A set of changes aiming to make the Event Scheduler more user-friendly

when there are no up-to-date system tables to support it:
 - initialize the scheduler before reporting "Ready for connections".
   This ensures that warnings, if any, are printed before "Ready for
   connections", and this message is not mangled.
 - do not abort the scheduler if there are no system tables
 - check the tables once at start up, remember the status and disable
   the scheduler if the tables are not up to date.
   If one attempts to use the scheduler with bad tables,
   issue an error message.
 - clean up the behaviour of the module under LOCK TABLES and pre-locking
   mode
 - make sure implicit commit of Events DDL works as expected.
 - add more tests


Collateral clean ups in the events code.

This patch fixes Bug#23631 Events: SHOW VARIABLES doesn't work 
when mysql.event is damaged

1 files changed, 62 insertions, 44 deletions

diff --git a/sql/events.h b/sql/events.h
index f97a0c5f57e..db0e947ab6c 100644
--- a/sql/events.h
+++ b/sql/events.h
@@ -15,7 +15,11 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
 
-class sp_name;
+/*
+  @file
+  A public interface of Events Scheduler module.
+*/
+
 class Event_parse_data;
 class Event_db_repository;
 class Event_queue;
@@ -40,6 +44,22 @@ sortcmp_lex_string(LEX_STRING s, LEX_STRING t, CHARSET_INFO *cs);
 /**
   @class Events -- a facade to the functionality of the Event Scheduler.
 
+  Every public operation against the scheduler has to be executed via the
+  interface provided by a static method of this class. No instance of this
+  class is ever created and it has no non-static data members.
+
+  The life cycle of the Events module is the following:
+
+  At server start up:
+     set_opt_event_scheduler() -> init_mutexes() -> init()
+  When the server is running:
+     create_event(), drop_event(), start_or_stop_event_scheduler(), etc
+  At shutdown:
+     deinit(), destroy_mutexes().
+
+  The peculiar initialization and shutdown cycle is an adaptation to the
+  outside server startup/shutdown framework and mimics the rest of MySQL
+  subsystems (ACL, time zone tables, etc).
 */
 
 class Events
@@ -53,47 +73,48 @@ public:
     EVENTS_DISABLED= 4
   };
 
-  static enum_opt_event_scheduler opt_event_scheduler;
-  static TYPELIB opt_typelib;
-  static TYPELIB var_typelib;
+  /* Possible values of @@event_scheduler variable */
+  static const TYPELIB var_typelib;
 
-  bool
-  init();
+  static bool
+  set_opt_event_scheduler(char *argument);
 
-  void
-  deinit();
+  static const char *
+  get_opt_event_scheduler_str();
 
-  void
-  init_mutexes();
+  /* A hack needed for Event_queue_element */
+  static Event_db_repository *
+  get_db_repository() { return db_repository; }
 
-  void
-  destroy_mutexes();
+  static bool
+  init(my_bool opt_noacl);
 
-  bool
-  start_execution_of_events();
+  static void
+  deinit();
 
-  bool
-  stop_execution_of_events();
+  static void
+  init_mutexes();
 
-  bool
-  is_execution_of_events_started();
+  static void
+  destroy_mutexes();
 
-  static Events *
-  get_instance();
+  static bool
+  start_or_stop_event_scheduler(enum enum_opt_event_scheduler start_or_stop);
 
-  bool
+  static bool
   create_event(THD *thd, Event_parse_data *parse_data, bool if_exists);
 
-  bool
-  update_event(THD *thd, Event_parse_data *parse_data, sp_name *rename_to);
+  static bool
+  update_event(THD *thd, Event_parse_data *parse_data,
+               LEX_STRING *new_dbname, LEX_STRING *new_name);
 
-  bool
+  static bool
   drop_event(THD *thd, LEX_STRING dbname, LEX_STRING name, bool if_exists);
 
-  void
+  static void
   drop_schema_events(THD *thd, char *db);
 
-  bool
+  static bool
   show_create_event(THD *thd, LEX_STRING dbname, LEX_STRING name);
 
   /* Needed for both SHOW CREATE EVENT and INFORMATION_SCHEMA */
@@ -104,31 +125,28 @@ public:
   static int
   fill_schema_events(THD *thd, TABLE_LIST *tables, COND * /* cond */);
 
-  void
+  static void
   dump_internal_status();
 
 private:
-  bool
-  check_system_tables(THD *thd);
+  static bool check_if_system_tables_error();
 
-  int
+  static bool
   load_events_from_db(THD *thd);
 
-  /* Singleton DP is used */
-  Events();
-  ~Events(){}
-
-  /* Singleton instance */
-  static Events singleton;
-
-  Event_queue         *event_queue;
-  Event_scheduler     *scheduler;
-  Event_db_repository *db_repository;
-
-  pthread_mutex_t LOCK_event_metadata;
-
-  bool check_system_tables_error;
+private:
+  /* Command line option names */
+  static const TYPELIB opt_typelib;
+  static pthread_mutex_t LOCK_event_metadata;
+  static Event_queue         *event_queue;
+  static Event_scheduler     *scheduler;
+  static Event_db_repository *db_repository;
+  /* Current state of Event Scheduler */
+  static enum enum_opt_event_scheduler opt_event_scheduler;
+  /* Set to TRUE if an error at start up */
+  static bool check_system_tables_error;
 
+private:
   /* Prevent use of these */
   Events(const Events &);
   void operator=(Events &);