在查询PostgreSQL数据库的黑盒函数上使用multiprocessing.Pool时出现"InterfaceError:连接已关闭“

import multiprocessing
import psycopg2

def query_database(query):
    conn = psycopg2.connect(database="your_database", user="your_user", password="your_password", host="your_host", port="your_port")
    cursor = conn.cursor()
    cursor.execute(query)
    result = cursor.fetchall()
    cursor.close()
    conn.close()
    return result

def process_task(task):
    query = task['query']
    result = query_database(query)
    # 处理查询结果
    # ...

if __name__ == '__main__':
    tasks = [{'query': 'SELECT * FROM table1'}, {'query': 'SELECT * FROM table2'}, ...]

    pool = multiprocessing.Pool()
    pool.map(process_task, tasks)
    pool.close()
    pool.join()