MDEV-13472 rpl.rpl_semi_sync_wait_point crashes because of thd_destructor_proxy

InnoDB: in slow shutodwn mode do not stop purge threads
as long as some connection threads are running

mysql-test/suite/innodb/r/purge_thread_shutdown.result

+connect con1, localhost, root;
 create table t1 (a int) engine=innodb;
 insert t1 values (1),(2),(3),(4);
 delete from t1 where a=1;
 select user,state from information_schema.processlist order by 2;
 user	state
+root	
 root	Filling schema table
 system user	InnoDB purge coordinator
 system user	InnoDB purge worker
@@ -10,10 +12,22 @@ system user	InnoDB purge worker
 system user	InnoDB purge worker
 system user	InnoDB shutdown handler
 set global debug_dbug='+d,only_kill_system_threads';
-connect con1, localhost, root;
+set global innodb_fast_shutdown=0;
 shutdown;
 connection default;
 disconnect con1;
+select user,state from information_schema.processlist order by 2;
+user	state
+root	Filling schema table
+system user	InnoDB purge coordinator
+system user	InnoDB purge worker
+system user	InnoDB purge worker
+system user	InnoDB purge worker
+system user	InnoDB slow shutdown wait
+set global innodb_fast_shutdown=1;
+select user,state from information_schema.processlist order by 2;
+user	state
+root	Filling schema table
 delete from t1 where a=3;
 set global innodb_fast_shutdown=0;
 ERROR 42000: Variable 'innodb_fast_shutdown' can't be set to the value of '0'

mysql-test/suite/innodb/t/purge_thread_shutdown.test

@@ -2,6 +2,7 @@ source include/have_innodb.inc;
 source include/not_embedded.inc;
 source include/have_debug.inc;
 
+connect con1, localhost, root;
 create table t1 (a int) engine=innodb;
 insert t1 values (1),(2),(3),(4);
 delete from t1 where a=1;
@@ -9,8 +10,7 @@ delete from t1 where a=1;
 select user,state from information_schema.processlist order by 2;
 
 set global debug_dbug='+d,only_kill_system_threads';
-
-connect con1, localhost, root;
+set global innodb_fast_shutdown=0;
 
 let $_server_id= `SELECT @@server_id`;
 let $_expect_file_name= $MYSQLTEST_VARDIR/tmp/mysqld.$_server_id.expect;
@@ -20,11 +20,16 @@ send shutdown;
 connection default;
 disconnect con1;
 
+sleep 5;
+select user,state from information_schema.processlist order by 2;
+set global innodb_fast_shutdown=1;
+
 let $wait_condition=select count(*) = 0 from information_schema.processlist where user='system user';
 source include/wait_condition.inc;
+select user,state from information_schema.processlist order by 2;
 
 delete from t1 where a=3;
---error ER_WRONG_VALUE_FOR_VAR
+error ER_WRONG_VALUE_FOR_VAR;
 set global innodb_fast_shutdown=0;
 
 let $me=`select connection_id()`;

storage/innobase/handler/ha_innodb.cc

@@ -351,10 +351,11 @@ thd_destructor_proxy(void *)
 	mysql_mutex_unlock(&thd_destructor_mutex);
 	srv_running = NULL;
 
-	if (srv_fast_shutdown == 0) {
-		while (trx_sys_any_active_transactions()) {
-			os_thread_sleep(1000);
-		}
+	while (srv_fast_shutdown == 0 &&
+	       (trx_sys_any_active_transactions() ||
+		(uint)thread_count > srv_n_purge_threads + 1)) {
+		thd_proc_info(thd, "InnoDB slow shutdown wait");
+		os_thread_sleep(1000);
 	}
 
 	/* Some background threads might generate undo pages that will