Bug#19437 (Connection refused by server: "2002 Can't connect... /master.sock"):

Clearing active VIO before calling mysql_close() in the slave I/O
thread. 


sql/slave.cc:
  Clearing active VIO before calling mysql_close() in the slave I/O thread.

sql/slave.cc

@@ -1653,6 +1653,15 @@ int fetch_master_table(THD *thd, const char *db_name, const char *table_name,
     if (connect_to_master(thd, mysql, mi))
     {
       my_error(ER_CONNECT_TO_MASTER, MYF(0), mysql_error(mysql));
+      /*
+        We need to clear the active VIO since, theoretically, somebody
+        might issue an awake() on this thread.  If we are then in the
+        middle of closing and destroying the VIO inside the
+        mysql_close(), we will have a problem.
+       */
+#ifdef SIGNAL_WITH_VIO_CLOSE
+      thd->clear_active_vio();
+#endif
       mysql_close(mysql);
       DBUG_RETURN(1);
     }
@@ -3709,6 +3718,17 @@ err:
   VOID(pthread_mutex_unlock(&LOCK_thread_count));
   if (mysql)
   {
+    /*
+      Here we need to clear the active VIO before closing the
+      connection with the master.  The reason is that THD::awake()
+      might be called from terminate_slave_thread() because somebody
+      issued a STOP SLAVE.  If that happends, the close_active_vio()
+      can be called in the middle of closing the VIO associated with
+      the 'mysql' object, causing a crash.
+    */
+#ifdef SIGNAL_WITH_VIO_CLOSE
+    thd->clear_active_vio();
+#endif
     mysql_close(mysql);
     mi->mysql=0;
   }