diff --git a/Gazebo_exercise/gazebo7_7.14.0_exercise/gazebo/physics/World.cc b/Gazebo_exercise/gazebo7_7.14.0_exercise/gazebo/physics/World.cc
index 9ea63f9..fd22232 100644
--- a/Gazebo_exercise/gazebo7_7.14.0_exercise/gazebo/physics/World.cc
+++ b/Gazebo_exercise/gazebo7_7.14.0_exercise/gazebo/physics/World.cc
@@ -175,6 +175,21 @@ World::~World()
 
   delete this->dataPtr;
   this->dataPtr = nullptr;
+  ////////////////Added by zenglei for Asyn event and processMessages///////////////
+  if (this->dataPtr->event_thread)            
+  {
+    this->dataPtr->event_thread->join();
+    delete this->dataPtr->event_thread;
+    this->dataPtr->event_thread = nullptr;
+  }
+
+  if(this->dataPtr->async_processmessages_thread)
+  {
+    this->dataPtr->async_processmessages_thread->join();
+    delete this->dataPtr->async_processmessages_thread;
+    this->dataPtr->async_processmessages_thread = nullptr;
+  }
+  //////////////////////////////////////////////////////////////////////////////////
 }
 
 //////////////////////////////////////////////////
@@ -1352,6 +1367,24 @@ void World::Fini()
     delete this->dataPtr->thread;
     this->dataPtr->thread = nullptr;
   }
+
+  /////////////////Added for asyn event by zenglei/////////////////////
+
+  if (this->dataPtr->event_thread)            
+  {
+    this->dataPtr->event_thread->join();
+    delete this->dataPtr->event_thread;
+    this->dataPtr->event_thread = nullptr;
+  }
+
+  if(this->dataPtr->async_processmessages_thread)
+  {
+    this->dataPtr->async_processmessages_thread->join();
+    delete this->dataPtr->async_processmessages_thread;
+    this->dataPtr->async_processmessages_thread = nullptr;
+  }
+
+  //////////////////////////////////////////////////////////////////////
 }
 
 //////////////////////////////////////////////////