fixed udp tracker race condition

ChangeLog

@@ -107,6 +107,7 @@
 	* improved LSD performance and made the interval configurable
 	* improved UDP tracker support by caching connect tokens
 	* fast piece optimization
+	* fixed udp tracker race condition
 	* added support for torrents with odd piece sizes
 	* fixed issue with disk read cache not being cleared when removing torrents
 	* made the DHT socket bind to the same interface as the session

include/libtorrent/tracker_manager.hpp

@@ -160,6 +160,7 @@ namespace libtorrent
 		void set_timeout(int completion_timeout, int read_timeout);
 		void restart_read_timeout();
 		void cancel();
+		bool cancelled() const { return m_abort; }
 
 		virtual void on_timeout() = 0;
 		virtual ~timeout_handler() {}

src/udp_tracker_connection.cpp

@@ -131,6 +131,12 @@ namespace libtorrent
 #if defined TORRENT_VERBOSE_LOGGING || defined TORRENT_LOGGING
 		if (cb) cb->debug_log("*** UDP_TRACKER [ name lookup successful ]");
 #endif
+		if (cancelled())
+		{
+			fail(-1, "aborted");
+			return;
+		}
+
 		restart_read_timeout();
 		
 		// look for an address that has the same kind as the one