fix for bug #17619 Scheduler race conditions

- Scheduler is either initialized at server start or never.
  Starting & stopping is now suspending & resuming.
- The scheduler has clear OO interface
- Now all calls to the scheduler are synchronous
- GLOBAL event_scheduler uses thd::sys_var_tmp (see set_var.cc)
- External API is encapsulated into class Events
- Includes fixes for all comments of Kostja's review of 19.05.2005

Starting to merge into 5.1-release (5.1.10) and push

1 files changed, 254 insertions, 0 deletions

diff --git a/sql/event_scheduler.h b/sql/event_scheduler.h
new file mode 100644
index 00000000000..e7bf4b633c5
--- /dev/null
+++ b/sql/event_scheduler.h
@@ -0,0 +1,254 @@
+#ifndef _EVENT_SCHEDULER_H_
+#define _EVENT_SCHEDULER_H_
+/* Copyright (C) 2004-2006 MySQL AB
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+
+
+class THD;
+typedef bool * (*event_timed_identifier_comparator)(Event_timed*, Event_timed*);
+
+int
+events_init();
+
+void
+events_shutdown();
+
+
+class Event_scheduler
+{
+public:
+  /* Return codes */
+  enum enum_error_code
+  {
+    OP_OK= 0,
+    OP_NOT_RUNNING,
+    OP_CANT_KILL,
+    OP_CANT_INIT,
+    OP_DISABLED_EVENT,
+    OP_LOAD_ERROR,
+    OP_ALREADY_EXISTS
+  };
+
+  enum enum_state
+  {
+    UNINITIALIZED= 0,
+    INITIALIZED,
+    COMMENCING,
+    CANTSTART,
+    RUNNING,
+    SUSPENDED,
+    IN_SHUTDOWN
+  };
+
+  enum enum_suspend_or_resume
+  {
+    SUSPEND= 1,
+    RESUME= 2
+  };
+
+  /* Singleton access */
+  static Event_scheduler*
+  get_instance();
+
+  /* Methods for queue management follow */
+
+  enum enum_error_code
+  add_event(THD *thd, Event_timed *et, bool check_existence);
+
+  bool
+  drop_event(THD *thd, Event_timed *et);
+
+  enum enum_error_code
+  replace_event(THD *thd, Event_timed *et, LEX_STRING *new_schema,
+                LEX_STRING *new_name);
+
+  int
+  drop_schema_events(THD *thd, LEX_STRING *schema);
+
+  int
+  drop_user_events(THD *thd, LEX_STRING *definer, uint *dropped_num)
+  { DBUG_ASSERT(0); return 0;}
+
+  uint
+  events_count();
+
+  /* State changing methods follow */
+
+  bool
+  start();
+
+  enum enum_error_code
+  stop();
+
+  bool
+  start_suspended();
+
+  bool
+  run(THD *thd);
+
+  enum enum_error_code
+  suspend_or_resume(enum enum_suspend_or_resume action);
+  
+  bool 
+  init();
+
+  void
+  destroy();
+
+  static void
+  init_mutexes();
+  
+  static void
+  destroy_mutexes();
+
+  void
+  report_error_during_start();
+
+  /* Information retrieving methods follow */
+
+  enum enum_state
+  get_state();
+
+  bool
+  initialized();
+
+  static int
+  dump_internal_status(THD *thd);
+
+  static bool
+  check_system_tables(THD *thd);
+
+private:
+  Event_timed *
+  find_event(Event_timed *etn, bool remove_from_q);
+
+  uint
+  workers_count();
+
+  bool
+  is_running_or_suspended();
+
+  /* helper functions */
+  bool
+  execute_top(THD *thd);
+
+  void
+  clean_queue(THD *thd);
+  
+  void
+  stop_all_running_events(THD *thd);
+
+  enum enum_error_code
+  load_event(THD *thd, Event_timed *etn, Event_timed **etn_new);
+
+  int
+  load_events_from_db(THD *thd);
+
+  void
+  drop_matching_events(THD *thd, LEX_STRING *pattern,
+                       bool (*)(Event_timed *,LEX_STRING *));
+
+  bool
+  check_n_suspend_if_needed(THD *thd);
+
+  bool
+  check_n_wait_for_non_empty_queue(THD *thd);
+
+  /* Singleton DP is used */
+  Event_scheduler();
+  
+  enum enum_cond_vars
+  {
+    COND_NONE= -1,
+    /*
+      COND_new_work is a conditional used to signal that there is a change
+      of the queue that should inform the executor thread that new event should
+      be executed sooner than previously expected, because of add/replace event.
+    */
+    COND_new_work= 0,
+    /*
+      COND_started is a conditional used to synchronize the thread in which 
+      ::start() was called and the spawned thread. ::start() spawns a new thread
+      and then waits on COND_started but also checks when awaken that `state` is
+      either RUNNING or CANTSTART. Then it returns back.
+    */
+    COND_started_or_stopped,
+    /*
+      Conditional used for signalling from the scheduler thread back to the
+      thread that calls ::suspend() or ::resume. Synchronizing the calls.
+    */
+    COND_suspend_or_resume,
+    /* Must be always last */
+    COND_LAST,
+  };
+
+  /* Singleton instance */
+  static Event_scheduler singleton;
+  
+  /* This is the current status of the life-cycle of the manager. */
+  enum enum_state state;
+
+  /* Set to start the scheduler in suspended state */
+  bool start_scheduler_suspended;
+
+  /*
+    LOCK_scheduler_data is the mutex which protects the access to the
+    manager's queue as well as used when signalling COND_new_work,
+    COND_started and COND_shutdown.
+  */
+  pthread_mutex_t LOCK_scheduler_data;
+
+  /*
+    Holds the thread id of the executor thread or 0 if the executor is not
+    running. It is used by ::shutdown() to know which thread to kill with
+    kill_one_thread(). The latter wake ups a thread if it is waiting on a
+    conditional variable and sets thd->killed to non-zero.
+  */
+  ulong thread_id;
+
+  pthread_cond_t cond_vars[COND_LAST];
+  static const char * const cond_vars_names[COND_LAST];
+
+  /* The MEM_ROOT of the object */
+  MEM_ROOT scheduler_root;
+
+  /* The sorted queue with the Event_timed objects */
+  QUEUE queue;
+  
+  uint mutex_last_locked_at_line;
+  uint mutex_last_unlocked_at_line;
+  const char* mutex_last_locked_in_func;
+  const char* mutex_last_unlocked_in_func;
+  enum enum_cond_vars cond_waiting_on;
+  bool mutex_scheduler_data_locked;
+
+  /* helper functions for working with mutexes & conditionals */
+  int
+  lock_data(const char *func, uint line);
+
+  int
+  unlock_data(const char *func, uint line);
+
+  int
+  cond_wait(enum enum_cond_vars, pthread_mutex_t *mutex);
+
+private:
+  /* Prevent use of these */
+  Event_scheduler(const Event_scheduler &);
+  void operator=(Event_scheduler &);
+};
+
+#endif /* _EVENT_SCHEDULER_H_ */