python 多线程问题

原代码:

while True:
    conn, cur_pgsql = self.connectPGSQL()
    sql = "SELECT id,file_path FROM listed_companies.company_new_notice WHERE file_path_ is null and id > {0}  limit 20".format(index)
    cur_pgsql.execute(sql)
    items = cur_pgsql.fetchall()
    cur_pgsql.close()
    conn.close()
    with ThreadPoolExecutor(max_workers=20) as pool:
        pool.map(self.downloadPDF, items)
    index += 20

运行后没反应，Ctrl+c后就有了如下报错信息

Traceback (most recent call last):
  File "company_new_notice.py", line 224, in <module>
    spider.downloadUrl()
  File "company_new_notice.py", line 218, in downloadUrl
    pool.map(self.downloadPDF, items)
  File "/data01/python3/lib/python3.6/concurrent/futures/_base.py", line 581, in __exit__
    self.shutdown(wait=True)
  File "/data01/python3/lib/python3.6/concurrent/futures/thread.py", line 144, in shutdown
    t.join()
  File "/data01/python3/lib/python3.6/threading.py", line 1056, in join
    self._wait_for_tstate_lock()
  File "/data01/python3/lib/python3.6/threading.py", line 1072, in _wait_for_tstate_lock
    elif lock.acquire(block, timeout):
KeyboardInterrupt
^CError in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/data01/python3/lib/python3.6/concurrent/futures/thread.py", line 39, in _python_exit
    t.join()
  File "/data01/python3/lib/python3.6/threading.py", line 1056, in join
    self._wait_for_tstate_lock()
  File "/data01/python3/lib/python3.6/threading.py", line 1072, in _wait_for_tstate_lock
    elif lock.acquire(block, timeout):
KeyboardInterrupt