A pre-requisite patch for the fix for Bug#52044.

This patch also fixes Bug#55452 "SET PASSWORD is
replicated twice in RBR mode".

The goal of this patch is to remove the release of 
metadata locks from close_thread_tables().
This is necessary to not mistakenly release
the locks in the course of a multi-step
operation that involves multiple close_thread_tables()
or close_tables_for_reopen().

On the same token, move statement commit outside 
close_thread_tables().

Other cleanups:
Cleanup COM_FIELD_LIST.
Don't call close_thread_tables() in COM_SHUTDOWN -- there
are no open tables there that can be closed (we leave
the locked tables mode in THD destructor, and this
close_thread_tables() won't leave it anyway).

Make open_and_lock_tables() and open_and_lock_tables_derived()
call close_thread_tables() upon failure.
Remove the calls to close_thread_tables() that are now
unnecessary.

Simplify the back off condition in Open_table_context.

Streamline metadata lock handling in LOCK TABLES 
implementation.

Add asserts to ensure correct life cycle of 
statement transaction in a session.

Remove a piece of dead code that has also become redundant
after the fix for Bug 37521.

1 files changed, 31 insertions, 43 deletions

diff --git a/sql/event_db_repository.cc b/sql/event_db_repository.cc
index b7c01f10066..d47f1641bb0 100644
--- a/sql/event_db_repository.cc
+++ b/sql/event_db_repository.cc
@@ -518,17 +518,20 @@ Event_db_repository::table_scan_all_for_i_s(THD *thd, TABLE *schema_table,
 */
 
 bool
-Event_db_repository::fill_schema_events(THD *thd, TABLE_LIST *tables,
+Event_db_repository::fill_schema_events(THD *thd, TABLE_LIST *i_s_table,
                                         const char *db)
 {
-  TABLE *schema_table= tables->table;
-  TABLE *event_table= NULL;
+  TABLE *schema_table= i_s_table->table;
+  Open_tables_backup open_tables_backup;
+  TABLE_LIST event_table;
   int ret= 0;
 
   DBUG_ENTER("Event_db_repository::fill_schema_events");
   DBUG_PRINT("info",("db=%s", db? db:"(null)"));
 
-  if (open_event_table(thd, TL_READ, &event_table))
+  event_table.init_one_table("mysql", 5, "event", 5, "event", TL_READ);
+
+  if (open_system_tables_for_read(thd, &event_table, &open_tables_backup))
     DBUG_RETURN(TRUE);
 
   /*
@@ -541,11 +544,11 @@ Event_db_repository::fill_schema_events(THD *thd, TABLE_LIST *tables,
                   every single row's `db` with the schema which we show.
   */
   if (db)
-    ret= index_read_for_db_for_i_s(thd, schema_table, event_table, db);
+    ret= index_read_for_db_for_i_s(thd, schema_table, event_table.table, db);
   else
-    ret= table_scan_all_for_i_s(thd, schema_table, event_table);
+    ret= table_scan_all_for_i_s(thd, schema_table, event_table.table);
 
-  close_thread_tables(thd);
+  close_system_tables(thd, &open_tables_backup);
 
   DBUG_PRINT("info", ("Return code=%d", ret));
   DBUG_RETURN(ret);
@@ -584,10 +587,7 @@ Event_db_repository::open_event_table(THD *thd, enum thr_lock_type lock_type,
   tables.init_one_table("mysql", 5, "event", 5, "event", lock_type);
 
   if (open_and_lock_tables(thd, &tables, FALSE, MYSQL_LOCK_IGNORE_TIMEOUT))
-  {
-    close_thread_tables(thd);
     DBUG_RETURN(TRUE);
-  }
 
   *table= tables.table;
   tables.table->use_all_columns();
@@ -700,7 +700,8 @@ Event_db_repository::create_event(THD *thd, Event_parse_data *parse_data,
 
 end:
   if (table)
-    close_thread_tables(thd);
+    close_mysql_tables(thd);
+
   thd->variables.sql_mode= saved_mode;
   DBUG_RETURN(test(ret));
 }
@@ -811,7 +812,8 @@ Event_db_repository::update_event(THD *thd, Event_parse_data *parse_data,
 
 end:
   if (table)
-    close_thread_tables(thd);
+    close_mysql_tables(thd);
+
   thd->variables.sql_mode= saved_mode;
   DBUG_RETURN(test(ret));
 }
@@ -865,7 +867,7 @@ Event_db_repository::drop_event(THD *thd, LEX_STRING db, LEX_STRING name,
 
 end:
   if (table)
-    close_thread_tables(thd);
+    close_mysql_tables(thd);
 
   DBUG_RETURN(test(ret));
 }
@@ -934,33 +936,13 @@ Event_db_repository::find_named_event(LEX_STRING db, LEX_STRING name,
 void
 Event_db_repository::drop_schema_events(THD *thd, LEX_STRING schema)
 {
-  DBUG_ENTER("Event_db_repository::drop_schema_events");
-  drop_events_by_field(thd, ET_FIELD_DB, schema);
-  DBUG_VOID_RETURN;
-}
-
-
-/**
-  Drops all events which have a specific value of a field.
-
-  @pre The thread handle has no open tables.
-
-  @param[in,out] thd         Thread
-  @param[in,out] table       mysql.event TABLE
-  @param[in]     field       Which field of the row to use for matching
-  @param[in]     field_value The value that should match
-*/
-
-void
-Event_db_repository::drop_events_by_field(THD *thd,
-                                          enum enum_events_table_field field,
-                                          LEX_STRING field_value)
-{
   int ret= 0;
   TABLE *table= NULL;
   READ_RECORD read_record_info;
-  DBUG_ENTER("Event_db_repository::drop_events_by_field");
-  DBUG_PRINT("enter", ("field=%d field_value=%s", field, field_value.str));
+  enum enum_events_table_field field= ET_FIELD_DB;
+  MDL_ticket *mdl_savepoint= thd->mdl_context.mdl_savepoint();
+  DBUG_ENTER("Event_db_repository::drop_schema_events");
+  DBUG_PRINT("enter", ("field=%d schema=%s", field, schema.str));
 
   if (open_event_table(thd, TL_WRITE, &table))
     DBUG_VOID_RETURN;
@@ -979,7 +961,7 @@ Event_db_repository::drop_events_by_field(THD *thd,
                           get_field(thd->mem_root,
                                     table->field[ET_FIELD_NAME])));
 
-      if (!sortcmp_lex_string(et_field_lex, field_value, system_charset_info))
+      if (!sortcmp_lex_string(et_field_lex, schema, system_charset_info))
       {
         DBUG_PRINT("info", ("Dropping"));
         if ((ret= table->file->ha_delete_row(table->record[0])))
@@ -989,6 +971,11 @@ Event_db_repository::drop_events_by_field(THD *thd,
   }
   end_read_record(&read_record_info);
   close_thread_tables(thd);
+  /*
+    Make sure to only release the MDL lock on mysql.event, not other
+    metadata locks DROP DATABASE might have acquired.
+  */
+  thd->mdl_context.rollback_to_savepoint(mdl_savepoint);
 
   DBUG_VOID_RETURN;
 }
@@ -1026,7 +1013,7 @@ Event_db_repository::load_named_event(THD *thd, LEX_STRING dbname,
     else if ((ret= etn->load_from_row(thd, table)))
       my_error(ER_CANNOT_LOAD_FROM_TABLE, MYF(0), "event");
 
-    close_thread_tables(thd);
+    close_mysql_tables(thd);
   }
 
   thd->variables.sql_mode= saved_mode;
@@ -1104,7 +1091,8 @@ update_timing_fields_for_event(THD *thd,
 
 end:
   if (table)
-    close_thread_tables(thd);
+    close_mysql_tables(thd);
+
   /* Restore the state of binlog format */
   DBUG_ASSERT(!thd->is_current_stmt_binlog_format_row());
   if (save_binlog_row_based)
@@ -1151,7 +1139,7 @@ Event_db_repository::check_system_tables(THD *thd)
     if (table_intact.check(tables.table, &mysql_db_table_def))
       ret= 1;
 
-    close_thread_tables(thd);
+    close_mysql_tables(thd);
   }
   /* Check mysql.user */
   tables.init_one_table("mysql", 5, "user", 4, "user", TL_READ);
@@ -1171,7 +1159,7 @@ Event_db_repository::check_system_tables(THD *thd)
                       event_priv_column_position);
       ret= 1;
     }
-    close_thread_tables(thd);
+    close_mysql_tables(thd);
   }
   /* Check mysql.event */
   tables.init_one_table("mysql", 5, "event", 5, "event", TL_READ);
@@ -1185,7 +1173,7 @@ Event_db_repository::check_system_tables(THD *thd)
   {
     if (table_intact.check(tables.table, &event_table_def))
       ret= 1;
-    close_thread_tables(thd);
+    close_mysql_tables(thd);
   }
 
   DBUG_RETURN(test(ret));