停止读取Python中没有挂起的进程输出？
发布于 2021-02-02 23:15:42
我有一个用于Linux的Python程序，几乎像这样：
import os
import time
process = os.popen("top").readlines()
time.sleep(1)
os.popen("killall top")
print process
程序挂在此行：
process = os.popen("top").readlines()
而这种情况发生在保持更新输出的工具中，例如“ Top”
我最好的尝试：
import os
import time
import subprocess
process = subprocess.Popen('top')
time.sleep(2)
os.popen("killall top")
print process
它比第一个更好（它已经发了声），但是返回了：
<subprocess.Popen object at 0x97a50cc>
第二次审判：
import os
import time
import subprocess
process = subprocess.Popen('top').readlines()
time.sleep(2)
os.popen("killall top")
print process
与第一个相同。由于“ readlines（）”而挂起
它的返回应该是这样的：
top - 05:31:15 up 12:12, 5 users, load average: 0.25, 0.14, 0.11
Tasks: 174 total, 2 running, 172 sleeping, 0 stopped, 0 zombie
Cpu(s): 9.3%us, 3.8%sy, 0.1%ni, 85.9%id, 0.9%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 1992828k total, 1849456k used, 143372k free, 233048k buffers
Swap: 4602876k total, 0k used, 4602876k free, 1122780k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
31735 Barakat 20 0 246m 52m 20m S 19.4 2.7 13:54.91 totem
1907 root 20 0 91264 45m 15m S 1.9 2.3 38:54.14 Xorg
2138 Barakat 20 0 17356 5368 4284 S 1.9 0.3 3:00.15 at-spi-registry
2164 Barakat 9 -11 164m 7372 6252 S 1.9 0.4 2:54.58 pulseaudio
2394 Barakat 20 0 27212 9792 8256 S 1.9 0.5 6:01.48 multiload-apple
6498 Barakat 20 0 56364 30m 18m S 1.9 1.6 0:03.38 pyshell
1 root 20 0 2880 1416 1208 S 0.0 0.1 0:02.02 init
2 root 20 0 0 0 0 S 0.0 0.0 0:00.02 kthreadd
3 root RT 0 0 0 0 S 0.0 0.0 0:00.12 migration/0
4 root 20 0 0 0 0 S 0.0 0.0 0:02.07 ksoftirqd/0
5 root RT 0 0 0 0 S 0.0 0.0 0:00.00 watchdog/0
9 root 20 0 0 0 0 S 0.0 0.0 0:01.43 events/0
11 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuset
12 root 20 0 0 0 0 S 0.0 0.0 0:00.02 khelper
13 root 20 0 0 0 0 S 0.0 0.0 0:00.00 netns
14 root 20 0 0 0 0 S 0.0 0.0 0:00.00 async/mgr
15 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pm
并保存在变量“ process”中。我知道吗，我现在真的很困吗？
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1 个回答
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#!/usr/bin/env python """Start process; wait 2 seconds; kill the process; print all process output.""" import subprocess import tempfile import time def main(): # open temporary file (it automatically deleted when it is closed) # `Popen` requires `f.fileno()` so `SpooledTemporaryFile` adds nothing here f = tempfile.TemporaryFile() # start process, redirect stdout p = subprocess.Popen(["top"], stdout=f) # wait 2 seconds time.sleep(2) # kill process #NOTE: if it doesn't kill the process then `p.wait()` blocks forever p.terminate() p.wait() # wait for the process to terminate otherwise the output is garbled # print saved output f.seek(0) # rewind to the beginning of the file print f.read(), f.close() if __name__=="__main__": main()类似于尾巴的解决方案，仅打印输出的一部分
你可以在另一个线程中读取过程输出，并将所需数量的最后几行保存在队列中：import collections import subprocess import time import threading def read_output(process, append): for line in iter(process.stdout.readline, ""): append(line) def main(): # start process, redirect stdout process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True) try: # save last `number_of_lines` lines of the process output number_of_lines = 200 q = collections.deque(maxlen=number_of_lines) # atomic .append() t = threading.Thread(target=read_output, args=(process, q.append)) t.daemon = True t.start() # time.sleep(2) finally: process.terminate() #NOTE: it doesn't ensure the process termination # print saved lines print ''.join(q) if __name__=="__main__": main()此变体必须
q.append()是原子操作。否则，输出可能会损坏。signal.alarm()解
你可以用来 在指定的超时后signal.alarm()调用，process.terminate()而不用读入另一个线程。尽管它可能无法与subprocess模块很好地交互。基于@Alex Martelli的答案：import collections import signal import subprocess class Alarm(Exception): pass def alarm_handler(signum, frame): raise Alarm def main(): # start process, redirect stdout process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True) # set signal handler signal.signal(signal.SIGALRM, alarm_handler) signal.alarm(2) # produce SIGALRM in 2 seconds try: # save last `number_of_lines` lines of the process output number_of_lines = 200 q = collections.deque(maxlen=number_of_lines) for line in iter(process.stdout.readline, ""): q.append(line) signal.alarm(0) # cancel alarm except Alarm: process.terminate() finally: # print saved lines print ''.join(q) if __name__=="__main__": main()该方法仅适用于
* nix系统。如果process.stdout.readline()不返回，它可能会阻塞。threading.Timer 解 import collections import subprocess import threading def main(): # start process, redirect stdout process = subprocess.Popen(["top"], stdout=subprocess.PIPE, close_fds=True) # terminate process in timeout seconds timeout = 2 # seconds timer = threading.Timer(timeout, process.terminate) timer.start() # save last `number_of_lines` lines of the process output number_of_lines = 200 q = collections.deque(process.stdout, maxlen=number_of_lines) timer.cancel() # print saved lines print ''.join(q), if __name__=="__main__": main()这种方法在Windows上也应适用。在这里，我用作
process.stdout迭代。它可能会引入额外的输出缓冲，iter(process.stdout.readline, “”)如果不希望的话，你可以切换到该方法。如果进程没有终止，process.terminate()则脚本挂起。没有线程，没有信号解决方案
import collections import subprocess import sys import time def main(): args = sys.argv[1:] if not args: args = ['top'] # start process, redirect stdout process = subprocess.Popen(args, stdout=subprocess.PIPE, close_fds=True) # save last `number_of_lines` lines of the process output number_of_lines = 200 q = collections.deque(maxlen=number_of_lines) timeout = 2 # seconds now = start = time.time() while (now - start) < timeout: line = process.stdout.readline() if not line: break q.append(line) now = time.time() else: # on timeout process.terminate() # print saved lines print ''.join(q), if __name__=="__main__": main()此变型既不使用线程，也不使用信号，但会在终端中产生乱码输出。如果
process.stdout.readline()阻塞，它将阻塞。
