fix for bug #19170 (Event creation leads to 100% CPU usage)

sql/event_timed.cc

@@ -731,7 +731,9 @@ bool get_next_time(TIME *next, TIME *start, TIME *time_now, TIME *last_exec,
       get the next exec if the modulus is not
     */
     DBUG_PRINT("info", ("multiplier=%d", multiplier));
-    if (seconds_diff % seconds || (!seconds_diff && last_exec->year))
+    if (seconds_diff % seconds || (!seconds_diff && last_exec->year) ||
+        TIME_to_ulonglong_datetime(time_now) ==
+          TIME_to_ulonglong_datetime(last_exec))
       ++multiplier;
     interval.second= seconds * multiplier;
     DBUG_PRINT("info", ("multiplier=%u interval.second=%u", multiplier,
@@ -893,16 +895,15 @@ Event_timed::compute_next_execution_time()
     DBUG_PRINT("info", ("Both STARTS & ENDS are set"));
     if (!last_executed.year)
     {
-      DBUG_PRINT("info", ("Not executed so far. Execute NOW."));
-      execute_at= time_now;
-      execute_at_null= FALSE;
+      DBUG_PRINT("info", ("Not executed so far."));
     }
-    else
+
     {
       TIME next_exec;
 
       DBUG_PRINT("info", ("Executed at least once"));
-      if (get_next_time(&next_exec, &starts, &time_now, &last_executed,
+      if (get_next_time(&next_exec, &starts, &time_now,
+                        last_executed.year? &last_executed:&starts,
                         expression, interval))
         goto err;
 
@@ -925,8 +926,9 @@ Event_timed::compute_next_execution_time()
     }
     goto ret;
   }
-  else if (starts_null && ends_null)
+  else if (starts_null && ends_null) 
   {
+    /* starts is always set, so this is a dead branch !! */
     DBUG_PRINT("info", ("Neither STARTS nor ENDS are set"));
     /*
       Both starts and m_ends are not set, so we schedule for the next
@@ -961,25 +963,26 @@ Event_timed::compute_next_execution_time()
         Hence schedule for starts + m_expression in case last_executed
         is not set, otherwise to last_executed + m_expression
       */
-      if (last_executed.year)
+      if (!last_executed.year)
+      {
+        DBUG_PRINT("info", ("Not executed so far."));
+      }
+
       {
         TIME next_exec;
         DBUG_PRINT("info", ("Executed at least once."));
-        if (get_next_time(&next_exec, &starts, &time_now, &last_executed,
+        if (get_next_time(&next_exec, &starts, &time_now, 
+                          last_executed.year? &last_executed:&starts,
                           expression, interval))
           goto err;
         execute_at= next_exec;
         DBUG_PRINT("info",("Next[%llu]",TIME_to_ulonglong_datetime(&next_exec)));
       }
-      else
-      {
-        DBUG_PRINT("info", ("Not executed so far. Execute at STARTS"));
-        execute_at= starts;
-      }
       execute_at_null= FALSE;
     }
     else
     {
+      /* this is a dead branch, because starts is always set !!! */
       DBUG_PRINT("info", ("STARTS is not set. ENDS is set"));
       /*
         - m_ends is set