Optimize RUN_HOOK() call

RUN_HOOK() is only called if semisync is enabled

As the server can't disable the hooks if something is in progress, I added
a new variable, run_hooks_enabled, that is set the first time semi sync is
used. This means that RUN_HOOK will have no overhead, unless semi sync
master or slave has been enabled once.

Some of the changes was just to get rid of warnings for embedded server

sql/handler.cc

@@ -1484,7 +1484,7 @@ int ha_commit_trans(THD *thd, bool all)
   mysql_mutex_assert_not_owner(mysql_bin_log.get_log_lock());
   mysql_mutex_assert_not_owner(&LOCK_after_binlog_sync);
   mysql_mutex_assert_not_owner(&LOCK_commit_ordered);
-  RUN_HOOK(transaction, after_commit, (thd, FALSE));
+  (void) RUN_HOOK(transaction, after_commit, (thd, FALSE));
   goto end;
 
   /* Come here if error and we need to rollback. */

sql/log.cc

@@ -6374,11 +6374,9 @@ bool MYSQL_BIN_LOG::write(Log_event *event_info, my_bool *with_annotate)
           mysql_mutex_assert_owner(&LOCK_log);
           mysql_mutex_assert_not_owner(&LOCK_after_binlog_sync);
           mysql_mutex_assert_not_owner(&LOCK_commit_ordered);
-          bool first= true;
-          bool last= true;
           if ((error= RUN_HOOK(binlog_storage, after_flush,
                                (thd, log_file_name, file->pos_in_file,
-                                synced, first, last))))
+                                synced, true, true))))
           {
             sql_print_error("Failed to run 'after_flush' hooks");
             error= 1;
@@ -6408,11 +6406,9 @@ bool MYSQL_BIN_LOG::write(Log_event *event_info, my_bool *with_annotate)
       mysql_mutex_assert_not_owner(&LOCK_log);
       mysql_mutex_assert_owner(&LOCK_after_binlog_sync);
       mysql_mutex_assert_not_owner(&LOCK_commit_ordered);
-      bool first= true;
-      bool last= true;
       if (RUN_HOOK(binlog_storage, after_sync,
                    (thd, log_file_name, file->pos_in_file,
-                    first, last)))
+                    true, true)))
       {
         error=1;
         /* error is already printed inside hook */
@@ -7838,7 +7834,8 @@ MYSQL_BIN_LOG::trx_group_commit_leader(group_commit_entry *leader)
       mysql_mutex_assert_owner(&LOCK_log);
       mysql_mutex_assert_not_owner(&LOCK_after_binlog_sync);
       mysql_mutex_assert_not_owner(&LOCK_commit_ordered);
-      bool first= true, last;
+      bool first __attribute__((unused))= true;
+      bool last __attribute__((unused));
       for (current= queue; current != NULL; current= current->next)
       {
         last= current->next == NULL;
@@ -7924,7 +7921,8 @@ MYSQL_BIN_LOG::trx_group_commit_leader(group_commit_entry *leader)
     mysql_mutex_assert_owner(&LOCK_after_binlog_sync);
     mysql_mutex_assert_not_owner(&LOCK_commit_ordered);
 
-    bool first= true, last;
+    bool first __attribute__((unused))= true;
+    bool last __attribute__((unused));
     for (current= queue; current != NULL; current= current->next)
     {
       last= current->next == NULL;

sql/mysqld.cc

@@ -390,7 +390,7 @@ static longlong start_memory_used;
 /* Global variables */
 
 bool opt_bin_log, opt_bin_log_used=0, opt_ignore_builtin_innodb= 0;
-bool opt_bin_log_compress;
+bool opt_bin_log_compress, run_hooks_enabled;
 uint opt_bin_log_compress_min_len;
 my_bool opt_log, debug_assert_if_crashed_table= 0, opt_help= 0;
 my_bool debug_assert_on_not_freed_memory= 0;
@@ -8950,6 +8950,7 @@ static int mysql_init_variables(void)
   transactions_multi_engine= 0;
   rpl_transactions_multi_engine= 0;
   transactions_gtid_foreign_engine= 0;
+  run_hooks_enabled= 0;
   log_bin_basename= NULL;
   log_bin_index= NULL;
 

sql/mysqld.h

@@ -109,6 +109,7 @@ extern CHARSET_INFO *character_set_filesystem;
 extern MY_BITMAP temp_pool;
 extern bool opt_large_files;
 extern bool opt_update_log, opt_bin_log, opt_error_log, opt_bin_log_compress; 
+extern bool run_hooks_enabled;
 extern uint opt_bin_log_compress_min_len;
 extern my_bool opt_log, opt_bootstrap;
 extern my_bool opt_backup_history_log;

sql/rpl_handler.h

@@ -206,11 +206,13 @@ extern Binlog_relay_IO_delegate *binlog_relay_io_delegate;
 #endif /* HAVE_REPLICATION */
 
 /*
-  if there is no observers in the delegate, we can return 0
-  immediately.
+  if semisync replication is not enabled, we can return immediately.
 */
-#define RUN_HOOK(group, hook, args)             \
-  (group ##_delegate->is_empty() ?              \
-   0 : group ##_delegate->hook args)
+#ifdef HAVE_REPLICATION
+#define RUN_HOOK(group, hook, args)   \
+  (unlikely(run_hooks_enabled) ? group ##_delegate->hook args : 0)
+#else
+#define RUN_HOOK(group, hook, args) 0
+#endif /* HAVE_REPLICATION */
 
 #endif /* RPL_HANDLER_H */

sql/semisync_slave.h

@@ -44,6 +44,7 @@ class ReplSemiSyncSlave
     return slave_enabled_;
   }
   void setSlaveEnabled(bool enabled) {
+    run_hooks_enabled|= enabled;
     slave_enabled_ = enabled;
   }