Backport of:

------------------------------------------------------------
revno: 2630.4.32
committer: Dmitry Lenev <dlenev@mysql.com>
branch nick: mysql-6.0-3726-w2
timestamp: Thu 2008-06-19 16:39:58 +0400
message:
  WL#3726 "DDL locking for all metadata objects".

  After-review fixes in progress.

  Ensure that metadata locking subsystem properly handles
  out-of-memory conditions. Clarified MDL interface by
  separating release of locks and removal of lock requests
  from the context.

sql/lock.cc:
  mdl_release_lock(), mdl_acquire_exclusive_locks() and 
  mdl_try_acquire_exclusive_lock() are no longer responsible
  for removal of metadata lock requests from the context.
  One should explicitly call mdl_remove_all_locks() and
  mdl_remove_lock() to do this.
sql/mdl.cc:
  Ensured that metadata locking subsystem properly handles
  out-of-memory conditions.
  Introduced new MDL_INITIALIZED state for metadata lock
  request which is used in all cases when lock is not acquired 
  and we have not associated request with object respesenting 
  lock.
  
  MDL_PENDING is now only used for requests for exclusive locks
  which are added to the MDL_LOCK::waiting_exclusive queue.
  mdl_release_lock(), mdl_acquire_exclusive_locks() and 
  mdl_try_acquire_exclusive_lock() are no longer responsible
  for removal of metadata lock requests from the context.
  One should explicitly call mdl_remove_all_locks() and
  newly introduced mdl_remove_lock() to do this.
  Also renamed mdl_release_all_locks_for_name() to 
  emphasize that it also actually removes lock requests
  from the context.
  
  Finally mdl_try_acquire_exclusive_lock() is now returs
  information about encountered lock conflict in separate
  out parameter since its return value is used for distinguishing
  between error (e.g. due to OOM) and success.
sql/mdl.h:
  Introduced new MDL_INITIALIZED state for metadata lock
  request which is used in all cases when lock is not acquired 
  and we have not associated request with object respesenting 
  lock.
  
  MDL_PENDING is now only used for requests for exclusive locks
  which are added to the MDL_LOCK::waiting_exclusive queue.
  mdl_release_lock(), mdl_acquire_exclusive_locks() and 
  mdl_try_acquire_exclusive_lock() are no longer responsible
  for removal of metadata lock requests from the context.
  One should explicitly call mdl_remove_all_locks() and
  newly introduced mdl_remove_lock() to do this.
  Also renamed mdl_release_all_locks_for_name() to 
  emphasize that it also actually removes lock requests
  from the context.
  
  Finally mdl_try_acquire_exclusive_lock() is now returs
  information about encountered lock conflict in separate
  out parameter since its return value is used for distinguishing
  between error (e.g. due to OOM) and success.
sql/sql_base.cc:
  mdl_release_lock(), mdl_acquire_exclusive_locks() and mdl_try_acquire_exclusive_lock() are no longer responsible
  for removal of metadata lock requests from the context.
  One should explicitly call mdl_remove_all_locks() and
  mdl_remove_lock() to do this.
  Also adjusted open_table() to ensure that it 
  releases/removes metadata locks in case of error 
  after adding/acquiring them (unless keeping these
  lock requests is required for recovering action).
sql/sql_delete.cc:
  mdl_release_lock(), mdl_acquire_exclusive_locks() and mdl_try_acquire_exclusive_lock() are no longer responsible
  for removal of metadata lock requests from the context.
  One should explicitly call mdl_remove_all_locks() and
  mdl_remove_lock() to do this.
sql/sql_handler.cc:
  mdl_release_lock(), mdl_acquire_exclusive_locks() and mdl_try_acquire_exclusive_lock() are no longer responsible
  for removal of metadata lock requests from the context.
  One should explicitly call mdl_remove_all_locks() and
  mdl_remove_lock() to do this.
sql/sql_show.cc:
  mdl_release_lock(), mdl_acquire_exclusive_locks() and mdl_try_acquire_exclusive_lock() are no longer responsible
  for removal of metadata lock requests from the context.
  One should explicitly call mdl_remove_all_locks() and
  mdl_remove_lock() to do this.
sql/sql_table.cc:
  Renamed mdl_release_all_locks_for_name() to emphasize
  that it also actually removes lock requests from the context.
  mdl_release_lock(), mdl_acquire_exclusive_locks() and mdl_try_acquire_exclusive_lock() are no longer responsible
  for removal of metadata lock requests from the context.
  One should explicitly call mdl_remove_all_locks() and
  mdl_remove_lock() to do this.
  Finally mdl_try_acquire_exclusive_lock() is now returs
  information about encountered lock conflict in separate
  out parameter since its return value is used for distinguishing
  between error (e.g. due to OOM) and success.

sql/lock.cc

@@ -965,7 +965,7 @@ bool lock_table_names(THD *thd, TABLE_LIST *table_list)
     lock_table->mdl_lock_data= mdl_lock_data;
   }
   if (mdl_acquire_exclusive_locks(&thd->mdl_context))
-    return 1;
+    goto end;
   return 0;
 
 end:

sql/mdl.h

@@ -44,7 +44,8 @@ enum enum_mdl_type {MDL_SHARED=0, MDL_SHARED_HIGH_PRIO,
 
 /** States which metadata lock request can have. */
 
-enum enum_mdl_state {MDL_PENDING=0, MDL_ACQUIRED, MDL_PENDING_UPGRADE};
+enum enum_mdl_state {MDL_INITIALIZED=0, MDL_PENDING,
+                     MDL_ACQUIRED, MDL_PENDING_UPGRADE};
 
 
 /**
@@ -152,6 +153,7 @@ void mdl_init_lock(MDL_LOCK_DATA *lock_data, char *key, int type,
 MDL_LOCK_DATA *mdl_alloc_lock(int type, const char *db, const char *name,
                               MEM_ROOT *root);
 void mdl_add_lock(MDL_CONTEXT *context, MDL_LOCK_DATA *lock_data);
+void mdl_remove_lock(MDL_CONTEXT *context, MDL_LOCK_DATA *lock_data);
 void mdl_remove_all_locks(MDL_CONTEXT *context);
 
 /**
@@ -160,7 +162,7 @@ void mdl_remove_all_locks(MDL_CONTEXT *context);
 
 inline void mdl_set_lock_type(MDL_LOCK_DATA *lock_data, enum_mdl_type lock_type)
 {
-  DBUG_ASSERT(lock_data->state == MDL_PENDING);
+  DBUG_ASSERT(lock_data->state == MDL_INITIALIZED);
   lock_data->type= lock_type;
 }
 
@@ -170,14 +172,15 @@ bool mdl_acquire_exclusive_locks(MDL_CONTEXT *context);
 bool mdl_upgrade_shared_lock_to_exclusive(MDL_CONTEXT *context,
                                           MDL_LOCK_DATA *lock_data);
 bool mdl_try_acquire_exclusive_lock(MDL_CONTEXT *context,
-                                    MDL_LOCK_DATA *lock_data);
+                                    MDL_LOCK_DATA *lock_data,
+                                    bool *conflict);
 bool mdl_acquire_global_shared_lock(MDL_CONTEXT *context);
 
 bool mdl_wait_for_locks(MDL_CONTEXT *context);
 
 void mdl_release_locks(MDL_CONTEXT *context);
-void mdl_release_all_locks_for_name(MDL_CONTEXT *context,
-                                    MDL_LOCK_DATA *lock_data);
+void mdl_release_and_remove_all_locks_for_name(MDL_CONTEXT *context,
+                                               MDL_LOCK_DATA *lock_data);
 void mdl_release_lock(MDL_CONTEXT *context, MDL_LOCK_DATA *lock_data);
 void mdl_downgrade_exclusive_lock(MDL_CONTEXT *context,
                                   MDL_LOCK_DATA *lock_data);

sql/sql_base.cc

@@ -2278,9 +2278,9 @@ void table_share_release_hook(void *share)
 }
 
 
-/*
-  A helper function that acquires an MDL lock for a table
-  being opened.
+/**
+   A helper function that acquires an MDL lock for a table
+   being opened.
 */
 
 static bool
@@ -2304,7 +2304,10 @@ open_table_get_mdl_lock(THD *thd, TABLE_LIST *table_list,
     */
     mdl_set_lock_type(mdl_lock_data, MDL_EXCLUSIVE);
     if (mdl_acquire_exclusive_locks(&thd->mdl_context))
+    {
+      mdl_remove_lock(&thd->mdl_context, mdl_lock_data);
       return 1;
+    }
   }
   else
   {
@@ -2327,6 +2330,8 @@ open_table_get_mdl_lock(THD *thd, TABLE_LIST *table_list,
     {
       if (retry)
         *action= OT_BACK_OFF_AND_RETRY;
+      else
+        mdl_remove_lock(&thd->mdl_context, mdl_lock_data);
       return 1;
     }
   }
@@ -2833,7 +2838,11 @@ bool open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
   release_table_share(share);
 err_unlock2:
   pthread_mutex_unlock(&LOCK_open);
-  mdl_release_lock(&thd->mdl_context, mdl_lock_data);
+  if (! (flags & MYSQL_OPEN_HAS_MDL_LOCK))
+  {
+    mdl_release_lock(&thd->mdl_context, mdl_lock_data);
+    mdl_remove_lock(&thd->mdl_context, mdl_lock_data);
+  }
   DBUG_RETURN(TRUE);
 }
 
@@ -3497,7 +3506,10 @@ recover_from_failed_open_table_attempt(THD *thd, TABLE_LIST *table,
       mdl_set_lock_type(table->mdl_lock_data, MDL_EXCLUSIVE);
       mdl_add_lock(&thd->mdl_context, table->mdl_lock_data);
       if (mdl_acquire_exclusive_locks(&thd->mdl_context))
+      {
+        mdl_remove_lock(&thd->mdl_context, table->mdl_lock_data);
         return TRUE;
+      }
       pthread_mutex_lock(&LOCK_open);
       tdc_remove_table(thd, TDC_RT_REMOVE_ALL, table->db, table->table_name);
       ha_create_table_from_engine(thd, table->db, table->table_name);
@@ -3506,18 +3518,23 @@ recover_from_failed_open_table_attempt(THD *thd, TABLE_LIST *table,
       thd->warning_info->clear_warning_info(thd->query_id);
       thd->clear_error();                 // Clear error message
       mdl_release_lock(&thd->mdl_context, table->mdl_lock_data);
+      mdl_remove_lock(&thd->mdl_context, table->mdl_lock_data);
       break;
     case OT_REPAIR:
       mdl_set_lock_type(table->mdl_lock_data, MDL_EXCLUSIVE);
       mdl_add_lock(&thd->mdl_context, table->mdl_lock_data);
       if (mdl_acquire_exclusive_locks(&thd->mdl_context))
+      {
+        mdl_remove_lock(&thd->mdl_context, table->mdl_lock_data);
         return TRUE;
+      }
       pthread_mutex_lock(&LOCK_open);
       tdc_remove_table(thd, TDC_RT_REMOVE_ALL, table->db, table->table_name);
       pthread_mutex_unlock(&LOCK_open);
 
       result= auto_repair_table(thd, table);
       mdl_release_lock(&thd->mdl_context, table->mdl_lock_data);
+      mdl_remove_lock(&thd->mdl_context, table->mdl_lock_data);
       break;
     default:
       DBUG_ASSERT(0);

sql/sql_delete.cc

@@ -1170,7 +1170,10 @@ bool mysql_truncate(THD *thd, TABLE_LIST *table_list, bool dont_send_ok)
     mdl_set_lock_type(mdl_lock_data, MDL_EXCLUSIVE);
     mdl_add_lock(&thd->mdl_context, mdl_lock_data);
     if (mdl_acquire_exclusive_locks(&thd->mdl_context))
+    {
+      mdl_remove_lock(&thd->mdl_context, mdl_lock_data);
       DBUG_RETURN(TRUE);
+    }
     pthread_mutex_lock(&LOCK_open);
     tdc_remove_table(thd, TDC_RT_REMOVE_ALL, table_list->db,
                      table_list->table_name);
@@ -1200,12 +1203,18 @@ bool mysql_truncate(THD *thd, TABLE_LIST *table_list, bool dont_send_ok)
       my_ok(thd);		// This should return record count
     }
     if (mdl_lock_data)
+    {
       mdl_release_lock(&thd->mdl_context, mdl_lock_data);
+      mdl_remove_lock(&thd->mdl_context, mdl_lock_data);
+    }
   }
   else if (error)
   {
     if (mdl_lock_data)
+    {
       mdl_release_lock(&thd->mdl_context, mdl_lock_data);
+      mdl_remove_lock(&thd->mdl_context, mdl_lock_data);
+    }
   }
   DBUG_RETURN(error);
 

sql/sql_handler.cc

@@ -150,6 +150,7 @@ static void mysql_ha_close_table(THD *thd, TABLE_LIST *tables)
     }
     pthread_mutex_unlock(&LOCK_open);
     mdl_release_lock(&thd->handler_mdl_context, mdl_lock_data);
+    mdl_remove_lock(&thd->handler_mdl_context, mdl_lock_data);
   }
   else if (tables->table)
   {

sql/sql_show.cc

@@ -3250,6 +3250,7 @@ static int fill_schema_table_from_frm(THD *thd,TABLE *table,
 
 err:
   mdl_release_lock(&thd->mdl_context, &mdl_lock_data);
+  mdl_remove_lock(&thd->mdl_context, &mdl_lock_data);
   thd->clear_error();
   return res;
 }

sql/sql_table.cc

@@ -2208,7 +2208,8 @@ int mysql_rm_table_part2(THD *thd, TABLE_LIST *tables, bool if_exists,
           and locked and therefore have to remove several metadata lock
           requests associated with them.
         */
-        mdl_release_all_locks_for_name(&thd->mdl_context, table->mdl_lock_data);
+        mdl_release_and_remove_all_locks_for_name(&thd->mdl_context,
+                                                  table->mdl_lock_data);
       }
     }
   }
@@ -4080,13 +4081,27 @@ static bool lock_table_name_if_not_cached(THD *thd, const char *db,
                                           const char *table_name,
                                           MDL_LOCK_DATA **lock_data)
 {
+  bool conflict;
+
   if (!(*lock_data= mdl_alloc_lock(0, db, table_name, thd->mem_root)))
     return TRUE;
   mdl_set_lock_type(*lock_data, MDL_EXCLUSIVE);
   mdl_add_lock(&thd->mdl_context, *lock_data);
-  if (mdl_try_acquire_exclusive_lock(&thd->mdl_context, *lock_data))
+  if (mdl_try_acquire_exclusive_lock(&thd->mdl_context, *lock_data,
+                                     &conflict))
   {
-    *lock_data= 0;
+    /*
+      To simplify our life under LOCK TABLES we remove unsatisfied
+      lock request from the context.
+    */
+    mdl_remove_lock(&thd->mdl_context, *lock_data);
+    if (!conflict)
+    {
+      /* Probably OOM. */
+      return TRUE;
+    }
+    else
+      *lock_data= 0;
   }
   return FALSE;
 }
@@ -4157,7 +4172,10 @@ bool mysql_create_table(THD *thd, const char *db, const char *table_name,
 
 unlock:
   if (target_lock_data)
+  {
     mdl_release_lock(&thd->mdl_context, target_lock_data);
+    mdl_remove_lock(&thd->mdl_context, target_lock_data);
+  }
   pthread_mutex_lock(&LOCK_lock_db);
   if (!--creating_table && creating_database)
     pthread_cond_signal(&COND_refresh);
@@ -4416,7 +4434,10 @@ static int prepare_for_repair(THD *thd, TABLE_LIST *table_list,
     mdl_set_lock_type(mdl_lock_data, MDL_EXCLUSIVE);
     mdl_add_lock(&thd->mdl_context, mdl_lock_data);
     if (mdl_acquire_exclusive_locks(&thd->mdl_context))
+    {
+      mdl_remove_lock(&thd->mdl_context, mdl_lock_data);
       DBUG_RETURN(0);
+    }
 
     pthread_mutex_lock(&LOCK_open);
     if (!(share= (get_table_share(thd, table_list, key, key_length, 0,
@@ -4550,7 +4571,10 @@ static int prepare_for_repair(THD *thd, TABLE_LIST *table_list,
   }
   /* In case of a temporary table there will be no metadata lock. */
   if (error && mdl_lock_data)
+  {
     mdl_release_lock(&thd->mdl_context, mdl_lock_data);
+    mdl_remove_lock(&thd->mdl_context, mdl_lock_data);
+  }
   DBUG_RETURN(error);
 }
 
@@ -5518,7 +5542,10 @@ goto binlog;
 
 err:
   if (target_lock_data)
+  {
     mdl_release_lock(&thd->mdl_context, target_lock_data);
+    mdl_remove_lock(&thd->mdl_context, target_lock_data);
+  }
   DBUG_RETURN(res);
 }
 
@@ -6876,7 +6903,9 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
       if (new_name != table_name || new_db != db)
       {
         mdl_release_lock(&thd->mdl_context, target_lock_data);
-        mdl_release_all_locks_for_name(&thd->mdl_context, mdl_lock_data);
+        mdl_remove_lock(&thd->mdl_context, target_lock_data);
+        mdl_release_and_remove_all_locks_for_name(&thd->mdl_context,
+                                                  mdl_lock_data);
       }
       else
         mdl_downgrade_exclusive_lock(&thd->mdl_context, mdl_lock_data);
@@ -7554,7 +7583,9 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
     if ((new_name != table_name || new_db != db))
     {
       mdl_release_lock(&thd->mdl_context, target_lock_data);
-      mdl_release_all_locks_for_name(&thd->mdl_context, mdl_lock_data);
+      mdl_remove_lock(&thd->mdl_context, target_lock_data);
+      mdl_release_and_remove_all_locks_for_name(&thd->mdl_context,
+                                                mdl_lock_data);
     }
     else
       mdl_downgrade_exclusive_lock(&thd->mdl_context, mdl_lock_data);
@@ -7613,7 +7644,10 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
     thd->abort_on_warning= save_abort_on_warning;
   }
   if (target_lock_data)
+  {
     mdl_release_lock(&thd->mdl_context, target_lock_data);
+    mdl_remove_lock(&thd->mdl_context, target_lock_data);
+  }
   DBUG_RETURN(TRUE);
 
 err_with_mdl:
@@ -7625,8 +7659,11 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
   */
   thd->locked_tables_list.unlink_all_closed_tables();
   if (target_lock_data)
+  {
     mdl_release_lock(&thd->mdl_context, target_lock_data);
-  mdl_release_all_locks_for_name(&thd->mdl_context, mdl_lock_data);
+    mdl_remove_lock(&thd->mdl_context, target_lock_data);
+  }
+  mdl_release_and_remove_all_locks_for_name(&thd->mdl_context, mdl_lock_data);
   DBUG_RETURN(TRUE);
 }
 /* mysql_alter_table */