Race condition in slave SQL thread shutdown

  mysql_cond_broadcast(&rli->stop_cond);

  DBUG_EXECUTE_IF("simulate_slave_delay_at_terminate_bug38694", sleep(5););

  mysql_mutex_unlock(&rli->run_lock);  // tell the world we are done

  /*

    Deactivate the parallel replication thread pool, if there are now no more

    SQL threads running. Do this here, when we have released all locks, but

    while our THD (and current_thd) is still valid.

  */

  mysql_mutex_lock(&LOCK_active_mi);

  if (opt_slave_parallel_threads > 0 &&

      !master_info_index->any_slave_sql_running())

    rpl_parallel_inactivate_pool(&global_rpl_thread_pool);

  mysql_mutex_unlock(&LOCK_active_mi);

  mysql_mutex_lock(&LOCK_thread_count);

  THD_CHECK_SENTRY(thd);

  delete thd;

  mysql_mutex_unlock(&LOCK_thread_count);

diff --git a/sql/slave.cc b/sql/slave.cc

index 4129c4c..efc75f3 100644

--- a/sql/slave.cc

+++ b/sql/slave.cc

@@ -4837,6 +4837,7 @@ log '%s' at position %s, relay log '%s' position: %s%s", RPL_LOG_NAME,

   mysql_cond_broadcast(&rli->stop_cond);

   DBUG_EXECUTE_IF("simulate_slave_delay_at_terminate_bug38694", sleep(5););

   mysql_mutex_unlock(&rli->run_lock);  // tell the world we are done

+  sleep(1);

   /*

     Deactivate the parallel replication thread pool, if there are now no more

commit 682ed005c57dabb4615052a79789e44e5c93525c

Author: Kristian Nielsen <knielsen@knielsen-hq.org>

Date:   Wed Jun 10 11:57:42 2015 +0200

    MDEV-8294: Inconsistent behavior of slave parallel threads at runtime

    There were some cases where the slave SQL thread could stop without

    the pool of parallel replication worker threads being correctly

    de-activated.