bzr commit into mysql-6.0 branch (hezx:2693) Bug#39361

[He Zhenxing]

#At file:///media/sda3/work/mysql/bzrwork/b39361/6.0-rpl/

 2693 He Zhenxing	2008-09-10
      BUG#39361 backup_views failed: Lost connection to MySQL server during query
      
      thd->mysys_var was not reset to NULL before calling thd->store_globals() and 
      cause a assertion to fail, which is fixed by this patch.
modified:
  sql/si_objects.cc

=== modified file 'sql/si_objects.cc'
--- a/sql/si_objects.cc	2008-08-27 12:49:58 +0000
+++ b/sql/si_objects.cc	2008-09-10 08:07:04 +0000
@@ -1341,6 +1341,10 @@ ViewBaseObjectsIterator::create(THD *thd
 
   my_thd->thread_stack= (char*) &my_thd;
   my_thd->store_globals();
+  
+  /* after store_globals(), my_thd->mysys_var and thd->mysys_var
+     should point to the same instance */
+  DBUG_ASSERT(my_thd->mysys_var == thd->mysys_var);
   lex_start(my_thd);
 
   TABLE_LIST *tl =
@@ -1354,6 +1358,14 @@ ViewBaseObjectsIterator::create(THD *thd
   {
     close_thread_tables(my_thd);
     delete my_thd;
+
+    /* my_thd->mysys_var and thd->mysys_var points to the same
+       instance, after deletion of my_thd, my_thd->mysys_var is freed,
+       so thd->mysys_var is no long valid and must be set to NULL */
+    pthread_mutex_lock(&thd->LOCK_delete);
+    thd->mysys_var= NULL;
+    pthread_mutex_unlock(&thd->LOCK_delete);
+
     thd->store_globals();
 
     return NULL;