Fix for bug#22740 Events: Decouple Event_queue from Event_db_repository

This patch implements the idea of the bug report by making Event_queue
unaware of Event_db_repository by making a higher level class - Events,
which is aware of most of all classes, responsible for passing all data
needed for adding/updating/deleting an event to/from the queue.

Introduces few new classes :
 - Event_worker_thread
 - Event_queue_element_for_exec


sql/event_data_objects.cc:
  Introduced a new class Event_queue_element_for_exec
  According to Konstantin it should be named Event_name and hold
  only two LEX_STRINGs but `dropped` is not saved on disk and will
  require additional logic in Event_worker_thread class, after loading
  to compute whether the event should be dropped or not. It's easier
  just to pass this flag around.
  
  Removed Event_queue_element::drop(). This method was a source of a
  race condition. At the place where the event should be dropped we
  call Events::drop_event() which is the only code-flow for dropping.
  In addition, because ::drop_event() holds Events::LOCK_metadata there is
  no source of race conditions. Before this patch dropping from ::drop()
  wasn't under LOCK_metadata and races were possible.
  
  Because Events::open_event_table was removed as a method, provisionally
  events_event_db_repository was exported from events.cc till a solution is
  build where Event_queue_element does not access directly mysql.event.
sql/event_data_objects.h:
  New class Event_queue_element_for_exec added which is returned
  from Event_queue::get_top_if_time() and passed through Event_scheduler
  to Event_worker_thread. There by using the (db)name Event_job_data is
  instanciated and executed.
  
  Dropped Event_queue_element::drop()
  
  thd was moved out of Event_job_data as it is now part of
  Event_queue_element_for_exec
sql/event_queue.cc:
  Removed dependency of Event_queue on Event_db_repository.
  The instantiation of Event_job_data was moved to class Event_worker_thread
  In place is a return of an object of Event_queue_element_for_exec is used
  later for instantiating Event_job_data.
  
  The `dropped` flag of Event_queue_element is passed over
  Event_queue_element_for_exec to the code in Event_worker_thread.
sql/event_queue.h:
  Removed dependency of Event_queue on Event_db_repository
  Removed dependency on Event_scheduler
sql/event_scheduler.cc:
  Added class Event_worker_thread, which is used during
  the execution of an event. It has a static init() method
  to get a pointer to Event_db_repository to be used for
  instantiation of Event_job_data object. This object it then
  executed.
sql/event_scheduler.h:
  Added class Event_worker_thread, which is used during
  the execution of an event.
sql/events.cc:
  Removed Events::open_event_table() because it was a product of
  a bad architecture.
sql/events.h:
  Removed friend definition, unneeded.
  
  Fixed Events::drop_event() to have the previous signature without
  bool only_from_disk
sql/sql_parse.cc:
  Fix call

sql/event_data_objects.cc

@@ -20,6 +20,8 @@
 #include "event_db_repository.h"
 #include "sp_head.h"
 
+/* That's a provisional solution */
+extern Event_db_repository events_event_db_repository;
 
 #define EVEX_MAX_INTERVAL_VALUE 1000000000L
 
@@ -30,6 +32,47 @@ event_change_security_context(THD *thd, LEX_STRING user, LEX_STRING host,
 static void
 event_restore_security_context(THD *thd, Security_context *backup);
 
+
+/*
+  Initiliazes dbname and name of an Event_queue_element_for_exec
+  object
+
+  SYNOPSIS
+    Event_queue_element_for_exec::init()
+
+  RETURN VALUE
+    FALSE  OK
+    TRUE   Error (OOM)
+*/
+
+bool
+Event_queue_element_for_exec::init(LEX_STRING db, LEX_STRING n)
+{
+  if (!(dbname.str= my_strndup(db.str, dbname.length= db.length, MYF(MY_WME))))
+    return TRUE;
+  if (!(name.str= my_strndup(n.str, name.length= n.length, MYF(MY_WME))))
+  {
+    my_free((gptr) dbname.str, MYF(0));
+    return TRUE;
+  }
+  return FALSE;
+}
+
+
+/*
+  Destructor
+
+  SYNOPSIS
+    Event_queue_element_for_exec::~Event_queue_element_for_exec()
+*/
+
+Event_queue_element_for_exec::~Event_queue_element_for_exec()
+{
+  my_free((gptr) dbname.str, MYF(0));
+  my_free((gptr) name.str, MYF(0));
+}
+
+
 /*
   Returns a new instance
 
@@ -743,7 +786,7 @@ Event_timed::~Event_timed()
 */
 
 Event_job_data::Event_job_data()
-  :thd(NULL), sphead(NULL), sql_mode(0)
+  :sphead(NULL), sql_mode(0)
 {
 }
 
@@ -1239,6 +1282,7 @@ Event_queue_element::compute_next_execution_time()
     DBUG_PRINT("info", ("Dropped: %d", dropped));
     status= Event_queue_element::DISABLED;
     status_changed= TRUE;
+    dropped= TRUE;
 
     goto ret;
   }
@@ -1446,32 +1490,6 @@ Event_queue_element::mark_last_executed(THD *thd)
 }
 
 
-/*
-  Drops the event
-
-  SYNOPSIS
-    Event_queue_element::drop()
-      thd   thread context
-
-  RETURN VALUE
-    0       OK
-   -1       Cannot open mysql.event
-   -2       Cannot find the event in mysql.event (already deleted?)
-
-   others   return code from SE in case deletion of the event row
-            failed.
-*/
-
-int
-Event_queue_element::drop(THD *thd)
-{
-  DBUG_ENTER("Event_queue_element::drop");
-
-  DBUG_RETURN(Events::get_instance()->
-                    drop_event(thd, dbname, name, FALSE, TRUE));
-}
-
-
 /*
   Saves status and last_executed_at to the disk if changed.
 
@@ -1503,13 +1521,13 @@ Event_queue_element::update_timing_fields(THD *thd)
 
   thd->reset_n_backup_open_tables_state(&backup);
 
-  if (Events::get_instance()->open_event_table(thd, TL_WRITE, &table))
+  if (events_event_db_repository.open_event_table(thd, TL_WRITE, &table))
   {
     ret= TRUE;
     goto done;
   }
   fields= table->field;
-  if ((ret= Events::get_instance()->db_repository->
+  if ((ret= events_event_db_repository.
                                  find_named_event(thd, dbname, name, table)))
     goto done;
 

sql/event_data_objects.h

@@ -27,6 +27,27 @@ class sp_head;
 class Sql_alloc;
 
 
+class Event_queue_element_for_exec
+{
+public:
+  Event_queue_element_for_exec(){};
+  ~Event_queue_element_for_exec();
+
+  bool
+  init(LEX_STRING dbname, LEX_STRING name);
+
+  LEX_STRING dbname;
+  LEX_STRING name;
+  bool dropped;
+  THD *thd;
+
+private:
+  /* Prevent use of these */
+  Event_queue_element_for_exec(const Event_queue_element_for_exec &);
+  void operator=(Event_queue_element_for_exec &);
+};
+
+
 class Event_basic
 {
 protected:
@@ -96,9 +117,6 @@ class Event_queue_element : public Event_basic
   bool
   compute_next_execution_time();
 
-  int
-  drop(THD *thd);
-
   void
   mark_last_executed(THD *thd);
 
@@ -160,7 +178,6 @@ class Event_timed : public Event_queue_element
 class Event_job_data : public Event_basic
 {
 public:
-  THD *thd;
   sp_head *sphead;
 
   LEX_STRING body;

sql/event_queue.h

@@ -16,12 +16,10 @@
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
 
 class Event_basic;
-class Event_db_repository;
-class Event_job_data;
 class Event_queue_element;
+class Event_queue_element_for_exec;
 
 class THD;
-class Event_scheduler;
 
 class Event_queue
 {
@@ -35,19 +33,19 @@ class Event_queue
   deinit_mutexes();
 
   bool
-  init_queue(THD *thd, Event_db_repository *db_repo);
+  init_queue(THD *thd);
   
   void
   deinit_queue();
 
   /* Methods for queue management follow */
 
-  int
-  create_event(THD *thd, LEX_STRING dbname, LEX_STRING name);
+  void
+  create_event(THD *thd, Event_queue_element *new_element);
 
-  int
+  void
   update_event(THD *thd, LEX_STRING dbname, LEX_STRING name,
-               LEX_STRING *new_schema, LEX_STRING *new_name);
+               Event_queue_element *new_element);
 
   void
   drop_event(THD *thd, LEX_STRING dbname, LEX_STRING name);
@@ -59,14 +57,15 @@ class Event_queue
   recalculate_activation_times(THD *thd);
 
   bool
-  get_top_for_execution_if_time(THD *thd, Event_job_data **job_data);
+  get_top_for_execution_if_time(THD *thd,
+                                Event_queue_element_for_exec **event_name);
+
 
   void
   dump_internal_status();
 
-  int
-  load_events_from_db(THD *thd);
-
+  void
+  empty_queue();
 protected:
   void
   find_n_remove_event(LEX_STRING db, LEX_STRING name);
@@ -76,8 +75,6 @@ class Event_queue
   drop_matching_events(THD *thd, LEX_STRING pattern,
                        bool (*)(LEX_STRING, Event_basic *));
 
-  void
-  empty_queue();
 
   void
   dbug_dump_queue(time_t now);
@@ -86,11 +83,7 @@ class Event_queue
   pthread_mutex_t LOCK_event_queue;
   pthread_cond_t COND_queue_state;
 
-  Event_db_repository *db_repository;
-
-  Event_scheduler *scheduler;
-
-  /* The sorted queue with the Event_job_data objects */
+  /* The sorted queue with the Event_queue_element objects */
   QUEUE queue;
 
   TIME next_activation_at;

sql/event_scheduler.cc

@@ -18,6 +18,7 @@
 #include "event_data_objects.h"
 #include "event_scheduler.h"
 #include "event_queue.h"
+#include "event_db_repository.h"
 
 #ifdef __GNUC__
 #if __GNUC__ >= 2
@@ -34,6 +35,11 @@
 
 extern pthread_attr_t connection_attrib;
 
+
+Event_db_repository *Event_worker_thread::db_repository;
+Events *Event_worker_thread::events_facade;
+
+
 static
 const LEX_STRING scheduler_states_names[] =
 {
@@ -60,8 +66,8 @@ struct scheduler_param {
       et   The event itself
 */
 
-static void
-evex_print_warnings(THD *thd, Event_job_data *et)
+void
+Event_worker_thread::print_warnings(THD *thd, Event_job_data *et)
 {
   MYSQL_ERROR *err;
   DBUG_ENTER("evex_print_warnings");
@@ -253,49 +259,97 @@ event_worker_thread(void *arg)
 {
   /* needs to be first for thread_stack */
   THD *thd; 
-  Event_job_data *event= (Event_job_data *)arg;
-  int ret;
+  Event_queue_element_for_exec *event= (Event_queue_element_for_exec *)arg;
 
   thd= event->thd;
-
   thd->thread_stack= (char *) &thd;             // remember where our stack is
-  DBUG_ENTER("event_worker_thread");
 
-  if (!post_init_event_thread(thd))
+  Event_worker_thread worker_thread;
+  worker_thread.run(thd, (Event_queue_element_for_exec *)arg);
+
+  deinit_event_thread(thd);
+
+  return 0;                                     // Can't return anything here
+}
+
+
+/*
+  Function that executes an event in a child thread. Setups the 
+  environment for the event execution and cleans after that.
+
+  SYNOPSIS
+    Event_worker_thread::run()
+      thd    Thread context
+      event  The Event_queue_element_for_exec object to be processed
+*/
+
+void
+Event_worker_thread::run(THD *thd, Event_queue_element_for_exec *event)
+{
+  int ret;
+  Event_job_data *job_data= NULL;
+  DBUG_ENTER("Event_worker_thread::run");
+  DBUG_PRINT("info", ("Baikonur, time is %d, BURAN reporting and operational."
+             "THD=0x%lx", time(NULL), thd));
+
+  if (post_init_event_thread(thd))
+    goto end;
+
+  if (!(job_data= new Event_job_data()))
+    goto end;
+  else if ((ret= db_repository->
+                  load_named_event(thd, event->dbname, event->name, job_data)))
   {
-    DBUG_PRINT("info", ("Baikonur, time is %ld, BURAN reporting and operational."
-                        "THD: 0x%lx",
-                        (long) time(NULL), (long) thd));
+    DBUG_PRINT("error", ("Got %d from load_named_event", ret));
+    goto end;
+  }
 
-    sql_print_information("SCHEDULER: [%s.%s of %s] executing in thread %lu. "
-                          "Execution %u",
-                          event->dbname.str, event->name.str,
-                          event->definer.str, thd->thread_id,
-                          event->execution_count);
+  sql_print_information("SCHEDULER: [%s.%s of %s] executing in thread %lu. ",
+                        job_data->dbname.str, job_data->name.str,
+                        job_data->definer.str, thd->thread_id);
 
   thd->enable_slow_log= TRUE;
 
-    ret= event->execute(thd);
+  ret= job_data->execute(thd);
 
-    evex_print_warnings(thd, event);
+  print_warnings(thd, job_data);
 
   sql_print_information("SCHEDULER: [%s.%s of %s] executed in thread %lu. "
-                          "RetCode=%d", event->dbname.str, event->name.str,
-                          event->definer.str, thd->thread_id, ret);
+                        "RetCode=%d", job_data->dbname.str, job_data->name.str,
+                        job_data->definer.str, thd->thread_id, ret);
   if (ret == EVEX_COMPILE_ERROR)
     sql_print_information("SCHEDULER: COMPILE ERROR for event %s.%s of %s",
-                            event->dbname.str, event->name.str,
-                            event->definer.str);
+                          job_data->dbname.str, job_data->name.str,
+                          job_data->definer.str);
   else if (ret == EVEX_MICROSECOND_UNSUP)
-      sql_print_information("SCHEDULER: MICROSECOND is not supported");
+end:
+  delete job_data;
+
+  if (event->dropped)
+  {
+    sql_print_information("SCHEDULER: Dropping %s.%s", event->dbname.str,
+                          event->name.str);
+    /*
+      Using db_repository can lead to a race condition because we access
+      the table without holding LOCK_metadata.
+      Scenario:
+      1. CREATE EVENT xyz AT ...    (conn thread)
+      2. execute xyz                (worker)
+      3. CREATE EVENT XYZ EVERY ... (conn thread)
+      4. drop xyz                   (worker)
+      5. XYZ was just created on disk but `drop xyz` of the worker dropped it.
+         A consequent load to create Event_queue_element will fail.
+
+      If all operations are performed under LOCK_metadata there is no such
+      problem. However, this comes at the price of introduction bi-directional
+      association between class Events and class Event_worker_thread.
+    */
+    events_facade->drop_event(thd, event->dbname, event->name, FALSE);
   }
   DBUG_PRINT("info", ("BURAN %s.%s is landing!", event->dbname.str,
              event->name.str));
-  delete event;
 
-  deinit_event_thread(thd);
-
-  DBUG_RETURN(0);                               // Can't return anything here
+  delete event;
 }
 
 
@@ -441,7 +495,6 @@ bool
 Event_scheduler::run(THD *thd)
 {
   int res= FALSE;
-  Event_job_data *job_data;
   DBUG_ENTER("Event_scheduler::run");
 
   sql_print_information("SCHEDULER: Manager thread started with id %lu",
@@ -454,18 +507,20 @@ Event_scheduler::run(THD *thd)
 
   while (is_running())
   {
+    Event_queue_element_for_exec *event_name;
+
     /* Gets a minimized version */
-    if (queue->get_top_for_execution_if_time(thd, &job_data))
+    if (queue->get_top_for_execution_if_time(thd, &event_name))
     {
       sql_print_information("SCHEDULER: Serious error during getting next "
                             "event to execute. Stopping");
       break;
     }
 
-    DBUG_PRINT("info", ("get_top returned job_data: 0x%lx", (long) job_data));
-    if (job_data)
+    DBUG_PRINT("info", ("get_top returned job_data=0x%lx", event_name));
+    if (event_name)
     {
-      if ((res= execute_top(thd, job_data)))
+      if ((res= execute_top(thd, event_name)))
         break;
     }
     else
@@ -499,7 +554,7 @@ Event_scheduler::run(THD *thd)
 */
 
 bool
-Event_scheduler::execute_top(THD *thd, Event_job_data *job_data)
+Event_scheduler::execute_top(THD *thd, Event_queue_element_for_exec *event_name)
 {
   THD *new_thd;
   pthread_t th;
@@ -510,13 +565,13 @@ Event_scheduler::execute_top(THD *thd, Event_job_data *job_data)
 
   pre_init_event_thread(new_thd);
   new_thd->system_thread= SYSTEM_THREAD_EVENT_WORKER;
-  job_data->thd= new_thd;
+  event_name->thd= new_thd;
   DBUG_PRINT("info", ("BURAN %s@%s ready for start t-3..2..1..0..ignition",
-             job_data->dbname.str, job_data->name.str));
+             event_name->dbname.str, event_name->name.str));
 
   /* Major failure */
   if ((res= pthread_create(&th, &connection_attrib, event_worker_thread,
-                           job_data)))
+                           event_name)))
     goto error;
 
   ++started_events;
@@ -537,7 +592,7 @@ Event_scheduler::execute_top(THD *thd, Event_job_data *job_data)
     delete new_thd;
     pthread_mutex_unlock(&LOCK_thread_count);
   }
-  delete job_data;
+  delete event_name;
   DBUG_RETURN(TRUE);
 }
 

sql/event_scheduler.h

@@ -15,8 +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 Event_queue;
 class Event_job_data;
+class Event_db_repository;
+class Events;
 
 void
 pre_init_event_thread(THD* thd);
@@ -27,6 +30,29 @@ post_init_event_thread(THD* thd);
 void
 deinit_event_thread(THD *thd);
 
+
+class Event_worker_thread 
+{
+public:
+  static void
+  init(Events *events, Event_db_repository *db_repo)
+  {
+    db_repository= db_repo;
+    events_facade= events;
+  }
+
+  void
+  run(THD *thd, Event_queue_element_for_exec *event);
+
+private:
+  void
+  print_warnings(THD *thd, Event_job_data *et);
+
+  static Event_db_repository *db_repository;
+  static Events *events_facade;
+};
+
+
 class Event_scheduler
 {
 public:
@@ -71,10 +97,9 @@ class Event_scheduler
   uint
   workers_count();
 
-
   /* helper functions */
   bool
-  execute_top(THD *thd, Event_job_data *job_data);
+  execute_top(THD *thd, Event_queue_element_for_exec *event_name);
 
   /* helper functions for working with mutexes & conditionals */
   void

sql/events.cc

@@ -97,7 +97,7 @@ Event_queue events_event_queue;
 static
 Event_scheduler events_event_scheduler;
 
-static
+
 Event_db_repository events_event_db_repository;
 
 Events Events::singleton;
@@ -295,29 +295,6 @@ Events::Events()
 }
 
 
-/*
-  Opens mysql.event table with specified lock
-
-  SYNOPSIS
-    Events::open_event_table()
-    thd         Thread context
-    lock_type   How to lock the table
-    table       We will store the open table here
-
-  RETURN VALUE
-    1   Cannot lock table
-    2   The table is corrupted - different number of fields
-    0   OK
-*/
-
-int
-Events::open_event_table(THD *thd, enum thr_lock_type lock_type,
-                         TABLE **table)
-{
-  return db_repository->open_event_table(thd, lock_type, table);
-}
-
-
 /*
   The function exported to the world for creating of events.
 
@@ -351,16 +328,24 @@ Events::create_event(THD *thd, Event_parse_data *parse_data, bool if_not_exists)
   /* On error conditions my_error() is called so no need to handle here */
   if (!(ret= db_repository->create_event(thd, parse_data, if_not_exists)))
   {
-    if ((ret= event_queue->create_event(thd, parse_data->dbname,
-                                        parse_data->name)))
+    Event_queue_element *new_element;
+
+    if (!(new_element= new Event_queue_element()))
+      ret= TRUE;                                // OOM
+    else if ((ret= db_repository->load_named_event(thd, parse_data->dbname,
+                                                   parse_data->name,
+                                                   new_element)))
     {
       DBUG_ASSERT(ret == OP_LOAD_ERROR);
-      my_error(ER_EVENT_MODIFY_QUEUE_ERROR, MYF(0));
+      delete new_element;
     }
+    else
+      event_queue->create_event(thd, new_element);
   }
   pthread_mutex_unlock(&LOCK_event_metadata);
 
   DBUG_RETURN(ret);
+  
 }
 
 
@@ -387,6 +372,7 @@ bool
 Events::update_event(THD *thd, Event_parse_data *parse_data, sp_name *rename_to)
 {
   int ret;
+  Event_queue_element *new_element;
   DBUG_ENTER("Events::update_event");
   LEX_STRING *new_dbname= rename_to ? &rename_to->m_db : NULL;
   LEX_STRING *new_name= rename_to ? &rename_to->m_name : NULL;
@@ -400,12 +386,20 @@ Events::update_event(THD *thd, Event_parse_data *parse_data, sp_name *rename_to)
   /* On error conditions my_error() is called so no need to handle here */
   if (!(ret= db_repository->update_event(thd, parse_data, new_dbname, new_name)))
   {
-    if ((ret= event_queue->update_event(thd, parse_data->dbname,
-                                        parse_data->name, new_dbname, new_name)))
+    LEX_STRING dbname= new_dbname ? *new_dbname : parse_data->dbname;
+    LEX_STRING name= new_name ? *new_name : parse_data->name;
+
+    if (!(new_element= new Event_queue_element()))
+      ret= TRUE;                                // OOM
+    else if ((ret= db_repository->load_named_event(thd, dbname, name,
+                                                   new_element)))
     {
       DBUG_ASSERT(ret == OP_LOAD_ERROR);
-      my_error(ER_EVENT_MODIFY_QUEUE_ERROR, MYF(0));
+      delete new_element;   
     }
+    else
+      event_queue->update_event(thd, parse_data->dbname, parse_data->name,
+                                new_element);
   }
   pthread_mutex_unlock(&LOCK_event_metadata);
 
@@ -423,10 +417,6 @@ Events::update_event(THD *thd, Event_parse_data *parse_data, sp_name *rename_to)
       name            [in]  Event's name
       if_exists       [in]  When set and the event does not exist =>
                             warning onto the stack
-      only_from_disk  [in]  Whether to remove the event from the queue too.
-                            In case of Event_job_data::drop() it's needed to
-                            do only disk drop because Event_queue will handle
-                            removal from memory queue.
 
   RETURN VALUE
     FALSE  OK
@@ -434,8 +424,7 @@ Events::update_event(THD *thd, Event_parse_data *parse_data, sp_name *rename_to)
 */
 
 bool
-Events::drop_event(THD *thd, LEX_STRING dbname, LEX_STRING name, bool if_exists,
-                   bool only_from_disk)
+Events::drop_event(THD *thd, LEX_STRING dbname, LEX_STRING name, bool if_exists)
 {
   int ret;
   DBUG_ENTER("Events::drop_event");
@@ -448,10 +437,7 @@ Events::drop_event(THD *thd, LEX_STRING dbname, LEX_STRING name, bool if_exists,
   pthread_mutex_lock(&LOCK_event_metadata);
   /* On error conditions my_error() is called so no need to handle here */
   if (!(ret= db_repository->drop_event(thd, dbname, name, if_exists)))
-  {
-    if (!only_from_disk)
     event_queue->drop_event(thd, dbname, name);
-  }
   pthread_mutex_unlock(&LOCK_event_metadata);
   DBUG_RETURN(ret);
 }
@@ -655,11 +641,12 @@ Events::init()
   }
   check_system_tables_error= FALSE;
 
-  if (event_queue->init_queue(thd, db_repository))
+  if (event_queue->init_queue(thd) || load_events_from_db(thd))
   {
     sql_print_error("SCHEDULER: Error while loading from disk.");
     goto end;
   }
+
   scheduler->init_scheduler(event_queue);
 
   DBUG_ASSERT(opt_event_scheduler == Events::EVENTS_ON ||
@@ -667,6 +654,7 @@ Events::init()
   if (opt_event_scheduler == Events::EVENTS_ON)
     res= scheduler->start();
 
+  Event_worker_thread::init(this, db_repository);
 end:
   delete thd;
   /* Remember that we don't have a THD */
@@ -903,3 +891,131 @@ Events::check_system_tables(THD *thd)
 
   DBUG_RETURN(ret);
 }
+
+
+/*
+  Loads all ENABLED events from mysql.event into the prioritized
+  queue. Called during scheduler main thread initialization. Compiles
+  the events. Creates Event_queue_element instances for every ENABLED event
+  from mysql.event.
+
+  SYNOPSIS
+    Events::load_events_from_db()
+      thd  Thread context. Used for memory allocation in some cases.
+
+  RETURN VALUE
+    0  OK
+   !0  Error (EVEX_OPEN_TABLE_FAILED, EVEX_MICROSECOND_UNSUP, 
+              EVEX_COMPILE_ERROR) - in all these cases mysql.event was
+              tampered.
+
+  NOTES
+    Reports the error to the console
+*/
+
+int
+Events::load_events_from_db(THD *thd)
+{
+  TABLE *table;
+  READ_RECORD read_record_info;
+  int ret= -1;
+  uint count= 0;
+  bool clean_the_queue= TRUE;
+
+  DBUG_ENTER("Events::load_events_from_db");
+  DBUG_PRINT("enter", ("thd=0x%lx", thd));
+
+  if ((ret= db_repository->open_event_table(thd, TL_READ, &table)))
+  {
+    sql_print_error("SCHEDULER: Table mysql.event is damaged. Can not open");
+    DBUG_RETURN(EVEX_OPEN_TABLE_FAILED);
+  }
+
+  init_read_record(&read_record_info, thd, table ,NULL,1,0);
+  while (!(read_record_info.read_record(&read_record_info)))
+  {
+    Event_queue_element *et;
+    if (!(et= new Event_queue_element))
+    {
+      DBUG_PRINT("info", ("Out of memory"));
+      break;
+    }
+    DBUG_PRINT("info", ("Loading event from row."));
+
+    if ((ret= et->load_from_row(table)))
+    {
+      sql_print_error("SCHEDULER: Error while loading from mysql.event. "
+                      "Table probably corrupted");
+      break;
+    }
+    if (et->status != Event_queue_element::ENABLED)
+    {
+      DBUG_PRINT("info",("%s is disabled",et->name.str));
+      delete et;
+      continue;
+    }
+
+    /* let's find when to be executed */
+    if (et->compute_next_execution_time())
+    {
+      sql_print_error("SCHEDULER: Error while computing execution time of %s.%s."
+                      " Skipping", et->dbname.str, et->name.str);
+      continue;
+    }
+
+    {
+      Event_job_data temp_job_data;
+      DBUG_PRINT("info", ("Event %s loaded from row. ", et->name.str));
+
+      temp_job_data.load_from_row(table);
+
+      /*
+        We load only on scheduler root just to check whether the body
+        compiles.
+      */
+      switch (ret= temp_job_data.compile(thd, thd->mem_root)) {
+      case EVEX_MICROSECOND_UNSUP:
+        sql_print_error("SCHEDULER: mysql.event is tampered. MICROSECOND is not "
+                        "supported but found in mysql.event");
+        break;
+      case EVEX_COMPILE_ERROR:
+        sql_print_error("SCHEDULER: Error while compiling %s.%s. Aborting load",
+                        et->dbname.str, et->name.str);
+        break;
+      default:
+        break;
+      }
+      thd->end_statement();
+      thd->cleanup_after_query();
+    }
+    if (ret)
+    {
+      delete et;
+      goto end;
+    }
+
+    DBUG_PRINT("load_events_from_db", ("Adding 0x%lx to the exec list."));
+    event_queue->create_event(thd, et);
+    count++;
+  }
+  clean_the_queue= FALSE;
+end:
+  end_read_record(&read_record_info);
+
+  if (clean_the_queue)
+  {
+    event_queue->empty_queue();
+    ret= -1;
+  }
+  else
+  {
+    ret= 0;
+    sql_print_information("SCHEDULER: Loaded %d event%s", count,
+                          (count == 1)?"":"s");
+  }
+
+  close_thread_tables(thd);
+
+  DBUG_PRINT("info", ("Status code %d. Loaded %d event(s)", ret, count));
+  DBUG_RETURN(ret);
+}

sql/events.h

@@ -42,13 +42,6 @@ sortcmp_lex_string(LEX_STRING s, LEX_STRING t, CHARSET_INFO *cs);
 class Events
 {
 public:
-  /*
-    Quite NOT the best practice and will be removed once
-    Event_timed::drop() and Event_timed is fixed not do drop directly
-    or other scheme will be found.
-  */
-  friend class Event_queue_element;
-  
   /* The order should match the order in opt_typelib */
   enum enum_opt_event_scheduler
   {
@@ -92,15 +85,11 @@ class Events
   update_event(THD *thd, Event_parse_data *parse_data, sp_name *rename_to);
 
   bool
-  drop_event(THD *thd, LEX_STRING dbname, LEX_STRING name, bool if_exists,
-             bool only_from_disk);
+  drop_event(THD *thd, LEX_STRING dbname, LEX_STRING name, bool if_exists);
 
   void
   drop_schema_events(THD *thd, char *db);
 
-  int
-  open_event_table(THD *thd, enum thr_lock_type lock_type, TABLE **table);
-
   bool
   show_create_event(THD *thd, LEX_STRING dbname, LEX_STRING name);
 
@@ -119,6 +108,9 @@ class Events
   bool
   check_system_tables(THD *thd);
 
+  int
+  load_events_from_db(THD *thd);
+
   /* Singleton DP is used */
   Events();
   ~Events(){}

sql/sql_parse.cc

@@ -4047,8 +4047,7 @@ mysql_execute_command(THD *thd)
       if (!(res= Events::get_instance()->drop_event(thd,
                                                     lex->spname->m_db,
                                                     lex->spname->m_name,
-                                                    lex->drop_if_exists,
-                                                    FALSE)))
+                                                    lex->drop_if_exists)))
         send_ok(thd);
     }
     break;