- implement inheritance of sp_instr: public Query_arena.

  We need every instruction to have its own arena, because we want to
  track instruction's state (INITIALIZED_FOR_SP -> EXECUTED). Because of 
  `if' statements and other conditional instructions used in stored 
  procedures, not every instruction of a stored procedure gets executed 
  during the first (or even subsequent) execution of the procedure. 
  So it's better if we track the execution state of every instruction 
  independently.
  All instructions of a given procedure now also share sp_head's 
  mem_root, but keep their own free_list.
  This simplifies juggling with free Item lists in sp_head::execute.
- free_items() moved to be a member of Query_arena. 
- logic of 'backup_arena' debug member of Query_arena has been
  changed to support
  multi-backups. Until now, TRUE 'backup_arena' meant that there is
  exactly one active backup of the THD arena. Now it means simply that
  the arena is used for backup, so that we can't accidentally overwrite an 
  existing backup. This allows doing multiple backups, e.g. in
  sp_head::execute and Cursor::fetch, when THD arena is already backed up
  but we want to set yet another arena (usually the 'permanent' arena,
  to save permanent transformations/optimizations of a parsed tree).


sql/sp_head.cc:
  - use Query_arena support in sp_head::execute() as now sp_instr inherites
    from it.
sql/sp_head.h:
  - inherite sp_instr from Query_arena
sql/sql_class.cc:
  - changed the principle of Query_arena::backup_arena; free_items is now
    a member of Query_arena.
sql/sql_class.h:
  - changed the principle of Query_arena::backup_arena; free_items is now
    a member of Query_arena.
sql/sql_prepare.cc:
  free_items() is now a member of Query_arena.
sql/sql_select.cc:
  free_items() now automatically sets free_list to zero.

1 files changed, 20 insertions, 7 deletions

diff --git a/sql/sql_class.cc b/sql/sql_class.cc
index 8abd7cbbe7d..20f48da9283 100644
--- a/sql/sql_class.cc
+++ b/sql/sql_class.cc
@@ -171,9 +171,6 @@ THD::THD()
    spcont(NULL)
 {
   current_arena= this;
-#ifndef DBUG_OFF
-  backup_arena= 0;
-#endif
   host= user= priv_user= db= ip= 0;
   catalog= (char*)"std"; // the only catalog we have for now
   host_or_ip= "connecting host";
@@ -528,7 +525,7 @@ void THD::cleanup_after_query()
     next_insert_id= 0;
   }
   /* Free Items that were created during this execution */
-  free_items(free_list);
+  free_items();
   /*
     In the rest of code we assume that free_list never points to garbage:
     Keep this predicate true.
@@ -1485,6 +1482,21 @@ Query_arena::Type Query_arena::type() const
 }
 
 
+void Query_arena::free_items()
+{
+  Item *next;
+  DBUG_ENTER("Query_arena::free_items");
+  /* This works because items are allocated with sql_alloc() */
+  for (; free_list; free_list= next)
+  {
+    next= free_list->next;
+    free_list->delete_self();
+  }
+  /* Postcondition: free_list is 0 */
+  DBUG_VOID_RETURN;
+}
+
+
 /*
   Statement functions 
 */
@@ -1556,11 +1568,11 @@ void THD::end_statement()
 void Query_arena::set_n_backup_item_arena(Query_arena *set, Query_arena *backup)
 {
   DBUG_ENTER("Query_arena::set_n_backup_item_arena");
-  DBUG_ASSERT(backup_arena == 0);
+  DBUG_ASSERT(backup->is_backup_arena == FALSE);
   backup->set_item_arena(this);
   set_item_arena(set);
 #ifndef DBUG_OFF
-  backup_arena= 1;
+  backup->is_backup_arena= TRUE;
 #endif
   DBUG_VOID_RETURN;
 }
@@ -1569,10 +1581,11 @@ void Query_arena::set_n_backup_item_arena(Query_arena *set, Query_arena *backup)
 void Query_arena::restore_backup_item_arena(Query_arena *set, Query_arena *backup)
 {
   DBUG_ENTER("Query_arena::restore_backup_item_arena");
+  DBUG_ASSERT(backup->is_backup_arena);
   set->set_item_arena(this);
   set_item_arena(backup);
 #ifndef DBUG_OFF
-  backup_arena= 0;
+  backup->is_backup_arena= FALSE;
 #endif
   DBUG_VOID_RETURN;
 }