WL#3337 (Event scheduler new architecture)

This patch makes the relationship between Event_scheduler and Event_queue
unidirectional from the former to the latter.




The change is that the conditional on which the scheduler sleeped has been
moved to the Event_queue and the latter does not call anymore
Event_scheduler::queue_changed(), which in turn has be removed.


sql/event_queue.cc:
  Remove dependency of Event_queue on Event_scheduler but not vice versa.
  Event_scheduler polls whether there is time to execute an event.
  
  Removed notify_observers() as the way of calling has changed.
  Added Event_queue::cond_wait() similar to Event_scheduler::cond_wait().
sql/event_queue.h:
  init_queue() does not need anymore Event_scheduler object because
  the relationship is now one-way. Event_scheduler knows about Event_queue
  but not vice versa.
  
  get_top_execution_if_time() does by itself the waiting instead of
  returning abstime. This simplifies the code in Event_scheduler::run()
  get_top_execution_if_time() returns only if job_data != NULL or if
  the scheduler thread was killed.
  
  notify_observers() is no more used and therefore removed.
  
  Added Event_queue::cond_wait() because now there is waiting on a
  conditional variable in Event_queue too (like in Event_scheduler for
  ::stop()).
sql/event_scheduler.cc:
  Change the relationship between Event_scheduler & Event_queue.
  Event_queue does not know anymore about Event_scheduler. When
  the scheduler calls get_top_element_if_time() it may fall asleep
  on a conditional of Event_queue, if either the queue is empty or
  it's still not time for activation. When the method returns it
  will return a non-null address, namely an object to be executed.
  If the return value is NULL, the thread was killed by a call to
  Event_scheduler::stop() (we assert this).
sql/event_scheduler.h:
  Remove queue_changed() as it is obsoleted by making the relationship
  between Event_scheduler and Event_queue one-way, from the former to the
  latter. Event_queue now does not know about Event_scheduler.
  
  get_state() is changed to is_running(). The state enum should be private,
  as it is not needed to be seen from outside anymore.
sql/events.cc:
  Event_queue does not need anymore a pointer to Event_scheduler.

sql/event_queue.h

@@ -36,7 +36,7 @@ public:
   deinit_mutexes();
 
   bool
-  init_queue(THD *thd, Event_db_repository *db_repo, Event_scheduler *sched);
+  init_queue(THD *thd, Event_db_repository *db_repo);
   
   void
   deinit_queue();
@@ -60,8 +60,7 @@ public:
   recalculate_activation_times(THD *thd);
 
   bool
-  get_top_for_execution_if_time(THD *thd, time_t now, Event_job_data **job_data,
-                                struct timespec *abstime);
+  get_top_for_execution_if_time(THD *thd, Event_job_data **job_data);
   bool
   dump_internal_status(THD *thd);
 
@@ -80,14 +79,12 @@ protected:
   void
   empty_queue();
 
-  void
-  notify_observers();
-
   void
   dbug_dump_queue(time_t now);
 
   /* LOCK_event_queue is the mutex which protects the access to the queue. */
   pthread_mutex_t LOCK_event_queue;
+  pthread_cond_t COND_queue_state;
 
   Event_db_repository *db_repository;
 
@@ -96,6 +93,8 @@ protected:
   /* The sorted queue with the Event_job_data objects */
   QUEUE queue;
 
+  TIME next_activation_at;
+
   uint mutex_last_locked_at_line;
   uint mutex_last_unlocked_at_line;
   uint mutex_last_attempted_lock_at_line;
@@ -104,6 +103,7 @@ protected:
   const char* mutex_last_attempted_lock_in_func;
   bool mutex_queue_data_locked;
   bool mutex_queue_data_attempting_lock;
+  bool waiting_on_cond;
 
   /* helper functions for working with mutexes & conditionals */
   void
@@ -111,6 +111,10 @@ protected:
 
   void
   unlock_data(const char *func, uint line);
+
+  void
+  cond_wait(THD *thd, struct timespec *abstime, const char* msg,
+            const char *func, uint line);
 };
 
 #endif /* _EVENT_QUEUE_H_ */