master server starts slave parallel threads

ERROR 1198 (HY000): This operation cannot be performed as you have a running slave ''; run STOP SLAVE '' first

master [localhost] {msandbox} ((none)) > select ID, DB, state, time_ms, memory_used from information_schema .PROCESSLIST where USER='system user';

Empty set (0.01 sec)

master [localhost] {msandbox} ((none)) > set global slave_parallel_threads=10;

Query OK, 0 rows affected (0.00 sec)

master [localhost] {msandbox} ((none)) > select ID, DB, state, time_ms, memory_used from information_schema .PROCESSLIST where USER='system user';

+----+------+----------------------------------+----------+-------------+

| ID | DB   | state                            | time_ms  | memory_used |

+----+------+----------------------------------+----------+-------------+

| 47 | NULL | Waiting for work from SQL thread | 2207.683 |       34704 |

| 46 | NULL | Waiting for work from SQL thread | 2207.686 |       34704 |

| 45 | NULL | Waiting for work from SQL thread | 2207.722 |       34704 |

| 44 | NULL | Waiting for work from SQL thread | 2207.723 |       34704 |

| 43 | NULL | Waiting for work from SQL thread | 2207.754 |       34704 |

| 42 | NULL | Waiting for work from SQL thread | 2207.757 |       34704 |

| 41 | NULL | Waiting for work from SQL thread | 2207.765 |       34704 |

| 40 | NULL | Waiting for work from SQL thread | 2207.801 |       34704 |

| 39 | NULL | Waiting for work from SQL thread | 2207.843 |       34704 |

| 38 | NULL | Waiting for work from SQL thread | 2207.851 |       34704 |

+----+------+----------------------------------+----------+-------------+

10 rows in set (0.01 sec)