解决 pymongo 在linux 的子进程中操作父进程的链接报错，MongoClient opened before fork. Create MongoClient only after forking.

linux上不能在子进程中操作全局变量client的链接，否则报错。需要说明的是win的多进程不是fork实现的，所以子进程操作client没事

封装1个get_col的函数就行了。判断pid。

import os
from multiprocessing import Process

import pymongo.collection
from auto_run_on_remote import  run_current_script_on_remote
from pymongo import MongoClient

run_current_script_on_remote()

cleint = MongoClient(host='127.0.0.1')


pid__col_map = {}

def get_col(db:str,col:str,mongo_connect_url='mongodb://127.0.0.1') ->pymongo.collection.Collection:
    pid = os.getpid()
    key = (pid,mongo_connect_url,db,col)
    if key not in pid__col_map:
        pid__col_map[key] = MongoClient(mongo_connect_url).get_database(db).get_collection(col)
    return pid__col_map[key]


def col3() ->pymongo.collection.Collection:
    return get_col('testdb', 'col3')

def f():
    # cleint.get_database('testdb').get_collection('testcol').insert_one({"a":1})   # 如果在子进程中运行这个函数，这个在linux + pymongo 4.xx报错，在3.xx会警告。
    # get_col('testdb','testcol2').insert_one({"a":1})
    col3().insert_one({"b": 2})


if __name__ == '__main__':
    [Process(target=f).start() for i in range(3)]