MDEV-32216 add tests for mariadb-dump --parallel

-  --parallel=N with or without --single-transaction
-  Error cases (too many connections, emulate error on one connection)
-  Windows specific test for named pipe connections

mysql-test/main/mariadb-dump-debug.result

@@ -0,0 +1,4 @@
+set @save_debug_dbug=@@global.debug_dbug;
+set global debug_dbug='+d,select_export_kill';
+mariadb-dump: Couldn't execute async query 'SELECT /*!40001 SQL_NO_CACHE */ `Host`, `User`, `Priv` INTO OUTFILE 'MYSQLTEST_VARDIR/tmp/global_priv.txt' /*!50138 CHARACTER SET binary */ FROM `mysql`.`global_priv`' (Query execution was interrupted)
+set global debug_dbug=@save_debug_dbug;

mysql-test/main/mariadb-dump-debug.test

@@ -0,0 +1,15 @@
+--source include/have_debug.inc
+--source include/not_embedded.inc
+# need to dump "mysql" schema
+--source include/have_innodb.inc
+
+# inject error on SELECT INTO OUTFILE
+set @save_debug_dbug=@@global.debug_dbug;
+set global debug_dbug='+d,select_export_kill';
+# This one succeeds
+--replace_result .\exe '' $MYSQLTEST_VARDIR MYSQLTEST_VARDIR
+--error 2
+--exec $MYSQL_DUMP --tab=$MYSQLTEST_VARDIR/tmp/ --parallel=2 mysql global_priv 2>&1
+
+set global debug_dbug=@save_debug_dbug;
+

mysql-test/main/mysqldump-win.opt

@@ -0,0 +1 @@
+--loose-enable-named-pipe

mysql-test/main/mysqldump-win.result

@@ -0,0 +1,9 @@
+# Test mysqldump specific features (pipe connection, with parallel)
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES(1);
+DROP TABLE t1;
+test.t1: Records: 1  Deleted: 0  Skipped: 0  Warnings: 0
+SELECT * FROM t1;
+i
+1
+DROP TABLE t1;

mysql-test/main/mysqldump-win.test

@@ -0,0 +1,14 @@
+--source include/windows.inc
+--source include/not_embedded.inc
+
+--echo # Test mysqldump specific features (pipe connection, with parallel)
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES(1);
+
+--exec $MYSQL_DUMP --host=. --tab=$MYSQLTEST_VARDIR/tmp/ test --parallel=2
+DROP TABLE t1;
+--exec $MYSQL test  < $MYSQLTEST_VARDIR/tmp/t1.sql
+--exec $MYSQL_IMPORT  test $MYSQLTEST_VARDIR/tmp/t1.txt
+SELECT * FROM t1;
+DROP TABLE t1;
+

mysql-test/main/mysqldump.result

@@ -6658,3 +6658,12 @@ drop table t1;
 # End of 10.4 tests
 #
 mariadb-dump: --xml can't be used with --tab.
+select @@max_connections into @save_max_connections;
+set global max_connections=10;
+mariadb-dump: Got error: 1040: "Too many connections" when trying to connect
+set global max_connections=300;
+mariadb-dump: Too many connections
+set global max_connections=@save_max_connections;
+#
+# End of 11.4 tests
+#

mysql-test/main/mysqldump.test

@@ -2482,7 +2482,7 @@ INSERT INTO t2 VALUES (3), (4);
 SELECT * FROM t1;
 SELECT * FROM t2;
 
---exec $MYSQL_DUMP --default-character-set=utf8mb4 --tab=$MYSQLTEST_VARDIR/tmp/ db_20772273
+--exec $MYSQL_DUMP --default-character-set=utf8mb4 --tab=$MYSQLTEST_VARDIR/tmp/ --parallel=2 db_20772273
 --exec $MYSQL db_20772273 < $MYSQLTEST_VARDIR/tmp/t1.sql
 --exec $MYSQL db_20772273 < $MYSQLTEST_VARDIR/tmp/t2.sql
 
@@ -3023,3 +3023,24 @@ drop table t1;
 --replace_result mariadb-dump.exe mariadb-dump
 --error 1
 --exec $MYSQL_DUMP --xml --tab=$MYSQLTEST_VARDIR/tmp 2>&1
+
+#
+# MDEV-32589 parallel-mysqldump - test "too many connections"
+#
+select @@max_connections into @save_max_connections;
+set global max_connections=10;
+--replace_result mariadb-dump.exe mariadb-dump
+--error 2
+--exec $MYSQL_DUMP --tab=$MYSQLTEST_VARDIR/tmp/ --parallel=20 mysql 2>&1
+#
+# MDEV-32589 test builtin 256 connections limit
+#
+set global max_connections=300;
+--replace_result mariadb-dump.exe mariadb-dump
+--error 1
+--exec $MYSQL_DUMP --tab=$MYSQLTEST_VARDIR/tmp/ --parallel=280 mysql 2>&1
+set global max_connections=@save_max_connections;
+
+--echo #
+--echo # End of 11.4 tests
+--echo #

sql/sql_class.cc

@@ -3399,6 +3399,9 @@ int select_export::send_data(List<Item> &items)
   uint used_length=0,items_left=items.elements;
   List_iterator_fast<Item> li(items);
 
+  DBUG_EXECUTE_IF("select_export_kill", {
+    thd->killed= KILL_QUERY;
+  });
   if (my_b_write(&cache,(uchar*) exchange->line_start->ptr(),
 		 exchange->line_start->length()))
     goto err;