python - 无法在类中腌制 sqlAlchemy 引擎

Question

我想在我的自定义类中使用多处理模块和 sqlAlchemy。这是代码：

from sqlalchemy import create_engine
engine = create_engine(f'mysql+pymysql://a:b@localhost:3306/', server_side_cursors=True, pool_size=20)


class Client(object):
    def __init__(self):
        self.engine = create_engine(f'mysql+pymysql://a:b@localhost:3306/', server_side_cursors=True, pool_size=20)
        self.pool = Pool(6)

    def run_in_process(self, x): 
        conn = self.engine.connect()
        print(conn)

    def run(self):
        x = 'x' 
        res = self.pool.apply_async(self.run_in_process, (x,))
        res.get()

    def __getstate__(self):
        self_dict = self.__dict__.copy()
        del self_dict['pool']
        return self_dict

    def __setstate__(self, state):
        self.__dict__.update(state)


pool = Pool(6)
client = Client()
client.run()

它显示错误：

  File "test_pickle.py", line 32, in <module>
    client.run()
  File "test_pickle.py", line 19, in run
    res.get()
  File "/home/airflow/.pyenv/versions/3.7.3/lib/python3.7/multiprocessing/pool.py", line 657, in get
    raise self._value
  File "/home/airflow/.pyenv/versions/3.7.3/lib/python3.7/multiprocessing/pool.py", line 431, in _handle_tasks
    put(task)
  File "/home/airflow/.pyenv/versions/3.7.3/lib/python3.7/multiprocessing/connection.py", line 206, in send
    self._send_bytes(_ForkingPickler.dumps(obj))
  File "/home/airflow/.pyenv/versions/3.7.3/lib/python3.7/multiprocessing/reduction.py", line 51, in dumps
    cls(buf, protocol).dump(obj)
TypeError: can't pickle _thread._local objects

我知道多处理有时会因为pickle而很麻烦，而且我知道这个问题是由于self.engine，因为它不能被pickle。但我必须engine在课堂上使用这个变量。

那么，在我的示例中，如何使引擎可供选择？

提前致谢。

标签： pythonsqlalchemymultiprocessingpickle