MDEV-5363: Make parallel replication waits killable

Add a test case for killing a waiting query in parallel replication.

Fix several bugs found:

 - We should not wakeup_subsequent_commits() in ha_rollback_trans(), since we
   do not know the right wakeup_error() to give.

 - When a wait_for_prior_commit() is killed, we must unregister from the
   waitee so we do not race and get an extra (non-kill) wakeup.

 - We need to deal with error propagation correctly in queue_for_group_commit
   when one thread is killed.

 - Fix one locking issue in queue_for_group_commit(), we could unlock the
   waitee lock too early and this end up processing wakeup() with insufficient
   locking.

 - Fix Xid_log_event::do_apply_event; if commit fails it must not update the
   in-memory @@gtid_slave_pos state.

 - Fix and cleanup some things in the rpl_parallel.cc error handling.

 - Add a missing check for killed in the slave sql driver thread, to avoid a
   race.

1 files changed, 11 insertions, 0 deletions

diff --git a/sql/slave.cc b/sql/slave.cc
index 4be4a96d142..bddb69d84bb 100644
--- a/sql/slave.cc
+++ b/sql/slave.cc
@@ -6242,6 +6242,17 @@ static Log_event* next_event(rpl_group_info *rgi, ulonglong *event_size)
         }
 
         /*
+          We have to check sql_slave_killed() here an extra time.
+          Otherwise we may miss a wakeup, since last check was done
+          without holding LOCK_log.
+        */
+        if (sql_slave_killed(rgi))
+        {
+          mysql_mutex_unlock(log_lock);
+          break;
+        }
+
+        /*
           If the I/O thread is blocked, unblock it.  Ok to broadcast
           after unlock, because the mutex is only destroyed in
           ~Relay_log_info(), i.e. when rli is destroyed, and rli will