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我正在尝试编写一个简单的脚本，该脚本将帮助我使用 mqtt 在多个 Raspberry Pi 上开始和停止视频播放。

这是我第一次尝试从 python 脚本启动和停止子进程，但我无法理解正确的操作顺序

有我的代码

import paho.mqtt.client as mqtt
import multiprocessing, time, signal
import os

def player(video):
    print("Playing " + video)
    os.system("omxplayer-sync " + video)

def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    client.subscribe("player/#")

def on_message(client, userdata, msg):    
    print(msg.topic+" "+str(msg.payload))
    if msg.topic == "player/PLAY":
        p = multiprocessing.Process(target=player, args=[str(msg.payload.decode())])
        p.start()
    if msg.topic == "player/STOP":
        print("Stopping video")
        print(p, p.is_alive())
        print("Terminating video")
        p.terminate()
        print(p, p.is_alive())

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect("localhost", 1883, 60)

client.loop_forever()

我可以成功启动视频，但我无法停止它。我很确定这是因为p对象在回调结束时被销毁，on_message但我看不到在哪里可以在其他地方创建我的进程。

编辑

这是使用 global 关键字的幼稚方法

import paho.mqtt.client as mqtt
import multiprocessing, time, signal
import os

videoFile = ""

class GracefulExit:
    kill_now = False
    def __init__(self):
        signal.signal(signal.SIGINT, self.exit_gracefully)
        signal.signal(signal.SIGTERM, self.exit_gracefully)

    def exit_gracefully(self,signum, frame):
        self.kill_now = True

def player():
    global videoFile
    print("Playing " + videoFile)
    os.system("omxplayer-sync " + videoFile)

def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    client.subscribe("player/#")

def on_message(client, userdata, msg):
    global videoFile
    print(msg.topic+" "+str(msg.payload))
    if msg.topic == "player/PLAY":
        videoFile = str(msg.payload.decode())
        p.start()
    if msg.topic == "player/STOP":
        print("Stopping video")
        print(p, p.is_alive())
        print("Terminating video")
        p.terminate()
        print(p, p.is_alive())

def main():
    app_killer = GracefulExit()
    while not app_killer.kill_now:
        try:
            time.sleep(0.5)
        except BaseException:
            print("Encountered an exeption.")
            break
    print ("End of the program.")

if __name__ == '__main__':
    print("Starting the program")
    client = mqtt.Client()
    client.on_connect = on_connect
    client.on_message = on_message
    client.connect("localhost", 1883, 60)
    client.loop_start()
    p = multiprocessing.Process(target=player)
    main()

但我只能播放一次视频并且通话terminate不会停止播放

编辑 2

现在我p按照建议声明为全局，但我不知道如何开始播放我从 MQTT 订阅接收的文件名

import paho.mqtt.client as mqtt
import multiprocessing, time, signal
import os

def player():
    print("Playing " + "synctest.mp4")
    os.system("omxplayer-sync " + "synctest.mp4")

p = multiprocessing.Process(target=player)

class GracefulExit:
    kill_now = False
    def __init__(self):
        signal.signal(signal.SIGINT, self.exit_gracefully)
        signal.signal(signal.SIGTERM, self.exit_gracefully)

    def exit_gracefully(self,signum, frame):
        self.kill_now = True

def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))
    client.subscribe("player/#")

def on_message(client, userdata, msg):
    print(msg.topic+" "+str(msg.payload))
    if msg.topic == "player/PLAY":
        print("p.args= " + p.name)
        videoFile = str(msg.payload.decode())
        #how to put the videoFile into the args given to p ?
        p.start()
    if msg.topic == "player/STOP":
        print("Stopping video")
        print(p, p.is_alive())
        print("Terminating video")
        p.terminate()
        print(p, p.is_alive())

def main():
    app_killer = GracefulExit()
    while not app_killer.kill_now:
        try:
            time.sleep(0.5)
        except BaseException:
            print("Encountered an exeption.")
            break
    print ("End of the program.")

if __name__ == '__main__':
    print("Starting the program")
    client = mqtt.Client()
    client.on_connect = on_connect
    client.on_message = on_message
    client.connect("localhost", 1883, 60)
    client.loop_start()
    main()
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