AttributeError：由于多重处理，无法腌制本地对象“Flask.__init__.<locals>.<lambda>”

Question

我正在尝试在进程内运行网络服务器。 （跟进这个问题为什么我需要使用多处理：

在线程内停止破折号服务器不起作用）

这是一个小例子：

import logging
from dash import html, Dash
from flask import Flask
from multiprocessing import Process

############################## setup logger #############################
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s [%(threadName)s, %(levelname)s] %(message)s",
    handlers=[
        logging.FileHandler("logs.log"),
        logging.StreamHandler()
    ]
)
#########################################################################

class test:
    def __init__(self):
        flask_app = Flask(__name__)
        self.app = Dash(__name__, server=flask_app)

        # Define a simple layout
        self.app.layout = html.Div(children=[
            html.H1(children='Hello Dash'),
            html.P(children='This is a simple Dash app for testing.'),
            html.Button('Click Me', id='button')
        ])

    def prepare_webserver(self):      
        self.server_proc = Process(target=self.run_server, 
                                   name='dash_server', 
                                   daemon=True)
        self.server_proc.start()

    # Function to run the server
    def run_server(self):
        logging.info("Starting Dash server")
        self.app.run_server(debug=True, use_reloader=False)

if __name__ == "__main__":
    sim_manager = test()
    sim_manager.prepare_webserver()

我收到以下错误： 回溯（最近一次调用最后一次）：

  File "C:\Users\username\Desktop\Projects\python_framework\optimization_framework\test2.py", line 42, in <module>
    sim_manager.prepare_webserver()
  File "C:\Users\username\Desktop\Projects\python_framework\optimization_framework\test2.py", line 33, in prepare_webserver
    self.server_proc.start()
  File "C:\Users\username\AppData\Local\Programs\Python\Python310\lib\multiprocessing\process.py", line 121, in start
    self._popen = self._Popen(self)
  File "C:\Users\username\AppData\Local\Programs\Python\Python310\lib\multiprocessing\context.py", line 224, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "C:\Users\username\AppData\Local\Programs\Python\Python310\lib\multiprocessing\context.py", line 327, in _Popen
    return Popen(process_obj)
  File "C:\Users\username\AppData\Local\Programs\Python\Python310\lib\multiprocessing\popen_spawn_win32.py", line 93, in __init__
    reduction.dump(process_obj, to_child)
  File "C:\Users\username\AppData\Local\Programs\Python\Python310\lib\multiprocessing\reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)
AttributeError: Can't pickle local object 'Flask.__init__.<locals>.<lambda>'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Users\username\AppData\Local\Programs\Python\Python310\lib\multiprocessing\spawn.py", line 116, in spawn_main
    exitcode = _main(fd, parent_sentinel)
  File "C:\Users\username\AppData\Local\Programs\Python\Python310\lib\multiprocessing\spawn.py", line 126, in _main
    self = reduction.pickle.load(from_parent)
EOFError: Ran out of input

Answer 1

几乎可以肯定

self

 不可 pickle，因此您不能使用 

self.run_server

 作为目标。

尝试将

run_server()

 设置为静态方法。

    @staticmethod
    # Function to run the server
    def run_server():
        server = Test()
        logging.info("Starting Dash server")
        server.app.run_server(debug=True, use_reloader=False)

新进程没有理由需要传递经过腌制的现有服务器而不是创建自己的服务器。