BUG#16420: Events: timestamps become UTC

BUG#26429: SHOW CREATE EVENT is incorrect for an event that
           STARTS NOW()
BUG#26431: Impossible to re-create an event from backup if its
           STARTS clause is in the past
WL#3698: Events: execution in local time zone

The problem was that local times specified by the user in AT, STARTS
and ENDS of CREATE EVENT/ALTER EVENT statement were converted to UTC,
and the original time zone was forgotten.  This way, event scheduler
couldn't honor Daylight Saving Time shifts, and times shown to the
user were also in UTC.  Additionally, CREATE EVENT didn't allow times
in the past, thus preventing straightforward event restoration from
old backups.

This patch reworks event scheduler time computations, performing them
in the time zone associated with the event.  Also it allows times to
be in the past.

The patch adds time_zone column to mysql.event table.

NOTE: The patch is almost final, but the bug#9953 should be pushed
first.

1 files changed, 22 insertions, 21 deletions

diff --git a/sql/event_queue.cc b/sql/event_queue.cc
index 296c30506f6..bcfe0a222f1 100644
--- a/sql/event_queue.cc
+++ b/sql/event_queue.cc
@@ -65,8 +65,13 @@ struct event_queue_param
 static int 
 event_queue_element_compare_q(void *vptr, byte* a, byte *b)
 {
-  return my_time_compare(&((Event_queue_element *)a)->execute_at,
-                         &((Event_queue_element *)b)->execute_at);
+  /*
+    Note that no overflow is possible here because both values are
+    non-negative, and subtraction is done in the signed my_time_t
+    type.
+  */
+  return (((Event_queue_element *)a)->execute_at
+          - ((Event_queue_element *)b)->execute_at);
 }
 
 
@@ -84,7 +89,7 @@ Event_queue::Event_queue()
 {
   mutex_last_unlocked_in_func= mutex_last_locked_in_func=
     mutex_last_attempted_lock_in_func= "";
-  set_zero_time(&next_activation_at, MYSQL_TIMESTAMP_DATETIME);
+  next_activation_at= 0;
 }
 
 
@@ -504,15 +509,11 @@ Event_queue::dbug_dump_queue(time_t now)
     DBUG_PRINT("info", ("exec_at: %lu  starts: %lu  ends: %lu  execs_so_far: %u  "
                         "expr: %ld  et.exec_at: %ld  now: %ld  "
                         "(et.exec_at - now): %d  if: %d",
-                        (long) TIME_to_ulonglong_datetime(&et->execute_at),
-                        (long) TIME_to_ulonglong_datetime(&et->starts),
-                        (long) TIME_to_ulonglong_datetime(&et->ends),
-                        et->execution_count,
-                        (long) et->expression,
-                        (long) (sec_since_epoch_TIME(&et->execute_at)),
-                        (long) now,
-                        (int) (sec_since_epoch_TIME(&et->execute_at) - now),
-                        sec_since_epoch_TIME(&et->execute_at) <= now));
+                        (long) et->execute_at, (long) et->starts,
+                        (long) et->ends, et->execution_count,
+                        (long) et->expression, (long) et->execute_at,
+                        (long) now, (int) (et->execute_at - now),
+                        et->execute_at <= now));
   }
   DBUG_VOID_RETURN;
 #endif
@@ -541,7 +542,6 @@ Event_queue::get_top_for_execution_if_time(THD *thd,
                 Event_queue_element_for_exec **event_name)
 {
   bool ret= FALSE;
-  struct timespec top_time;
   *event_name= NULL;
   DBUG_ENTER("Event_queue::get_top_for_execution_if_time");
 
@@ -560,7 +560,7 @@ Event_queue::get_top_for_execution_if_time(THD *thd,
     if (!queue.elements)
     {
       /* There are no events in the queue */
-      set_zero_time(&next_activation_at, MYSQL_TIMESTAMP_DATETIME);
+      next_activation_at= 0;
 
       /* Wait on condition until signaled. Release LOCK_queue while waiting. */
       cond_wait(thd, NULL, queue_empty_msg, SCHED_FUNC, __LINE__);
@@ -572,16 +572,16 @@ Event_queue::get_top_for_execution_if_time(THD *thd,
 
     thd->end_time(); /* Get current time */
 
-    time_t seconds_to_next_event= 
-      sec_since_epoch_TIME(&top->execute_at) - thd->query_start();
     next_activation_at= top->execute_at;
-    if (seconds_to_next_event > 0)
+    if (next_activation_at > thd->query_start())
     {
       /*
         Not yet time for top event, wait on condition with
         time or until signaled. Release LOCK_queue while waiting.
       */
-      set_timespec(top_time, seconds_to_next_event);
+      struct timespec top_time;
+      top_time.tv_sec= next_activation_at;
+      top_time.tv_nsec= 0;
       cond_wait(thd, &top_time, queue_wait_msg, SCHED_FUNC, __LINE__);
 
       continue;
@@ -759,10 +759,11 @@ Event_queue::dump_internal_status()
     printf("Last lock attempt at: %s:%u\n", mutex_last_attempted_lock_in_func,
                                             mutex_last_attempted_lock_at_line);
   printf("WOC             : %s\n", waiting_on_cond? "YES":"NO");
+
+  TIME time;
+  my_tz_UTC->gmt_sec_to_TIME(&time, next_activation_at);
   printf("Next activation : %04d-%02d-%02d %02d:%02d:%02d\n",
-         next_activation_at.year, next_activation_at.month,
-         next_activation_at.day, next_activation_at.hour,
-         next_activation_at.minute, next_activation_at.second);
+         time.year, time.month, time.day, time.hour, time.minute, time.second);
 
   DBUG_VOID_RETURN;
 }