Python如何外部终止线程或在multiprocessing中使用input处理socket并发任务

问题根因 #

• 多进程模式下全局变量是独立拷贝的，父进程修改login状态不会同步到子进程，子进程的循环无法主动触发退出
• 调用terminate()强制终止子进程时，子进程正阻塞在input()调用上，标准输入流被强制关闭就会抛出EOFError
• 多进程会复制socket对象，父子进程同时持有套接字引用，会导致关闭逻辑异常

最优实现方案：单进程select多路复用 #

无需多进程/多线程，用select同时监听服务端socket和标准输入，两种事件互不阻塞，要终止时直接退出主循环即可，完全不存在强制终止任务的问题。
修改后的可运行代码如下：

import sys
import select
import socket
from socket import AF_INET, SOCK_STREAM

def main():
    server_port = int(sys.argv[1])
    serverName = 'localhost'
    clientSocket = socket(AF_INET, SOCK_STREAM)
    clientSocket.connect((serverName, server_port))
    login = False

    while True:
        # 同时监听socket和标准输入，超时设为0.1秒避免永久阻塞
        read_list, _, _ = select.select([clientSocket, sys.stdin], [], [], 0.1)
        
        for fd in read_list:
            # 服务端有消息下发
            if fd == clientSocket:
                received_message_encrypted = clientSocket.recv(1024)
                if not received_message_encrypted:
                    # 服务端断开连接
                    clientSocket.close()
                    return
                received_message = received_message_encrypted.decode('utf-8')
                if received_message == 'bye':
                    clientSocket.close()
                    return
                # 其他服务端消息处理逻辑写在这里
                print(received_message)
                # 登陆成功后才开启输入监听，可根据服务端登陆返回消息修改login状态
                if 'login success' in received_message:
                    login = True
            
            # 用户有输入
            elif fd == sys.stdin and login:
                command = input()
                if command == 'logout':
                    clientSocket.send(command.encode('utf-8'))
                    print('user has logged out')
                    clientSocket.close()
                    return
                elif command == 'whoelse':
                    clientSocket.send(command.encode('utf-8'))
                else:
                    clientSocket.send('giberish'.encode('utf-8'))

if __name__ == "__main__":
    main()

备选方案（坚持用线程的场景） #

如果一定要用多任务拆分输入和接收逻辑，使用daemon线程即可，主进程退出时会自动销毁daemon线程，不会抛出EOF错误：

import sys
import threading
import socket
from socket import AF_INET, SOCK_STREAM

login = True
clientSocket = None

def input_command():
    global login
    while login:
        command = input()
        if command == 'logout':
            clientSocket.send(command.encode('utf-8'))
            print('user has logged out')
            login = False
            break
        elif command == 'whoelse':
            clientSocket.send(command.encode('utf-8'))
        else:
            clientSocket.send('giberish'.encode('utf-8'))
    clientSocket.close()

def main():
    global clientSocket, login
    server_port = int(sys.argv[1])
    serverName = 'localhost'
    clientSocket = socket(AF_INET, SOCK_STREAM)
    clientSocket.connect((serverName, server_port))
    login = False
    once = False
    input_thread = None

    while True:
        received_message_encrypted = clientSocket.recv(1024)
        received_message = received_message_encrypted.decode('utf-8')
        if received_message == 'bye':
            login = False
            clientSocket.close()
            # 主进程直接退出，daemon线程会被自动回收
            sys.exit()

        if login and not once:
            once = True
            # 设置为daemon线程，主进程退出时自动销毁
            input_thread = threading.Thread(target=input_command, daemon=True)
            input_thread.start()

if __name__ == "__main__":
    main()

内容的提问来源于stack exchange，提问作者Dizzy