MDEV-17062 : Test failure on galera.MW-336

Add mutex protection while we calculate required slave
thread change and create them. Add error handling.

1 files changed, 9 insertions, 2 deletions

diff --git a/sql/wsrep_var.cc b/sql/wsrep_var.cc
index 315cfe2c53e..5f76f650b34 100644
--- a/sql/wsrep_var.cc
+++ b/sql/wsrep_var.cc
@@ -594,15 +594,22 @@ static void wsrep_slave_count_change_update ()
 
 bool wsrep_slave_threads_update (sys_var *self, THD* thd, enum_var_type type)
 {
+  mysql_mutex_lock(&LOCK_wsrep_slave_threads);
+  bool res= false;
+
   wsrep_slave_count_change_update();
+
   if (wsrep_slave_count_change > 0)
   {
     WSREP_DEBUG("Creating %d applier threads, total %ld", wsrep_slave_count_change, wsrep_slave_threads);
-    wsrep_create_appliers(wsrep_slave_count_change);
+    res= wsrep_create_appliers(wsrep_slave_count_change, true);
     WSREP_DEBUG("Running %lu applier threads", wsrep_running_applier_threads);
     wsrep_slave_count_change = 0;
   }
-  return false;
+
+  mysql_mutex_unlock(&LOCK_wsrep_slave_threads);
+
+  return res;
 }
 
 bool wsrep_desync_check (sys_var *self, THD* thd, set_var* var)