Remove a race between Event Scheduler shutdown and SHOW PROCESSLIST.

This will hopefully fix events.test failure on vmware-win32, 
where scheduling is very primitive.


mysql-test/t/events_scheduling.test:
  This test case has no races now and can be enabled under valgrind.
sql/event_scheduler.cc:
  Make Event Scheduler thread shutdown more synchronous: report
  successful shutdown only after having removed the scheduler
  thread from the global list of threads.
  This ensures that after the scheduler has been stopped, its
  thread is not present in SHOW PROCESSLIST output.

mysql-test/t/events_scheduling.test

@@ -1,6 +1,5 @@
 # Can't test with embedded server that doesn't support grants
 -- source include/not_embedded.inc
--- source include/not_valgrind.inc
 
 CREATE DATABASE IF NOT EXISTS events_test;
 USE events_test;

sql/event_scheduler.cc

@@ -154,8 +154,6 @@ deinit_event_thread(THD *thd)
   thread_running--;
   delete thd;
   pthread_mutex_unlock(&LOCK_thread_count);
-
-  my_thread_end();
 }
 
 
@@ -231,8 +229,7 @@ event_scheduler_thread(void *arg)
   if (!res)
     scheduler->run(thd);
 
-  deinit_event_thread(thd);
+  my_thread_end();
-  pthread_exit(0);
   DBUG_RETURN(0);                               // Against gcc warnings
 }
 
@@ -260,6 +257,7 @@ event_worker_thread(void *arg)
   Event_worker_thread worker_thread;
   worker_thread.run(thd, event);
 
+  my_thread_end();
   return 0;                                     // Can't return anything here
 }
 
@@ -494,12 +492,14 @@ Event_scheduler::run(THD *thd)
     }
     DBUG_PRINT("info", ("state=%s", scheduler_states_names[state].str));
   }
+
   LOCK_DATA();
-  DBUG_PRINT("info", ("Signalling back to the stopper COND_state"));
+  deinit_event_thread(thd);
+  scheduler_thd= NULL;
   state= INITIALIZED;
+  DBUG_PRINT("info", ("Signalling back to the stopper COND_state"));
   pthread_cond_signal(&COND_state);
   UNLOCK_DATA();
-  sql_print_information("Event Scheduler: Stopped");
 
   DBUG_RETURN(res);
 }
@@ -651,17 +651,7 @@ Event_scheduler::stop()
     COND_STATE_WAIT(thd, NULL, "Waiting scheduler to stop");
   } while (state == STOPPING);
   DBUG_PRINT("info", ("Scheduler thread has cleaned up. Set state to INIT"));
-  /*
+  sql_print_information("Event Scheduler: Stopped");
-    The rationale behind setting it to NULL here but not destructing it
-    beforehand is because the THD will be deinited in event_scheduler_thread().
-    It's more clear when the post_init and the deinit is done in one function.
-    Here we just mark that the scheduler doesn't have a THD anymore. Though for
-    milliseconds the old thread could exist we can't use it anymore. When we
-    unlock the mutex in this function a little later the state will be
-    INITIALIZED. Therefore, a connection thread could enter the critical section
-    and will create a new THD object.
-  */
-  scheduler_thd= NULL;
 end:
   UNLOCK_DATA();
   DBUG_RETURN(FALSE);