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, 5 insertions, 3 deletions

diff --git a/sql/handler.cc b/sql/handler.cc
index 1518f2baaa0..88431d4db32 100644
--- a/sql/handler.cc
+++ b/sql/handler.cc
@@ -1300,7 +1300,10 @@ int ha_commit_trans(THD *thd, bool all)
   {
     /* Free resources and perform other cleanup even for 'empty' transactions. */
     if (is_real_trans)
+    {
       thd->transaction.cleanup();
+      thd->wakeup_subsequent_commits(error);
+    }
     DBUG_RETURN(0);
   }
 
@@ -1334,6 +1337,7 @@ int ha_commit_trans(THD *thd, bool all)
                                       thd->variables.lock_wait_timeout))
     {
       ha_rollback_trans(thd, all);
+      thd->wakeup_subsequent_commits(1);
       DBUG_RETURN(1);
     }
 
@@ -1421,6 +1425,7 @@ done:
 err:
   error= 1;                                  /* Transaction was rolled back */
   ha_rollback_trans(thd, all);
+  thd->wakeup_subsequent_commits(error);
 
 end:
   if (rw_trans && mdl_request.ticket)
@@ -1591,10 +1596,7 @@ int ha_rollback_trans(THD *thd, bool all)
 
   /* Always cleanup. Even if nht==0. There may be savepoints. */
   if (is_real_trans)
-  {
-    thd->wakeup_subsequent_commits(error);
     thd->transaction.cleanup();
-  }
   if (all)
     thd->transaction_rollback_request= FALSE;