为什么这个python脚本只能在Ubuntu 12.04上使用IDLE？

Question

Edit Written in C it works like a champ. I began noticing that the python would fail unpredictably. The bash solution worked too but I wanted to be able to easily check if it was running so I wrote the C version so I can see it when I do a ps -e .

In an attempt to address this issue and the real problem (VLC player continues to inhibit power management daemon after playback has ended) I wrote the following script. It works when I run it from IDLE but not from terminal. My ultimate goal is to have this script run as a startup application. I'm using Ubuntu 12.04 and Python 2.7.3. What do I need to change to achieve the desired result? Please forgive my amateur python skills. Thanks in advance

EDIT: The script runs in terminal since I took out t.daemon = True (thanks Max Noel) however the script still doesn't run as a startup application using the command python /path/to/script/vlc_watchdog.py and also I noticed that when it is run from terminal, it only works so long as the terminal window remains open. I want this process to go run off and be happy and free and independent of it's parent, even after the parent is closed/killed. How do I make that happen?

What almost worked: sudo apt-get install python-daemon ; add import daemon to the script ; move import time to the top and add time.sleep(30) immediately after ; do away with all the thread stuff and in it's place put with daemon.DaemonContext(): run() ; in the Startup Applications window of Ubuntu 12.04 add an entry that executes the command python /path/to/script/vlc_watchdog_daemon.py & . That & at the end is important. My best guess (and I'm a n00b at both Ubuntu and Python) is that there was something(s) that wasn't fully loaded and this not-quite-fully-loaded condition was causing the script to behave abnormally. That is why I added the sleep immediately following the import time and added the & at the end of the Startup Applications command. I could have perhaps gotten away with doing less but after the headache I'm at the point where "IT WORKS DON'T TOUCH IT!!!" It may be possible to remove "fixes" and still get it to work. You the reader are welcome to try. I'm good. Final version of script at end of question.

Original Version Didn't Quite Work as a Startup Script but works from IDLE and Terminal:

#vlc_watchdog.py  version 0.1
import dbus
import os
import time
import subprocess
from subprocess import Popen, PIPE
from threading import Thread

def vlc_killer():
    bus = dbus.SessionBus()
    vlc_media_player_obj = bus.get_object("org.mpris.MediaPlayer2.vlc", "/org/mpris/MediaPlayer2")
    props_iface = dbus.Interface(vlc_media_player_obj, 'org.freedesktop.DBus.Properties')
    pb_stat = props_iface.Get('org.mpris.MediaPlayer2.Player', 'PlaybackStatus')
    if pb_stat == 'Stopped':
        os.system("kill -9 $(pidof vlc)")

def vlc_is_running():
    ps = subprocess.Popen(['ps', '-e'], stdout = PIPE)
    out, err = ps.communicate()
    for line in out.splitlines():
        if 'vlc' in line:
            return True
    return False

def run():
    while True:
        if vlc_is_running():
            vlc_killer()
        else:
            time.sleep(30)

t = Thread(target=run)
#t.daemon = True  <-- this is what broke it.  Thanks Max Noel
t.start()

Final Version Works as Intended:

#!/usr/bin/env python
import time
time.sleep(30)
import dbus
import os
import subprocess
from subprocess import Popen, PIPE
import daemon
import setproctitle

sleeptime = 15

def vlc_killer():
    bus = dbus.SessionBus()
    vlc_media_player_obj = bus.get_object("org.mpris.MediaPlayer2.vlc", "/org/mpris/MediaPlayer2")
    props_iface = dbus.Interface(vlc_media_player_obj, 'org.freedesktop.DBus.Properties')
    pb_stat = props_iface.Get('org.mpris.MediaPlayer2.Player', 'PlaybackStatus')
    if pb_stat == 'Stopped':
        os.system("kill -9 $(pidof vlc)")
    else:
        time.sleep(sleeptime)

def vlc_is_running():
    ps = subprocess.Popen(['ps', '-e'], stdout = PIPE)
    out, err = ps.communicate()
    for line in out.splitlines():
        if 'vlc' in line:
            return True
    return False

def run():
    setproctitle.setproctitle('vlc-watchdog')
    while True:
        if vlc_is_running():
            vlc_killer()
        else:
            time.sleep(sleeptime)

with daemon.DaemonContext():
    run()

Executed at startup by adding python /path/to/script/vlc_watchdog_daemon.py & to the Startup Applications window in Ubuntu 12.04. See Adding Startup Applications for detailed instructions. I'm running Python 2.7.3.

Answer 1

Your thread has daemon = True . Your Python program will terminate as soon as the only threads left running are daemonic threads (see http://docs.python.org/2/library/threading.html#thread-objects ).

So what's happening is that at the precise moment your t.start() call happens, your main thread reaches its end. The Python VM checks what threads are left running, finds only t , which is daemonic, and terminates without executing any of the code in your run method.

The reason why this works in IDLE is that IDLE runs your Python code inside its own Python process, instead of spawning a new one. So when you reach the end of your code, the Python VM checks what threads are left running, finds a lot of them (non-daemonic) because there's an entire IDE still inside and doesn't terminate, so your code keeps running and kills VLC.

Furthermore, I see no need for your code to run in a separate thread (your main thread, after all, does nothing). Just do away with that entirely, and have your watchdog program simply be that while loop.