MDEV-4506: Parallel replication: Intermediate commit.

A few fixes following tests. Now can apply one INSERT event in
a separate worker thread.

mysql-test/suite/rpl/t/rpl_parallel.test

+--source include/have_binlog_format_statement.inc
+
+connect (s1,127.0.0.1,root,,test,$MASTER_MYPORT,);
+connect (s2,127.0.0.1,root,,test,$SLAVE_MYPORT,);
+
+--connection s1
+SELECT @@server_id;
+SET sql_log_bin=0;
+CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=MyISAM;
+SET sql_log_bin=1;
+
+--connection s2
+SELECT @@server_id;
+SET sql_log_bin=0;
+CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=MyISAM;
+SET sql_log_bin=1;
+
+--replace_result $MASTER_MYPORT MASTER_PORT
+eval CHANGE MASTER TO master_host = '127.0.0.1', master_port = $MASTER_MYPORT,
+     master_user='root', master_use_gtid=current_pos;
+
+--connection s1
+INSERT INTO t1 VALUES (1);
+
+--connection s2
+query_vertical SHOW SLAVE STATUS;
+
+--source include/start_slave.inc
+SELECT * FROM t1;
+--sleep 1
+SELECT * FROM t1;
+
+--source include/stop_slave.inc
+
+--connection s1
+SET sql_log_bin=0;
+DROP TABLE t1;
+SET sql_log_bin=1;
+
+--connection s2
+RESET SLAVE ALL;
+SET sql_log_bin=0;
+DROP TABLE t1;
+SET sql_log_bin=1;

sql/rpl_parallel.cc

@@ -13,9 +13,13 @@ rpt_handle_event(rpl_parallel_thread::queued_event *qev,
                  struct rpl_parallel_thread *rpt)
 {
   int err;
+  Relay_log_info *rli= qev->rli;
 
+  thd->rli_slave= rli;
+  thd->rpl_filter = rli->mi->rpl_filter;
   /* ToDo: Access to thd, and what about rli, split out a parallel part? */
-  err= apply_event_and_update_pos(qev->ev, thd, qev->rli, rpt);
+  mysql_mutex_lock(&rli->data_lock);
+  err= apply_event_and_update_pos(qev->ev, thd, rli, rpt);
   /* ToDo: error handling. */
   /* ToDo: also free qev->ev, or hold on to it for a bit if necessary. */
 }
@@ -108,7 +112,7 @@ handle_rpl_parallel_thread(void *arg)
         }
       }
       rpt_handle_event(events, thd, rpt);
-      free(events);
+      my_free(events);
       events= next;
     }
 
@@ -313,6 +317,7 @@ rpl_parallel_thread_pool::destroy()
   rpl_parallel_change_thread_count(this, 0, true);
   mysql_mutex_destroy(&LOCK_rpl_thread_pool);
   mysql_cond_destroy(&COND_rpl_thread_pool);
+  inited= false;
 }
 
 
@@ -325,8 +330,8 @@ rpl_parallel_thread_pool::get_thread(rpl_parallel_entry *entry)
   while ((rpt= free_list) == NULL)
     mysql_cond_wait(&COND_rpl_thread_pool, &LOCK_rpl_thread_pool);
   free_list= rpt->next;
-  mysql_mutex_lock(&rpt->LOCK_rpl_thread);
   mysql_mutex_unlock(&LOCK_rpl_thread_pool);
+  mysql_mutex_lock(&rpt->LOCK_rpl_thread);
   rpt->current_entry= entry;
 
   return rpt;
@@ -383,6 +388,9 @@ rpl_parallel::do_event(Relay_log_info *rli, Log_event *ev, THD *parent_thd)
   rpl_parallel_thread *cur_thread;
   rpl_parallel_thread::queued_event *qev;
 
+  /* ToDo: what to do with this lock?!? */
+  mysql_mutex_unlock(&rli->data_lock);
+
   if (!(qev= (rpl_parallel_thread::queued_event *)my_malloc(sizeof(*qev),
                                                             MYF(0))))
   {

sql/slave.cc

@@ -5800,7 +5800,8 @@ static Log_event* next_event(Relay_log_info* rli)
                           llstr(my_b_tell(cur_log),llbuf1),
                           llstr(rli->event_relay_log_pos,llbuf2)));
       DBUG_ASSERT(my_b_tell(cur_log) >= BIN_LOG_HEADER_SIZE);
-      DBUG_ASSERT(my_b_tell(cur_log) == rli->event_relay_log_pos);
+      DBUG_ASSERT(opt_slave_parallel_threads > 0 ||
+                  my_b_tell(cur_log) == rli->event_relay_log_pos);
     }
 #endif
     /*