fixed race condition when saving DHT state

ChangeLog

@@ -47,6 +47,7 @@ release 0.14.2
 	* fixed bug in http_connection when binding to a particular IP
 	* fixed typo in python binding (torrent_handle::piece_prioritize should
 	  be torrent_handle::piece_priorities)
+	* fixed race condition when saving DHT state
 
 release 0.14.1
 

include/libtorrent/aux_/session_impl.hpp

@@ -53,6 +53,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <boost/filesystem/path.hpp>
 #include <boost/thread.hpp>
 #include <boost/thread/recursive_mutex.hpp>
+#include <boost/thread/condition_variable.hpp>
 
 #ifdef _MSC_VER
 #pragma warning(pop)
@@ -176,6 +177,7 @@ namespace libtorrent
 			dht_settings const& get_dht_settings() const { return m_dht_settings; }
 			void start_dht(entry const& startup_state);
 			void stop_dht();
+
 			entry dht_state() const;
 			void maybe_update_udp_mapping(int nat, int local_port, int external_port);
 #endif
@@ -327,6 +329,8 @@ namespace libtorrent
 
 //		private:
 
+			void session_impl::dht_state_callback(boost::condition_variable_any& c
+				, entry& e, bool& done) const;
 			void on_lsd_peer(tcp::endpoint peer, sha1_hash const& ih);
 
 #ifndef TORRENT_DISABLE_POOL_ALLOCATOR
@@ -347,7 +351,7 @@ namespace libtorrent
 			// this is where all active sockets are stored.
 			// the selector can sleep while there's no activity on
 			// them
-			io_service m_io_service;
+			mutable io_service m_io_service;
 
 			// handles disk io requests asynchronously
 			// peers have pointers into the disk buffer

src/session_impl.cpp

@@ -2331,11 +2331,27 @@ namespace aux {
 			m_dht_settings.service_port = m_listen_interface.port();
 	}
 
+	void session_impl::dht_state_callback(boost::condition_variable_any& c
+		, entry& e, bool& done) const
+	{
+		if (m_dht) e = m_dht->state();
+		mutex_t::scoped_lock l(m_mutex);
+		done = true;
+		l.unlock();
+		c.notify_all();
+	}
+
 	entry session_impl::dht_state() const
 	{
+		boost::condition_variable_any cond;
 		mutex_t::scoped_lock l(m_mutex);
 		if (!m_dht) return entry();
-		return m_dht->state();
+		entry e;
+		bool done = false;
+		m_io_service.post(boost::bind(&session_impl::dht_state_callback
+			, this, boost::ref(cond), boost::ref(e), boost::ref(done)));
+		while (!done) cond.wait(l);
+		return e;
 	}
 
 	void session_impl::add_dht_node(std::pair<std::string, int> const& node)