 		, m_max_size(700)
 		, m_timeout(seconds(1200))
 	{}
@@ -108,8 +109,21 @@ namespace libtorrent
 #if defined TORRENT_ASIO_DEBUGGING
 		add_outstanding_async("resolver::on_lookup");
 #endif
-		m_resolver.async_resolve(q, boost::bind(&resolver::on_lookup, this, _1, _2
-			, h, host));
+		if (flags & resolver_interface::abort_on_shutdown)
+		{
+			m_resolver.async_resolve(q, boost::bind(&resolver::on_lookup, this, _1, _2
+				, h, host));
+		}
+		else
+		{
+			m_critical_resolver.async_resolve(q, boost::bind(&resolver::on_lookup, this, _1, _2
+				, h, host));
+		}
+	}
+
+	void resolver::abort()
+	{
+		m_resolver.cancel();
 	}
 }
 

src/session_impl.cpp

@@ -979,6 +979,12 @@ namespace aux {
 #if defined TORRENT_LOGGING
 		session_log(" *** ABORT CALLED ***");
 #endif
+
+		// this will cancel requests that are not critical for shutting down
+		// cleanly. i.e. essentially tracker hostname lookups that we're not
+		// about to send event=stopped to
+		m_host_resolver.abort();
+
 		// abort the main thread
 		m_abort = true;
 		error_code ec;
@@ -5340,7 +5346,7 @@ retry:
 #if defined TORRENT_ASIO_DEBUGGING
 		add_outstanding_async("session_impl::on_dht_router_name_lookup");
 #endif
-		m_host_resolver.async_resolve(node.first, 0
+		m_host_resolver.async_resolve(node.first, resolver_interface::abort_on_shutdown
 			, boost::bind(&session_impl::on_dht_router_name_lookup
 				, this, _1, _2, node.second));
 	}

src/torrent.cpp

@@ -3236,7 +3236,7 @@ namespace libtorrent
 #if defined TORRENT_ASIO_DEBUGGING
 				add_outstanding_async("torrent::on_peer_name_lookup");
 #endif
-				m_ses.async_resolve(i->hostname, 0
+				m_ses.async_resolve(i->hostname, resolver_interface::abort_on_shutdown
 					, boost::bind(&torrent::on_peer_name_lookup
 						, shared_from_this(), _1, _2, i->port));
 			}
@@ -5990,7 +5990,7 @@ namespace libtorrent
 
 			// use proxy
 			web->resolving = true;
-			m_ses.async_resolve(ps.hostname, 0
+			m_ses.async_resolve(ps.hostname, resolver_interface::abort_on_shutdown
 				, boost::bind(&torrent::on_proxy_name_lookup, shared_from_this()
 					, _1, _2, web, ps.port));
 		}
@@ -6007,8 +6007,8 @@ namespace libtorrent
 #endif
 
 			web->resolving = true;
-			m_ses.async_resolve(hostname, 0, boost::bind(
-				&torrent::on_name_lookup, shared_from_this(), _1, _2
+			m_ses.async_resolve(hostname, resolver_interface::abort_on_shutdown
+				, boost::bind(&torrent::on_name_lookup, shared_from_this(), _1, _2
 				, port, web, tcp::endpoint()));
 		}
 	}
@@ -6091,8 +6091,8 @@ namespace libtorrent
 		}
 
 		web->resolving = true;
-		m_ses.async_resolve(hostname, 0, boost::bind(
-			&torrent::on_name_lookup, shared_from_this(), _1, _2
+		m_ses.async_resolve(hostname, resolver_interface::abort_on_shutdown
+			, boost::bind(&torrent::on_name_lookup, shared_from_this(), _1, _2
 			, port, web, a));
 	}
 
@@ -6368,7 +6368,7 @@ namespace libtorrent
 			return;
 		}
 		m_resolving_country = true;
-		m_ses.async_resolve(hostname, 0
+		m_ses.async_resolve(hostname, resolver_interface::abort_on_shutdown
 			, boost::bind(&torrent::on_country_lookup, shared_from_this(), _1, _2, p));
 	}
 

src/udp_socket.cpp

@@ -773,6 +773,8 @@ void udp_socket::set_proxy_settings(proxy_settings const& ps)
 	{
 		m_queue_packets = true;
 		// connect to socks5 server and open up the UDP tunnel
+
+		// TODO: use the system resolver_interface here
 		tcp::resolver::query q(ps.hostname, to_string(ps.port).elems);
 		++m_outstanding_ops;
 #if TORRENT_USE_ASSERTS

src/udp_tracker_connection.cpp

@@ -120,7 +120,7 @@ namespace libtorrent
 			m_man.host_resolver().async_resolve(hostname
 				, tracker_req().event == tracker_request::stopped
 					? resolver_interface::prefer_cache
-					: 0
+					: resolver_interface::abort_on_shutdown
 				, boost::bind(&udp_tracker_connection::name_lookup
 					, shared_from_this(), _1, _2, port));