From 122ffa22112ebc78a63e39cc2fcc7b9da3675926 Mon Sep 17 00:00:00 2001
From: Aleksey Midenkov <midenok@gmail.com>
Date: Thu, 27 Apr 2017 10:24:16 +0300
Subject: [PATCH] SQL(misc): Query_arena_stmt RAII

---
 sql/sql_class.cc   | 13 +++++++++++++
 sql/sql_class.h    | 16 ++++++++++++++++
 sql/sql_derived.cc |  5 +----
 sql/sql_select.cc  | 10 ++--------
 4 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/sql/sql_class.cc b/sql/sql_class.cc
index 1a422fd9966..052e5ae136d 100644
--- a/sql/sql_class.cc
+++ b/sql/sql_class.cc
@@ -7425,3 +7425,16 @@ bool Discrete_intervals_list::append(Discrete_interval *new_interval)
 }
 
 #endif /* !defined(MYSQL_CLIENT) */
+
+
+Query_arena_stmt::Query_arena_stmt(THD *_thd) :
+  thd(_thd)
+{
+  arena= thd->activate_stmt_arena_if_needed(&backup);
+}
+
+Query_arena_stmt::~Query_arena_stmt()
+{
+  if (arena)
+    thd->restore_active_arena(arena, &backup);
+}
diff --git a/sql/sql_class.h b/sql/sql_class.h
index 303992c40d8..b76b5cd6e60 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -1024,6 +1024,22 @@ public:
 };
 
 
+class Query_arena_stmt
+{
+  THD *thd;
+  Query_arena backup;
+  Query_arena *arena;
+
+public:
+  Query_arena_stmt(THD *_thd);
+  ~Query_arena_stmt();
+  bool arena_replaced()
+  {
+    return arena != NULL;
+  }
+};
+
+
 class Server_side_cursor;
 
 /**
diff --git a/sql/sql_derived.cc b/sql/sql_derived.cc
index 43302498d57..eb99544ea0b 100644
--- a/sql/sql_derived.cc
+++ b/sql/sql_derived.cc
@@ -723,14 +723,11 @@ bool mysql_derived_prepare(THD *thd, LEX *lex, TABLE_LIST *derived)
         TABLE_SHARE *s= tl->table->s;
         const char *db= tl->db;
         const char *alias= tl->alias;
-        Query_arena backup;
-        Query_arena *arena= thd->activate_stmt_arena_if_needed(&backup);
+        Query_arena_stmt on_stmt_arena(thd);
         sl->item_list.push_back(new (thd->mem_root) Item_field(
             thd, &sl->context, db, alias, s->vers_start_field()->field_name));
         sl->item_list.push_back(new (thd->mem_root) Item_field(
             thd, &sl->context, db, alias, s->vers_end_field()->field_name));
-        if (arena)
-          thd->restore_active_arena(arena, &backup);
       }
     }
   }
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 5901d1d4d6f..5ebd3126a23 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -695,7 +695,6 @@ int vers_setup_select(THD *thd, TABLE_LIST *tables, COND **where_expr,
   TABLE_LIST *table;
   int versioned_tables= 0;
   int slex_conds_used= 0;
-  Query_arena *arena= 0, backup;
 
   if (!thd->stmt_arena->is_conventional() &&
       !thd->stmt_arena->is_stmt_prepare() && !thd->stmt_arena->is_sp_execute())
@@ -727,7 +726,7 @@ int vers_setup_select(THD *thd, TABLE_LIST *tables, COND **where_expr,
 
   /* For prepared statements we create items on statement arena,
      because they must outlive execution phase for multiple executions. */
-  arena= thd->activate_stmt_arena_if_needed(&backup);
+  Query_arena_stmt on_stmt_arena(thd);
 
   if (slex->saved_where)
   {
@@ -798,8 +797,6 @@ int vers_setup_select(THD *thd, TABLE_LIST *tables, COND **where_expr,
         case TL_WRITE:
         case TL_WRITE_ONLY:
           my_error(ER_VERS_WRONG_PARAMS, MYF(0), "FOR SYSTEM_TIME query", "write-locking of historic rows");
-          if (arena)
-            thd->restore_active_arena(arena, &backup);
           DBUG_RETURN(-1);
         default:
           break;
@@ -969,7 +966,7 @@ int vers_setup_select(THD *thd, TABLE_LIST *tables, COND **where_expr,
             cond2,
             cond1));
 
-        if (arena)
+        if (on_stmt_arena.arena_replaced())
           *dst_cond= cond1;
         else
           thd->change_item_tree(dst_cond, cond1);
@@ -977,9 +974,6 @@ int vers_setup_select(THD *thd, TABLE_LIST *tables, COND **where_expr,
     } // if (... table->table->versioned())
   } // for (table= tables; ...)
 
-  if (arena)
-    thd->restore_active_arena(arena, &backup);
-
   if (!slex_conds_used && slex->vers_conditions)
   {
     my_error(ER_VERS_WRONG_QUERY, MYF(0), "unused `QUERY FOR SYSTEM_TIME` clause!");